International and National Journals

P. Allia, F. Celegato, M. Coïsson, P. Tiberto, F. Vinai
Different aggregation states in Cu/Co multilayers prepared by RF sputtering on rotating substrates
Journal of Magnetism and Magnetic Materials, Vol. 316, no. 2, pp. E5-E8, 2007 (IF 1,704).

Co/Cu multilayers with different Co/Cu ratio were prepared by RF sputtering on Si₃N₄ substrates in Ar atmosphere by the rotating-substrate technique. The samples were produced with five subsequent expositions of the substrate, rotating at nine angular velocities between 0.23 and 0.63 rad/s. Room temperature measurements of magnetization and magnetoresistance point to a gradual transition from a multilayered to a granular structure on increasing the angular velocity of the substrate.

P. Allia, M. Coïsson, P. Tiberto, F. Vinai
Magnetic and magnetotransport properties in Joule-heated granular Cu₉₅Co₅ ribbons
Journal of Alloys and Compounds, Vol. 434, pp. 601-603, 2007 (IF 1,455).

Cu₉₅Co₅ alloys, consisting of Co nanoparticles, were obtained by subjecting rapidly quenched ribbons to suitable dc Joule-heating treatments (0 ≤ I ≤ 5.75 A for 60 s) in order to induce different degrees of Co precipitation with particles having different average size. The behaviour of the resistance versus applied field is influenced by the structural changes (Co cluster formation) that occur in the samples after different thermal treatments. The dependance of the electric and magnetic properties on microstructural configurations has been studied by measuring room-temperature hysteresis loops and GMR. By combining the GMR response with magnetization data, information on the magnetic correlation between magnetic moments of neighbouring Co particles will be obtained and correlated to the different microstructures induced by current annealing.

E. Barbisio, O. Bottauscio, M. Chiampi, G. Crotti, D. Giordano
Experimental and modelling analysis of ferroresonant electric circuits
Journal of Magnetism and Magnetic Materials, Vol. 316, pp. e299-e301, 2007 (IF 1,704).

This paper presents a numerical and an experimental investigation on the ferroresonance in a LCR series electric circuit with the aim of deepening the effects of the magnetization phenomena in the ferromagnetic core. In the experiments an Epstein-like FeSi core, enabling an accurate material characterization under the same test conditions, constitutes the non-linear inductance. The model couples the circuit equations with a finite element solution of the one-dimensional electromagnetic field along the lamination thickness. The analysis of the numerical results, which are confirmed by experiments, shows that the accurate prediction of ferroresonance requires the use of detailed constitutive models, when the role of the magnetic losses is significant.

V. Basso, C.P. Sasso, M. Lo Bue
Thermodynamic aspects of first order phase transformations with hysteresis in magnetic materials
Journal of Magnetism and Magnetic Materials, Vol. 316, pp. 262-268, 2007 (IF 1,704).

In this paper we study first-order phase transformations between two stable phases with different crystal structures and magnetic order. The out-of-equilibrium thermodynamics of the hysteretic phase transformation is formulated for a collection of bistable objects by considering the two stable states as two generic phases, say 0 and 1. In the phase coexistence region we compute the magnetization, the entropy and the entropy production. Results are obtained by deriving the model parameters from experimental data on Gd-Si-Ge and giving prediction on temperature driven hysteresis, and on the heat flux with the thermal bath.

C. Beatrice, O. Bottauscio, F. Fiorillo, E. Patroi
Hysteresis loop measurements in rare-earth based permanent magnets: the role of applied field rate and sample geometry
Journal of Optoelectronics and Advanced Materials, Vol. 9, no. 4, pp. 1120-1126, 2007 (IF 0,827).

Methods currently employed in the characterization of hard magnets are briefly discussed and the challenges posed by the precise measurement of the hysteresis loop and its parameters in rare-earth based permanent magnets are stressed. It is shown that fast and reliable measurements can be performed using the Pulsed Field Magnetometer method, exploiting either the magnetometric or the fluxmetric approach. Full assessment of the obtained results calls for appraisal of the dynamic phenomena engendered by the fast changing applied field. Besides the ubiquitous magnetic aftereffect, eddy currents may lead to loop swelling in sintered rare-earth based samples. It is demonstrated that the role of eddy currents can be accounted for and the quasi-static hysteresis loop can be retrieved by simple analytical formulation.

S. M. Becchi, L. Callegaro, F. Durbiano, V. D'Elia, A. Strigazzi
Novel impedance cell for low conductive liquids: determination of bulk- and interface contributions
Review of Scientific Instruments, no. 78, p. 113902, 2007 (IF 1,384).

A plane capacitor cell with variable gap has been designed in order to detect the complex permittivity of low conductive liquids (up to 500 µS/cm) and the impedance of the sample-electrode interface. The novelty of the cell consists of the simultaneous presence of the field uniformity ensured by a guard ring, an adjustable gap between 300 µm and 6.75 mm (the electrode axial motion avoiding any rotation), and the immersion of the capacitor in the sample reservoir. The size of the capacitor electrodes and the gap values have been tested via the capacitance detection of the in-air cell at 1 kHz. The sample measurements have been performed by scanning the frequency range between 15 Hz and 2 MHz at four different capacitor gap values. In the paper a method to directly extract the bulk complex permittivity and the interface impedance versus frequency is presented. It is based on the assumption that the interface contribution is independent of the electrode gap, as confirmed (within the measurement accuracy) from measurements on all samples investigated. As samples of interest, we have chosen two certified electrolytic conductivity standards, KCl aqueous solutions having conductivity traceable to SI units; and two polymer latex aqueous dispersions of microspheres. Regarding KCl solutions, the conductivity measurements are compatible with the reference values within the specified uncertainty; the measured permittivities are consistent with the literature. For all samples, we have recovered the expected result that the interface impedance mainly affects the low frequency range (f<10 kHz).

G. Bertotti, P. Bortolotti, A. Magni, V. Basso
Topological and energetic aspects of the random-field Ising model
Journal of Applied Physics, Vol. 101, no. 9, Art. No. 09D508, 2007 (IF 2,171).

We show that random-field Ising model spin states are organized in equivalence classes (basins), each class containing the states that can be mutually reached from one another by some field history. Of these basins, only one contains the field-reachable states which can be generated by applying a suitable field history to one of the saturation states. We show that the basins form an oriented graph of which the basin of field-reachable states represents the bottom. The graph exhibits a hierarchical structure which reflects the organization in real space of the spin blocks that can be reversed back and forth by the field in some appropriate field interval without affecting the state of surrounding spins.

G. Bertotti, C. Serpico, I.D. Mayergoyz, R. Bonin, M. d'Aquino
Current-induced magnetization dynamics in nanomagnets
Journal of Magnetism and Magnetic Materials, Vol. 316, no.2, pp.285-290, 2007 (IF 1,704).

An overview is given of the various approaches that have been proposed for the interpretation of spin-transfer-driven magnetization dynamics. Models of critical currents and critical fields for switching as well as for the onset of magnetization oscillations are discussed, together with methods for the construction of field-current stability diagrams. Finally, the role of thermal fluctuations is analyzed. Particular emphasis is given to the study of uniformly magnetized nanomagnets, which represents an essential step before moving to the numerical computation of more complex micromagnetic configurations.

R. Bonin, G. Bertotti, C. Serpico, I.D. Mayergoyz, M. d'Aquino
Model of phase locking in spin-transfer-driven magnetization dynamics
Journal of Applied Physics, Vol. 101, pp. 09A506, 2007 (IF 2,171).

A simplified model of phase locking is discussed, which can be fully solved in analytical terms with no limitations as to the intensity of the coupling mechanism responsible for the locking. A nanomagnet with uniaxial symmetry is considered, jointly driven by a spin-polarized current, a dc magnetic field along the symmetry axis, and a radio-frequency circularly polarized magnetic field. The conditions are determined under which locking occurs between current-induced oscillations and the action of the rf field. The locking effect exhibits hysteresis as a function of the current.

R. Bonin, C. Serpico, G. Bertotti, I.D. Mayergoyz, M. d'Aquino
Analytical study of magnetization dynamics driven by spin-polarized currents
European Physical Journal B, Vol. 59, no. 4, pp. 435-445, 2007 (IF 1,356).

An analytical approach is presented for the study of magnetization dynamics driven by spin- polarized currents. Two cases are considered: (i) magnetic layers with in-plane uniaxial anisotropy; (ii) magnetic layers with uniaxial anisotropy and applied field perpendicular to the layer plane. Theoretical predictions are obtained for the existence of stationary modes and self-oscillations of magnetization by solving the deterministic Landau-Lifshitz-Gilbert equation with Slonczewski spin-torque term. Thermal fluctuations are studied by deriving the corresponding Fokker-Planck equation for the magnetization probability distribution. Analytical procedures to estimate the effective potential barrier separating self-oscillatory regimes and/or stationary modes are proposed.

S. Borini, L. Boarino, G. Amato
Anisotropic electrical response of mesoporous silicon to NO₂
Physica Status Solidi A, Vol. 204, no. 5, pp. 1408-1411, 2007 (IF 1,214).

The I-V characteristics of Mesoporous Silicon (mesoPS) samples have been studied both in vacuum and in presence of NO₂ traces. By the use of different electrode configurations, the longitudinal (parallel to the sample surface) and transverse (perpendicular to the sample surface) components of the electrical conductance have been independently measured and compared. We show that the electrical response of mesoPS to NO₂ is anisotropic, and that the best sensing performance is achieved by monitoring the longitudinal conductance variation.

S. Borini, L. Boarino, G. Amato
Coulomb blockade sensors based on nanostructured mesoporous silicon
Physica E - Low-Dimensional Systems & Nanostructures, Vol. 38, nos. 1-2, pp. 197-199, 2007 (IF 0,834).

Mesoporous silicon (mesoPS) is a nanosponge where Si nanocrystals are interconnected forming a disordered 3D array. The electronic characteristics of this material are particularly interesting, due to some intriguing effects, such as a huge increase of conductivity, reversible insulator-to-metal transition and n- or p-type doping of the nanocrystals, exhibited in presence of donor or acceptor molecules like NH₃ and NO₂. Here we report on the observation of a sharp conductance gap, which can be ascribed to Coulomb blockade phenomena. Moreover, we show that the width of the gap can be tuned by NO₂ molecules, so that the fabrication of highly sensitive threshold sensors is possible. Our results suggest that electrochemical etching of heavily doped Si can be used as a simple self-assembly technique for the production of Si nanocrystal arrays and for the fabrication of sensitive nanosensors.

S. Borini, L. Boarino, G. Amato
Slow conductivity relaxation and simple aging in nanostructured mesoporous silicon at room temperature
Physical Review B, Vol. 75, no. 16, p. 165205, 2007 (IF 3,172).

Experimental observations of peculiar time-dependent charge transport phenomena, such as slow conductivity relaxation, nonergodicity, and simple aging, are reported here for mesoporous silicon at room temperature. These effects are discussed on the basis of the strong disorder in the nanocrystalline silicon network constituting the material. Taking into account various independent results reported in literature, the authors suggest that the observed behavior may reflect nonequilibrium glassy dynamics due to Anderson localization and Coulomb interactions.

S. Borini
Effect of ammonia adsorption on the electrical characteristics of mesoporous silicon
Journal of Applied Physics, Vol. 102, p. 93709, 2007 (IF 2,171).

A detailed study of the current-voltage curves of mesoporous silicon mesoPS has been carried out for various dosages of ammonia, employing two different measurement configurations. The gas adsorption strongly modifies the electrical characteristics of the material, both affecting their shape and varying the conductivity values. In particular, it is found that the conductivity gap, arising from a collective Coulomb blockade phenomenon, and the electrical anisotropy of mesoPS can be gradually cancelled by NH₃ molecules. Moreover, a nonmonotonic behavior of the conductivity with respect to the gas pressure is observed, in analogy with previous infrared spectroscopy results. From the analysis of such experimental findings, we propose an interaction mechanism between the mesoPS surface and ammonia, involving the screening of trapped positive charges through the dipole moment of NH₃ molecules.

M. Borsero, G. Vizio, D. Parena, V. Teppati
Synthetic TDR measurements for TEM and GTEM cell characterization
IEEE Transactions on Instrumentation and Measurement, Vol. 56, no. 2, pp. 271-274, 2007 (IF 0,832).

This paper describes the main features of the Time Domain Reflectometry (TDR) measurement technique, and in particular the TDR analysis performed using a proper operating mode of the Vector Network Analyzer (VNA), called Synthetic TDR. Furthermore, some results of the reflection measurements, aimed to characterize the impedance behavior of the INRIM TEM and GTEM cells by means of a commercial VNA in time domain mode are presented.

P. Bortolotti, V. Basso, A. Magni, G. Bertotti
Dynamical-system-theory approach to the study of metastable states in the random field Ising model
Journal of Magnetism and Magnetic Materials, Vol. 310, pp. 1543-1545, 2007 (IF 1,704).

In this paper, we obtain information about the topological structure of the energy landscape of the random-field Ising model by numerical simulations. We define and construct a suitable map (one-loop map) for the representation of generic metastable state. We show that the properties of this map are strictly related to the possibility of generating the state by a field history.

O. Bottauscio, M. Chiampi, A. Manzin, P.E. Roccato, M. Zucca
A multiscale approach to the analysis of magnetic grid shields and its validation
Journal of Computational Physics, Vol. 227, pp. 1470-1482, 2007 (IF 2,372).

This paper illustrates the application of the multiple scale expansion theory to the analysis of heterogeneous thin structures employed for the magnetic field shielding and, in particular, the attention is focused on grid shields. These structures are conveniently employed in the mitigation of magnetic fields when the thermal dissipation is a severe restriction. The problem modelling is faced by applying the thin-shell approximation to the Maxwell equations, introducing appropriate interface conditions between the shield surfaces. Starting from this formulation, a homogenisation technique, based on the multiple scale expansion theory, is developed in order to replace the heterogeneous structure with an equivalent homogenous one. The proposed method enables an efficient analysis of magnetic and pure conductive heterogeneous shields with a significant decrease of the computational burden. The results are validated by comparison with a standard modelling approach, when possible, and with experiments developed on specific laboratory set-ups for frequencies up to 2kHz.

O. Bottauscio, V.C. Piat, M. Chiampi, M. Codegone, A. Manzin
Evaluation of effective electromagnetic properties in heterogeneous media
European Physical Journal - Applied Physics, Vol. 39, no. 2, pp. 113-118, 2007 (IF 0,778).

This paper presents the application of a homogenisation technique, based on the multi-scale expansion theory, to the analysis of heterogeneous materials constituted of magnetic inclusions dispersed in a dielectric lattice. The role of the shape and dimensions of the inclusions is analysed with reference to the effective electromagnetic properties and energy losses. The investigation is extended to the influence of flux waveforms with harmonic distortion, focusing the attention on the energy loss dependency on the harmonic content.

L. Brunetti, L. Oberto, E. T. Vremera
Thermoelectric Sensors as Microcalorimeter Load
IEEE Transactions on Instrumentation and Measurement, Vol. 56, no. 6, 2007 (IF 0,832).

Thermoelectric power sensors, instead of bolometers, can now be used as transfer standards in the microcalorimeter technique. This alternative has the technical advantages of being less sensitive to absolute temperature and not downward frequency limited. At the Istituto Nazionale di Ricerca Metrologica, the high-frequency power standards are based on coaxial thermocouples that operate in the frequency range that spans from direct current to 34 GHz. Modified commercial thermocouple mounts in the 7- and 3.5-mm coaxial lines are used to realize the national power standard with an accuracy ranging from 0.03% to 1% in the aforementioned frequency range.

L. Callegaro, V. D'Elia, P.P. Capra, A. Sosso
Techniques for traceable measurements of small currents
IEEE Transactions on Instrumentation and Measurement, Vol. 56, no. 2, pp. 295-299, 2007 (IF 0,832).

The Italian national standard of direct current is being extended down to the femtoampere range. Two current sources have been developed. The first one, working in the 100 pA to 100 fA range, is based on a low-frequency trapezoidal wave generator, measured with a sampling digital voltmeter at regular time intervals, which charges and discharges a gas-dielectric capacitor. The second, working in the 10 microA to 10 pA range, makes use of a calibrated resistor to generate a known current. Current is traceable to national standards of voltage, resistance or capacitance, and frequency.

L. Callegaro, V. D'Elia, B. Trinchera
A Current Source for Picoammeter Calibration
IEEE Transactions on Instrumentation and Measurement, Vol. 56, no. 4, pp. 1198-1201, 2007 (IF 0,832).

A current source, which is to be employed in the calibration of low-current meters (picoammeters and electrometers), is presented here. The output current range is 100 fA to 100 pA and is directly traceable to calibrated standards of dc voltage, capacitance, and time period. The source is based on a low- frequency (ap1 mHz) trapezoidal signal generator, which charges and discharges a gas-dielectric capacitor; the voltage is monitored with a voltmeter that is triggered by a precision time base. The source has been employed during March 2006 for the Italian participation to the supplementary comparison EUROMET.EM-S24 and will be part of an extension of the Italian national standard of dc current. However, being composed of low-cost electronics and common commercial instrumentation, the source can also find useful application in secondary calibration laboratories.

L. Callegaro
EUROMET.EM-S20: Intercomparison of a 100 mH inductance standard (Euromet Project 607)
Metrologia, Vol. 44, art. 01002 (online) (IF 1,667).

The report describes the organization, equipment and results of the EUROMET.EM-S20 supplementary comparison "Intercomparison of a 100 mH inductance standard", in the context of the EUROMET Project no. 607. The comparison took place from November 2002 to June 2003, and involved seven participants. The travelling standard was purposely built from a General Radio 1482-L inductor, thermostatted and configured to be measured as a two-terminal or as a four-terminal-pair impedance. Participants from national metrology institutes measured it as a two-terminal standard at the frequency of 1 kHz, and a reference value was determined for this configuration with a relative uncertainty of 4.2 µH/H. All estimates reported by the participants are in agreement with the reference value, within the corresponding expanded uncertainties (95% level of confidence). The travelling standard and a part of the comparison protocol are at present being employed in the organization of the EUROMET.EM-S26 follow-up comparison, in the context of the EUROMET Project no. 816.

F. Celegato, M. Coisson, S.N. Kane, P. Tiberto, F. Vinai
High-frequency magnetoimpedance on annealed amorphous magnetic wires with different magneto striction constants
Journal of Non-Crystalline Solids, Vol. 353, nos. 8-10, pp. 919-921, 2007 (IF 1,319).

Amorphous Co-based and Fe-based magnetic wires having magnetostriction constants ranging from nearly zero positive values to large positive values, have been submitted to different thermal treatments (dc Joule heating and furnace annealing) to relax internal stresses produced during fabrication and to possibly induce different magnetic anisotropy. High-frequency (up to 6 GHz) magnetoimpedance GMI response has been studied as a function of frequency and thermal treatment in order to experimentally investigate the role of all these parameters on GMI.

F. Celegato, M. Coisson, A. Magni, P. Tiberto, F. Vinai, S.N. Kane, A. Gupta, P. Sharma
Study of magnetic properties and relaxation in amorphous Fe_73.9Nb_3.1Cu_0.9Si_13.2B_8.9thin films produced by ion beam sputtering
Journal of Applied Physics, Vol. 102, pp. 043916-1- 043916-8, 2007 (IF 2,171).

Amorphous Fe_73.9Nb_3.1Cu_0.9Si_13.2B_8.9 thin films have been produced by ion beam sputtering with two different beam energies (500 and 1000 eV). Magnetic measurements indicate that the samples display a uniaxial magnetic anisotropy, especially for samples prepared with the lower beam energy. Magnetization relaxation has been measured on both films with an alternating gradient force magnetometer and magneto-optical Kerr effect. Magnetization relaxation occurs on time scales of tens of seconds and can be described with a single stretched exponential function. Relaxation intensity turns out to be higher when measured along the easy magnetization axis.

M. Chiampi, G. Crotti, D. Giordano
Set up and characterization of a system for the generation of reference magnetic fields from 1 to 100 kHz
IEEE Transactions on Instrumentation and Measurement, Vol. 56, no. 2, pp. 300-304, 2007 (IF 0,832).

This paper describes the design process, the specific features, and the characterization procedures of the Istituto Nazionale di Ricerca Metrologica (I.N.RI.M.) set up for the generation of reference magnetic fields in the frequency range from 1 to 100 kHz. Numerical techniques, validated by comparison with experimental data, make it possible to choose the best solutions for obtaining magnetic flux densities up to 100 µT at 1 kHz and 25 µT at 100 kHz with relative uncertainty from a few parts in 103 up to the percent.

A. Chiolerio, P. Allia, A. Chiodoni, F. Pirri, F. Celegato, M. Coisson
Thermally evaporated Cu--Co top spin valve with random exchange bias
Journal of Applied Physics, Vol. 101, art. 123915, 2007 (IF 2,171).

A cobalt-copper top spin valve was prepared by thermal evaporation of a stack of ferromagnetic thin ?lms separated by thin layers of the diamagnetic metal, with a cap layer containing an antiferromagnetic (AFM) exchange-biasing material. A nonconventional top AFM layer was used, in order to optimize the multilayer roughness and to avoid electrical interference with metallic layers; it consists of a composite material easily processed by means of optical lithography, basically a polymeric matrix composite with a dispersion of nickel oxide microparticles. Magnetization and magnetoresistance measurements were performed from 4 to 300 K. The measurements of both quantities indicate random pinning action of the top AFM layer, resulting in a small exchange-bias ?eld and in asymmetric magnetization and magnetoresistance curves. A simple model explains the observed physical effects.

F. Colaiori, G. Durin, S. Zapperi
Eddy current damping of a moving domain wall: beyond the quasistatic approximation
Physical Review B, 76 (2007), pp. 224416 (IF 3,172).

In conducting ferromagnetic materials, a moving domain wall induces eddy currents in the sample, which give rise to an effective retarding pressure on the domain wall. We show here that the pressure is not just proportional to the instantaneous velocity of the wall, as often assumed in domain wall models, but depends on the history of the motion. We calculate the retarding pressure by solving the Maxwell equations for the field generated by the eddy currents and show how its effect can be accounted for by associating a negative effective mass to the magnetic wall. We analyze the dependence of this effect on the sample geometry and discuss the implications for the Barkhausen noise measurements.

F. Colaiori, G. Durin, S. Zapperi
Loss separation for dynamics hysteresis in magnetic thin films
Journal of Magnetism and Magnetic Materials, Vol. 316, pp. e549-e551, 2007 (IF 1,704).

We show that the properties of dynamic hysteresis in ferromagnetic thin films can be explained in terms of the theory of loss separation. Remarkably, this theory, that was originally derived for bulk metallic materials, is applicable to disordered magnetic systems under fairly general conditions regardless of the particular damping mechanism. This is confirmed by numerical simulations of a driven random-field Ising model. We re-examine several experimental data reported in the literature on dynamic hysteresis in thin films and find that all of them find a natural interpretation in terms of loss separation, reconciling the apparent lack of universality observed in different materials.

M. d'Aquino, G. Bertotti, G. Guida, C. Serpico, I.D. Mayergoyz
Foldover, quasi-periodicity, parametric instabilities in ultra-thin films subject to rf fields
Journal of Magnetism and Magnetic Materials, Vol. 316, pp. e523-e525, 2007 (IF 1,704).

We study magnetization dynamics in a uniaxial ultra-thin ferromagnetic disk subject to spatially uniform microwave external fields.The rotational invariance of the system is such that the only admissible spatially uniform steady states are periodic (P-modes) and quasi-periodic (Q-modes) modes. The stability of P-modes versus spatially uniform and nonuniform perturbations is studied by using spin-wave analysis and the instability diagram for all possible P-modes is computed. The predictions of the spin-wave analysis are compared with micromagnetic simulations.

L. De Stefano, I. Rendina, A.M. Rossi, M.E. Rossi, L. Rotiroti, S. D'Auria
Biochips at work: porous silicon microbiosensor for proteomic diagnostic
Journal of Physics-Condensed Matter, Vol. 19, no. 39, Art. no. 395007, 2007 (IF 1,886).

The molecular interactions between the glutamine binding-protein (GlnBP) from Escherichia coli and its main ligands the L-glutamine (Gln) and the gliadin, a toxic peptide containing three Gln sequences, are detected by means of an optical biosensor based on porous silicon (PSi) technology. The binding events are optically transduced in the wavelength shifts of the porous silicon reflectivity spectrum. In the first case, the hydrophobic interaction links the GlnBP, which acts as a molecular probe for Gln, to the hydrogenated porous silicon surface area. A more stable coupling between the protein and the chip surface can be obtained by a proper functionalization process. Even if the GlnBPs are covalently bonded to the PSi, they are able to selectively recognize the gliadin in micromolar concentration.

F. Durbiano, A. Manzin, P. P. Capra, O. Bottauscio, D. Serazio
An electrode-matrix cell for electrolytic conductivity measurements
IEEE Transactions on Instrumentation and Measurement, Vol. 56, no. 2, pp. 321-325, 2007 (IF 0,832).

Preliminary results on the design and investigation of an electrode-matrix cell for electrolytic conductivity measurements are presented. A cell prototype has been conceived with the end of studying the electrical and current field behavior in aqueous solutions with different electrode configurations. The cell has been modeled using the boundary element method in order to obtain suitable cells for electrochemical measurements with computable constant. The calculated cell constants, corresponding to different configurations of the electrodes, were compared with the measured values. Measurements were performed on aqueous solutions with different ion concentrations while varying the supplied electrode configuration.

G. Durin, F. Colaiori, C. Castellano, S. Zapperi
Signature of negative domain wall mass in soft magnetic materials
Journal of Magnetism and Magnetic Materials, Vol. 316, pp. 436-441, 2007 (IF 1,704).

Magnetic properties of ferromagnetic materials often originate from domain wall motion, involving different damping mechanisms, an effective mass and various interactions with the surrounding media. In metallic materials, eddy current damping overwhelms inertia and thus the effect of the mass is usually neglected. We have recently reported experimental evidence that in soft metallic ferromagnets eddy currents yield an observable negative contribution to the effective domain wall mass. The weight of this mass is of the order of 10^-5 kg/m², much larger than the positive Doring mass (~10^-9 kg/m²). This negative effective mass is responsible for the leftward asymmetry of Barkhausen noise pulse shapes. In particular, this asymmetry depends on the pulse duration and it is found to encode important information on the characteristic time of the underlying domain wall dynamics. Only on long timescales the pulse shapes are symmetric and show the universal features typical of the Barkhausen effect. This result clarifies the general significance of pulse shape asymmetry commonly observed in systems showing a similar crackling noise, and contributes to better understand the microscopic phenomena responsible of magnetic hysteresis.

F. Fiorillo, C. Beatrice, O. Bottauscio, E. Patroi
Measuring the hysteresis loop of permanent magnets with the pulsed field magnetometer
IEEE Transactions on Magnetics, Vol. 43, no. 7, pp. 3159-3164, 2007 (IF 0,959).

We discuss a comprehensive approach to the characterization of permanent magnets with the Pulsed Field Magnetometer. It is based on a systematic comparison of the results obtained by this method with the ones provided by the conventional closed-circuit and open-sample methods and on the assessment of the dynamic phenomena engendered by the application of the fast exciting field pulse. Such phenomena descend from the thermal fluctuation aftereffect and the eddy currents, whose contributions to hysteresis loop swelling are brought to light and separately evaluated. It is thus shown that the quasi-static hysteresis loop can be retrieved from the dynamically obtained one by compensating for the magnetic viscosity field, found to be proportional to the coercive field, and the eddy current counterfield. The effect of the latter is predicted and accounted for by simple analytical formulation.

G. Ghigo, D. Andreone, R. Gerbaldo, L. Gozzelino, F. Laviano, G. Lopardo, B. Minetti, E. Monticone, G. Ummarino, E. Mezzetti
Effects of disorder on the performance of magnesium diboride microwave resonators
IEEE Transactions on Applied Superconductivity, Vol. 17, no. 2, pp. 3644-3647, Part 3, 2007 (IF 1,551).

A comprehensive understanding of the role of disorder in two-band superconducting magnesium diboride (MgB₂) is an essential requirement for its use in potential applications. Within this framework, we investigated the role of disorder in modifying the performance of MgB₂ microwave coplanar resonatoirs, characterized as a function of temperature and input power, before and after successive uniform irradiations with 250 MeV An ions. Also sample aging has been considered as a further source of disorder. We show the main features of the peculiar phenomenology concerning the effects of disorder on the electromagnetic response of the resonator, due to surface resistance reduction at low-temperatures and to non-monotonic residual resistance as a function of disorder level. The analysis is mainly focused on the nonlinear response of the device. These results are discussed in the framework of the two-gap model with significant interband scattering, taking also into account the grain-boundary network underlying polycrystalline films.

G. Ghigo, R. Gerbaldo, L. Gozzelino, F. Laviano, E. Mezzetti, E. Monticone, C. Portesi
Evidence of rf-driven dendritic vortex avalanches in MgB₂ microwave resonators
Journal of Applied Physics, Vol. 102, pp. 113901, 2007 (IF 2,171).

The influence of dendritic magnetic-flux penetration on the microwave response of superconducting magnesium diboride (MgB₂) films is investigated by a coplanar resonator technique. The characteristic feature consists of abrupt jumps in the resonance curves, which are shown to be induced by vortex avalanches freezing magnetic flux inside the resonator. Flux shaking provided by radio frequency currents is the origin of such avalanches, since a mechanism for magnetic instability of the dendrite type is local heating produced from flux motion. Once the external magnetic field has been changed, the interaction between microwave currents and flux lines influences the vortex-relaxation process. As a consequence, the vortex system is maintained close to a nonequilibrium state during the whole frequency sweep (few seconds), resulting in the observation of several events of dendrite nucleation and branching. From the analysis of a robust statistics, it results that avalanche-size distributions before and after flux-pinning tailoring by heavy-ion irradiation are fully consistent with a thermomagnetic model and with molecular dynamics simulations reported in literature.

G. Gubbiotti, M. Madami, S. Tacchi, G. Carlotti, M. Pasquale, N. Singh, S. Goolaup, A.O. Adeyeye
Field evolution of the magnetic normal modes in elongated permalloy nanometric rings
Journal of Physics: Condensed Matter, Vol. 19, p. 406229, 2007 (IF 1,886).

The eigenmode spectrum of elongated permalloy rings with relatively wide arms is investigated by combined Brillouin light scattering and ferromagnetic resonance measurements as a function of the applied field intensity, encompassing both vortex and onion ground states. To reproduce the frequencies and the spatial profiles of the measured modes we performed micromagnetic simulations which solve the discretized Landau-Lifshitz-Gilbert equation in the time domain and calculate locally the Fourier transform. This allowed us to correlate the field dependence of different modes to their localization inside different portions of the rings. With the rings in the vortex ground state, in addition to radial, fundamental, and azimuthal modes, a localized mode, existing in the element portions where the internal field assumes its minima, has been measured and identified. This latter mode, whose frequency decreases for increasing field intensity, becomes soft near the transition from vortex to onion state and determines the change in symmetry of the magnetic ground state. After the transition, it is replaced by two edge modes, localized on the internal and external boundary of the rings, respectively.

S.N. Kane, Zs. Gercsi, F. Mazaleyrat, L.K. Varga, A. Gupta, M. Coisson, P. Tiberto, F. Vinai, F. Celegato
Influence of annealing on high frequency magnetotransport properties of melt spun Fe₃₁Co₃₁Nb₈B₂₀alloy
Journal of Non-Crystalline Solids, Vol. 353, pp. 3099-3102, 2007 (IF 1,319).

The influence of furnace annealing and Joule heating on microstructure and high frequency magnetotransport properties of Fe₃₁Co₃₁Nb₈B₃₀ alloy has been studied using differential scanning calorimetry, hysteresis and Mössbauer spectroscopy measurements. Annealing reduces disorder in the specimens via structural relaxation improving soft magnetic properties. In as-cast specimens the spins preferentially remain within ribbon plane whereas annealing above 400 °C they become random. Magnetoimpedance shows a progressive deterioration of the magnetoimpedance response upon furnace annealing as well as Joule heating of the samples.

M. Kupferling, C. Appino, V. Basso, G. Bertotti, F. Fiorillo, P. Meilland
Magnetic hysteresis in plastically deformed low-carbon steel laminations
Journal of Magnetism and Magnetic Materials, Vol. 316, no. 2, pp. E854-E857, 2007 (IF 1,704).

Interstitial-free (IF) low carbon steel laminations have been subjected to plastic deformation either by tensile straining or cold rolling and their magnetic hysteresis behavior has been investigated for permanent elongation up to approximately 6%. Weaker magnetic hardening is observed, for a given strain level, in the cold-rolled (CR) materials, an effect chiefly ascribed to a more favorable profile of the residual stresses. Cold rolling leads to more homogeneous distribution of the internal compressive and tensile stresses compared to deformation by tension, and this results in a more uniform domain structure and softer magnetic behavior.

M. Kuepferling, C.P. Sasso, V. Basso, L. Giudici
An isothermal Peltier cell calorimeter for measuring the magnetocaloric effect
IEEE Transactions on Magnetics, Vol. 43, no. 6, pp. 2764-2766, 2007 (IF 0,959).

We have developed a method for isothermal calorimetry for the determination of the entropy change in magnetic materials. Heat absorbed and released by the sample at constant temperature is measured by means of Peltier cells, used in an active way to simultaneously measure the heat current and keep constant the sample temperature. In the paper we describe the method, the Peltier cell calibration and the test apparatus. The results obtained on a Gadolinium sample at room temperature under a magnetic field up to 0.9 T are discussed. The comparison with other methods demonstrates the validity of the proposed approach to fulfill the isothermal conditions (ΔT <= 5 mK) and to obtain a faster time response.

V. Lacquaniti, D. Andreone, N. De Leo, M. Fretto, S. Maggi, A. Sosso, M. Belogolovskii
Analysis of the temperature stability of overdamped Nb/Al-AlO_x/Nb Josephson junctions
IEEE Transactions on Applied Superconductivity, Vol. 17, no. 2, pp. 609-612, Part 1, 2007 (IF 1,551).

The temperature stability is one of the most important factors determining the successful application of the Josephson effect to the ac voltage standard or to analog and digital electronics. Whereas SIS hysteretic junctions with an Ambegaokar-Baratoff (A&B) behavior exhibit a reduced drift around the working temperature of the liquid helium, metallic-barrier SNS junctions follow a Kulik-Omelianchuck (K&O) behavior with a sharp temperature dependence of in this region. The objective of our research is to study this aspect for overdamped - heterostructures with current densities of 10-75 and characteristic voltages from 100 to more than 500 , that have been fabricated at INRIM. The characteristics, measured for Josephson heterostructures with different thickness, , and exposure, , essentially deviate from A&B and K&O curves, because of proximity effect caused by the comparatively high value of (up to 100 nm). We study theoretically two extreme limits: the clean and the dirty limit for the interlayer between the superconducting electrodes and discuss the temperature stability of the junctions characterizing it with the temperature derivative . The combined experimental and theoretical analysis of the problem provides a way for understanding, controlling and improving the design of the junctions in order to enhance their reliability.

V. Lacquaniti, N. De Leo, M. Fretto, S. Maggi, A. Sosso
Nb/Al-AlO_x/Nb Overdamped Josephson Junctions above 4.2 K for Voltage Metrology
Applied Physics Letters, Vol.91, no. 25, 252505, 2007 (IF 3,596).

The temperature dependence of the quantized voltage steps near the superconducting transition temperature of Nb/Al-AlO_x/Nb overdamped Josephson junctions irradiated at 75 GHz has been studied. These junctions can switch between the hysteretic and nonhysteretic regime either by varying a fabrication parameter or, as shown in the present paper, by changing the junction operating temperature. Due to the high values of JC and VC up to 75 kA/cm² and 0.5 mV at 4.2 K, respectively, and to the moderate temperature dependence of these parameters, the height of the first rf-induced step was larger than 1 mA at T=6-8 K, corresponding to 0.7-0.9T/TC on a junction of 5×5 µm². The flatness at the nanovolt level of this step demonstrates the feasibility of programable or ac voltage standards operating in a cryocooler setup.

M. Lo Bue, V. Basso, C.P. Sasso, G. Bertotti
Role of pressure and magnetic field in the magnetostructural phase transition of GdSiGe alloys
Journal of Magnetism and Magnetic Materials, Vol. 316, no. 2, pp. 361-363, 2007 (IF 1,704).

A thermodynamic treatment of field-driven magnetostructural phase transition in GdSiGe alloys is presented. Data from literature are described and discussed using a phenomenological equation of state. It is shown that the effect of magnetic field H and hydrostatic pressure p on the transition can be described by a single driving term consisting of a proper combination of (H; p; T).

A. Manzin
Element-free Galerkin modeling of electromagnetic phenomena in ferromagnetic deformable bodies
IEEE Transactions on Magnetics, Vol. 43, no. 4, pp. 1285-1288, 2007 (IF 0,959).

In this paper, the element-free Galerkin method is employed for evaluating eddy current distribution in ferromagnetic media, whose cross-section is subjected to an imposed time-dependent homothetic transformation and to a time-varying magnetic flux. A step-by-step procedure is used for handling the transient evolution. The extension to nonlinear and hysteretic media is realized adopting the fixed point scheme and the classical Preisach model.

A. C. Mills, M. B. Weissman, G. Durin
Use of the one-and-a-half-spectrum to determine Barkhausen noise asymmetry
Fluctuation and Noise Letters, Vol. 7, pp. L13-18, 2007 (IF 0,696).

We demonstrate the use of the one-and-a-half spectrum as a way of looking at the time-asymmetry of Barkhausen noise. This method is of particular value because it allows us to look in the regime where individual Barkhausen pulses are no longer distinguishable. We use the one-and-a-half spectrum on Barkhausen data from two different ferromagnetic samples and find asymmetries in the noise of both. The magnitude of the asymmetry is different in the two samples and we find no clear change in the asymmetry when we move from the regime of well-separated jumps at low field rate to the continuous fluctuating signal at higher rates.

E. Monticone, C. Portesi, S. Borini, E. Taralli, M. Rajteri
Superconducting MgB₂ nanostructures fabricated by electron beam lithography
IEEE Transactions on Applied Superconductivity, Vol. 17, no. 2, pp. 222-224 Part 1, 2007 (IF 1,551).

MgB₂ meander lines with width ranging from 250 to 500 nm have been fabricated by electron beam lithography (EBL)-based technique. Magnesium diboride films grown by all-in-situ method have been used. A critical current density of 8 MA/cm(2) was measured for meander with width down to 300 nm. For sake of comparison the measurements have been performed as well on 10 mu m wide strip patterned on the same sample. The results show that the nanostructuring process doesn't affect the superconducting properties of the structure. The flexibility of the EBL approach makes it interesting in view of fabrication of MgB₂ superconducting devices, such as photon detectors.

M. Pasquale, S. Perero, D. Lisjak
Ferromagnetic resonance and microwave behavior of ASn-substituted (A=Ni-Co-Zn) BaM-hexaferrites
IEEE Transactions on Magnetics, Vol. 43, no.6, pp.2636-2638, 2007 (IF 0,959).

ASn-substituted BaM-hexaferrites with compositions BaFe₁₂ 2_xA_xS_nxO₁₉, where A=Co, Ni, Zn, and x = 0 5-2, were synthesized using a solid-state reaction at 1100-1300 C. Hexaferrites formation was controlled by X-ray powder diffraction. The static magnetic properties were determined and the ferromagnetic resonance frequency of the powders was obtained using a vector network analyzer and a coplanar waveguide. It is shown that the degree of substitution (x) has a strong influence both on the static magnetic and the microwave behavior of the ceramics. Due to the changes in the anisotropy and saturation magnetization, the ferromagnetic resonance frequency shows a considerable decrease, from the 48 GHz for pure BaFe₁₂O₁₉, to about 10-20 GHz for samples with x ≈0.5, 1.

M. Pasquale, C. P. Sasso, L. Giudici, T. Lograsso, D. Schlagel
Field-driven structural phase transition and sign-switching magnetocaloric effect in Ni-Mn-Sn
Applied Physics Letters, Vol. 91, no. 13, art. no. 131904, 2007 (IF 3,596).

Depending on the starting equilibrium temperature, the application of a magnetic field on a sample of Ni-Mn-Sn produces sample heating or cooling during adiabatic experiments. The competition between endothermal and exothermal effects is observed close to the martensite-to-austenite magnetostructural phase transition. A model assuming the coexistence of two phases and a field dependence of their volume allows to compute the evolution of entropy and heat capacity during the phase transition. The correct fitting of the results suggests that the field-induced reduction of the martensite-to-austenite transition temperature is responsible for the observed sign switching of the magnetocaloric effect.

S. Perero, M. Pasquale
Microwave measurement uncertainty due to applied magnetic field
Physica Status Solidi A, Vol. 204, pp. 4062-4066, 2007 (IF 1,214).

In recent years there has been a wide interest in the production and analysis of films and nanostructures of different types for their microwave properties up to the mm-wave range. In order to characterize the electromagnetic behavior of these devices new experimental techniques need to be developed and assessed. Typically the measurements involve the use of vector network analyzer, and require several calibration steps. In this paper, we present a summary of the calibration techniques and evaluate the uncertainties obtained under different conditions, with a particular focus on the effect of the applied magnetic field upon uncertainty.

R. Piccin, P. Tiberto, G. Ababei, A.R. Yavari, M. Baricco
Influence of Nb and Y Additions on glass formation and magnetic properties in the Fe₇₈B₁₄Si₈ Alloy
Advanced Engineering Materials, Vol. 9, no. 6, pp. 480-482, 2007 (IF 1,463).

In the present work, the effect of small additions of Nb and Y to Fe₇₈B₁₄Si₈ alloy is analyzed concerning its glass forming ability and magnetic properties. Small ingots were obtained by injection casting method into a cylindrical Cu-mold. Different casting machines were used in order to evaluate the role of processing parameters on glass formation. Hysteresis loops have been measured using a vibrating sample magnetometer (VSM) and inductive methods. Structural properties were measured using differential scanning calorimetry and X-ray diffraction (XRD). The glassy phase is obtained only with both Nb and Y small addition (4 and 3 at. %, respectively). Moreover, a complete glassy phase with good soft magnetic properties is obtained only with the use of water cooled Cu-mold. In such case, the saturation magnetization is 0.91 T with a coercive field of 170 A/m.

R. Piccin, P. Tiberto, M. Baricco
Glass formation and magnetic characterization of (Fe₇₈B₁₄Si₈)-Nb-Y alloys
Journal of Alloys and Compounds, Vol. 434, pp. 628-632, 2007 (IF 1,455).

In the present work, the glass formation of Fe₇₈B₁₄Si₈ alloy with small additions of Nb and Y has been investigated. Ribbons were prepared by planar-flow casting. Small ingots (up to 5mm in diameter) were obtained by injection casting technique into a conical Cu mold. Thermal and structural properties were measured using differential scanning calorimetry (DSC) and X-ray diffraction (XRD), respectively. The microstructure has been observed by scanning electron microscopy (SEM). Quasi-static hysteresis loops have been measured using a vibrating sample magnetometer (VSM). Rapid solidification leads to a fully amorphous structure for all compositions. A partial amorphous structure has been obtained in samples prepared by copper mold casting, when adding Nb and Y. The role of Nb and Y addition on glass formation is discussed on the basis of melting behavior, analyzed by HT-DSC. Magnetic properties are correlated with the observed microstructures.

U. Pogliano, G. Boella, D. Serazio
An investigation Over Superconductive Inductive and Capacitive Capacitive Components for High Precision Measurements
IEEE Transactions on Instrumentation and Measurement, Vol. 56, no. 4, pp. 543-546, 2007 (IF 0,832).

Superconducting inductive and capacitive components seem to be very appealing for many high-precision measurements because of their reduced dissipation. Some tests made at Istituto Nazionale di Ricerca Metrologica have proved the possibility of building inductors with quality factor higher than several thousand in the acoustic frequency band using copper clad Nb-Ti wires. However, the best performances have been obtained with pure Nb wire, in spite of some connection problems.

U. Pogliano, G. C. Bosco, M. Lanzillotti
Calibration of a wideband transformer for measurement in the millivolt range by means of AC-AC transfer
IEEE Transactions on Instrumentation and Measurement, Vol. 56, no. 2, pp. 543-546, 2007 (IF 0,832).

This paper describes the development and calibration of a wideband transformer for precise measurements of ac voltage in the millivolt range. The output/input ratio and the sensitivity to load of the transformer are calibrated by means of ac-dc transfer standards for frequencies up to 1 MHz.

C. Portesi, S. Borini, G. B. Picotto, E. Monticone
AFM analysis of MgB₂ films and nanostructures
Surface Science, Vol. 601, no. 1, pp. 58-62, 2007 (IF 1,855).

For the fabrication of superconducting devices based on nanostructured thin films, the quality of the starting surface is often of crucial importance. For example, the transport properties of superconducting nanobridges are strongly affected by the geometry and the edge definition of the nanostructures. In this work, we report about AFM characterization of magnesium diboride films and nanobridges fabricated in view of application in superconducting electronics. MgB₂ films, obtained by co-deposition method followed by annealing in situ on silicon nitride substrate, have been nanostructured by electron beam lithography and ion milling. The analysis of the AFM images by the height-height correlation function shows that the films have a self-affine smooth textured surface with a RMS roughness of 20 nm. Furthermore, the nanobridges are continuous, with a well-defined geometry and a rounded profile, and the nanostructuration process does not significantly affect the film morphology.

C. Portesi, E. Taralli, R. Introzzi, M. Rajteri, E. Monticone
Fabrication and characterization of an MgB₂ bolometer
Superconductor Science and Technology, Vol. 20, pp. S403-S407, 2007 (IF 2,547).

In this work, we present the experimental results obtained in the fabrication and characterization of a superconducting MgB₂ bolometer. The device was made from an MgB₂ meander- like structure suspended on a 500 nm thick SiN membrane. The MgB₂ meander line was 50 mu m wide and 7.6 mm long and it was defined by optical lithography and dry etching. The SiN membrane had an area of 1.3 mm × 1.3 mm and it was obtained by a silicon micromachining technique. The electrical and thermal properties of the device were measured at low temperature in a closed- cycle cryocooler. The resulting T-c of the meander was unchanged with respect to the unprocessed film and the transport properties, measured in voltage- biased mode, indicated a value for J(c) of the order of 10⁵ A cm^-2 at 27 K. The logarithmic sensitivity of the bolometer turned out to be higher than 150. The study of the thermal properties of the bolometer on the membrane showed a thermal conductance of the order 10^-5 WK-1 at a working temperature of 32 K. The bolometer, irradiated by a chopped laser beam, showed a cut-off frequency of 94 Hz. The maximum experimental responsivity was estimated to be 2.3 × 10³ VW-1.

C. Ragusa, C. Appino, F. Fiorillo
Magnetic losses under two-dimensional flux loci in Fe-Si laminations
Journal of Magnetism and Magnetic Materials, Vol. 316, no. 2, pp. 454-457, 2007 (IF 1,704).

Magnetic energy losses have been measured in non-oriented Fe-Si laminations under alternating, elliptical, and circular polarization as a function of frequency (2 Hz ≤ f ≤ 200 Hz) and peak magnetization (0.2 T ≤ J_p ≤ · 1.7 T). The results have been analysed for each J_p value applying the concept of loss separation and investigating the evolution of each loss component with the shape of the flux loci. It is found that such an evolution is to a good approximation frequency-independent and it is a function of J_p and the ellipticity parameter only. This brings about substantial simplification in the phenomenological approach to the energy loss prediction under 2D magnetization process.

M. Rocchia, M. Ellena, G. Zeppa
Determination of ethyl alcohol content in red wines with an optical alcohol meter based on nanostructured silicon
Journal of Agricultural and Food Chemistry, Vol. 55, p. 5984, 2007 (IF 2,532).

A rapid analytical method for selectively monitoring ethyl alcohol in red wines without sample pretreatment, based on the use of an optical sensor, has been developed exploiting a porous silicon microcavity. The optical structure, realized by alternating layers of different porosities, was stabilized by thermal oxidation, and the resonant peak shift of the microcavity (projected at 600 nm) was monitored in the presence of more than 20 red wines. The resonant peak shows an increasing red shift depending on the wine alcoholic strength, which is ascribable to a change of refractive index due to physisorption/condensation of ethanol vapors inside the pores' structure. The linear response of the PS oxidized microcavity to the wine alcoholic strength insures the determination of the ethanol amount with a high accuracy and reliability. The calculated values differ by less than 0.5% to those obtained with the official method in accordance with the limits imposed by European laws. Moreover, a user-friendly interface, allowing the sensor to be used by unskilled persons, and portable packaging, able to ensure in situ measurements, have been developed.

M. Rocchia, A. M. Rossi, G. Zeppa
Determination of ethanol content in wine through a porous silicon oxide microcavity
Sensors and Actuators B - Chemical, Vol. 123, no. 1, pp. 89-93, 2007 (IF 2,934).

This paper reports on a new sensor, based on a porous silicon oxide microcavity, for the determination of the alcoholic strength of white and red wines. The shift of the cavity mode due to interaction with ethanol is monitored in continuous way by means of Fourier transform infrared (FT-IR) spectroscopy comparing the data obtained in condensation and evaporation mode. The results demonstrate the advantage of working in evaporation mode and the possibility to determine the alcoholic strength of wine with a good reproducibility and selectivity.

F. Shahri, A. Beitollahi, S.G. Shabestari, M. Ghanaatshoar, M.M. Tehranchi, S.M. Mohseni, S.E. Roozmeh, N. Wanderka, F. Fiorillo
Structural characterization and magnetoimpedance effect in amorphous and nanocrystalline AlGe-substituted FeSiBNbCu ribbons
Journal of Magnetism and Magnetic Materials, Vol. 312, no. 1, pp. 35-42, 2007 (IF 1,704).

Two series of rapidly solidified FINEMET (Fe_73.5Si_13.5B₉Nb₃Cu₁) alloys with and without partial substitution of Al (1.5 at%)/Ge (1 at%) were prepared by melt-spinning technique. The nanocrystallization process was carried out by the heat treatment of the as-spun ribbons at 560 ºC for 1 hour in a vacuum furnace. X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimeter (DSC), Mössbauer spectroscopy, and magnetoimpedance (MI) measurements were conducted on the as-quenched and heat reated alloys to investigate their structural and magnetic properties. The average crystallite sizes obtained for the heat-treated samples were in the range of 10^-12 nm as confirmed by our XRD and TEM data. The ultrasoft magnetic behavior observed for the Al/Gesubstituted nanocrystalline alloys was confirmed both by our magnetic data and magnetoimpedance ratio (MIR%) results. A twofold increase in the magnitude of the MIR% (99%) was observed for the Al/Ge-substituted nanocrystalline alloy against that of the pure FINEMET alloy (_48%) measured at 5.5 MHz. This is believed to be related to the decrease of the magnetocrystalline anisotropy as well as magnetostriction decline due to the Al substitution for Fe atoms in this nanostructured alloy.

C. Serpico, G. Bertotti, R. Bonin, I. D. Mayergoyz, M. d'Aquino
Power spectrum of current-induced magnetization dynamics in uniaxial nanomagnets
Journal of Applied Physics, Vol. 101, no. 9, Art. No. 09A507, 2007 (IF 2,171).

Nanomagnets with uniaxial symmetry driven by spin polarized currents are considered, in which anisotropy, applied field, and spin polarization are all aligned along the symmetry axis. Thermal fluctuations are taken into account by adding a Gaussian white noise stochastic term to the equation for the deterministic dynamics. The corresponding Fokker-Planck equation is derived and it is solved by using separation of variable and eigenfunction expansion techniques. From the solution of the Fokker-Planck equation, the autocorrelation function and the power spectral density of magnetization are computed. The position and the linewidth of the peaks in the power spectral density are discussed in detail.

C. Serpico, G. Bertotti, I.D. Mayergoyz, M. d'Aquino, R. Bonin
Effect of thermal fluctuations in spin-torque driven magnetization dynamics
Journal of Magnetism and Magnetic Materials, Vol. 316, no. 2, pp. E919-E922, 2007 (IF 1,704).

Nanomagnets with uniaxial symmetry driven by an external field and spin-polarized currents are considered. Anisotropy, applied field, and spin polarization are all aligned along the symmetry axis. Thermal fluctuations are described by adding a Gaussian white noise stochastic term to the Landau-Lifshitz-Gilbert equation for the deterministic dynamics. The corresponding Fokker-Planck equation is derived. It is shown that deterministic dynamics, thermal relaxation, and transition rate between stable states are governed by an effective potential including the effect of current injection.

A. Sosso, D. Andreone, V. Lacquaniti, V. Klushin, A. M. He, M. Klein
Metrological Study of YBCO Josephson Junction Arrays Integrated in a Fabry-Perot Resonator
IEEE Transactions on Applied Superconductivity, Vol. 17, no. 2, Part 1, pp. 874-877, 2007 (IF 1,551).

The application of High Temperature Superconductor Josephson junctions to voltage metrology is promising for many reasons, beyond the evident advantage of simplified cryogenics and reduced costs of the apparatus. Owing to their intrinsic non-hysteretic behavior, arrays of shunted bicrystal YBCO junctions are particularly interesting for the realization of an ac voltage standard with quantum accuracy. Moreover, shunted bicrystal YBCO junctions arrays are advantageous because of the reduced area of the junctions, the wide range of characteristic voltages, and large critical currents. However, some specific problems arise, like possible effects related to the higher operating temperature. Furthermore, fabrication technology sets tight constraints on the design of structures for the distribution of microwave currents along the array junctions. We investigated the step properties under millimeter wave irradiation at frequencies about 75 GHz of HTS junction and arrays prepared on bicrystal substrates having grain boundaries. High sensitivity techniques were adopted to evaluate the step flatness at nV level and assess the accuracy of the step voltage. A new method that makes use of an open resonator, was implemented to irradiate the array, providing synchronization of a large number of junctions.

A. Taralli, M. Rajteri, E. Monticone, C. Portesi
Development of superconducting single-photon detectors at INRIM
International Journal of Quantum Information, Vol. 5, nos. 1 & 2, pp. 293-298, 2007 (IF 0,568).

We are developing single-photon detectors employing superconducting-transition-edge sensors (TESs). TESs are fabricated both with Ti and proximity bilayers of Ti/ Au and the characteristics of the two films are compared. In the visible-near infrared spectral region, the photon absorption occurs directly in the film and the quantum efficiency of the detector is limited by the reflection losses at the film surface, which are around 60%. For many applications, like quantum cryptography, these losses are too high. In a previous paper [Nucl. Instr. Meth. A 559(2) (2006) 757 -759], we presented a way to reduce the detector reflectance for two projects based on the deposition of a few layers of amorphous silicon-nitrogen alloys. In this paper, we report some experimental data at low temperature relative to those projects. We will also show how to minimize the detector reflectance simultaneously for three telecommunication wavelengths and for a new continuum band.

P. Tiberto, P. Allia, M. Baricco, M. Coisson, F. Vinai
Magnetic and magnetotransport properties in metastable granular systems
Journal of Alloys and Compounds, Vol. 434, pp. 594-597, 2007 (IF 1,455).

A negative, isotropic magnetoresistance (MR) has been measured in a wide class of nanogranular magnetic materials produced by off-equilibrium techniques. The common feature of these magnetic systems is the granularity, either structural or magnetic, on the nanometer scale. In this work analogies and differences among magnetotransport effects observed in bi-metallic alloys, either in bulk or thin-film form, will be highlighted. In addition, the role and nature of interparticle interaction on magnetic and magnetotransport properties of nanogranular systems will be discussed.

P. Tiberto, P. Allia, F. Celegato, M. Coisson, F. Vinai, F. Albertini, F. Casoli, S. Fabbrici, L. Nasi, F. Bolzoni
Low-temperature magnetic softening by competing anisotropy compensation in a granular FePt-Ag multilayer
Journal of Magnetism and Magnetic Materials, Vol. 310, no. 2, pp. 2231-2233, Part 3, 2007 (IF 1,704).

A multilayered nanogranular film of nominal composition (Fe₅₃Pt₄₇)₂₈Ag₇₂ was deposited by RF sputtering on a MgO(1 0 0) substrate. The sample was annealed in situ to induce a perpendicular anisotropy. Magnetization loops were measured by alternating gradient magnetometry in directions perpendicular and parallel to the ?lm plane from 5 K to room temperature. Magnetoresistance measurements were performed in the 2-300 K temperature interval by a standard four-contact method (maximum field: 70 kOe). A negative giant magnetoresistance is observed at all temperatures; below 11.5 K a strong positive effect adds, which is ascribed to anisotropic magnetoresistance.

P. Tiberto, M. Baricco, E. Olivetti, R. Piccin
Magnetic Properties of bulk metallic glasses
Advanced Engineering Materials, Vol. 9, no. 6, pp. 468-464, 2007 (IF 1,463).

The discovery and large scale investigation of rapidly solidified alloys have brought to light in the last three decades a new scenario in basic and applied magnetism. With a range of composition and microstructural states unavailable to conventional materials, the rapidly quenched alloys have in fact demonstrated unprecented versatile properties, provide unique opportunities in applications and enlarged the domain of physical theories. In this paper, the basic magnetic features of two classes of magnetic bulk metallic glasses, soft and hard magnetic alloys, will be briefly highlighted.

P. Tiberto, M. Coisson, F. Vinai, P. Allia, O. Bretcanu, E. Verne
Magnetic relaxation in ferrimagnetic glass-ceramics obtained by co-precipitation at different temperatures
IEEE Transactions on Magnetics, Vol. 43, no. 6, pp. 2471-2473, 2007 (IF 0,959).

Magnetic induction hyperthermia is a promising technique aimed at the treatment of cancer cells; however, the ef?ciency of the heat release is determined by the magnetic stability of the system. Ferrimagnetic glasses composed of magnetite and hematite crystals in a glassy matrix were prepared by melting of commercial reagents. The time evolution of the magnetic remanence was studied by submitting each sample to a saturating field of 20 kOe for 300 s. After sudden removal of the magnetic field, the evolution of the magnetic remanence was recorded for times up to 5×10⁴ s. In all cases, the remanent magnetization exhibits a nonsaturating, monotonic decrease of its magnitude. The results are interpreted in terms of rearrangements of disordered magnetic volumes at interfaces between adjacent magnetite crystals.

F. Vinai, F. Celegato, M. Coïsson, P. Tiberto, F. Albertini, F. Casoli, S. Fabbrici, P. Allia
Effect of Ag addition on the magnetic and magnetoresistance properties of Fe₅₃Pt₄₇ films
Journal of Magnetism and Magnetic Materials, Vol. 316, no. 2, pp. E35-E39, 2007 (IF 1,704).

A granular Fe₅₃Pt₄₇ film and two (Fe₅₃Pt₄₇)-Ag multilayers were prepared by rf sputtering on heated MgO (1 0 0) substrates. The samples were annealed in situ to induce a perpendicular anisotropy. The topography and magnetic domain structure are studied by AFM/MFM imaging. Magnetization loops are measured by alternating gradient magnetometry in directions perpendicular and parallel to the ?lm plane from 5 K to room temperature. Magnetoresistance measurements are performed in the 2-300 K temperature interval by a standard four-contact method (maximum ?eld: 70 kOe). Ag addition hinders the formation of the perpendicular phase. A negative magnetoresistance is observed in all samples, pointing to a spin-dependent scattering effect from FePt nanoparticles.

F. Vinai, M. Coisson, F. Celegato, S. N. Kane, P. Tiberto
Influence of magnetostriction on high-frequency magnetotransport properties of current-annealed amorphous magnetic wires
Materials Science and Engineering A - Structural Materials Properties Microstructure and Processing, Vol. 449, pp. 468-471, 2007 (IF 1,457).

Selected samples with different magnetostriction constants λ_s have been submitted to current annealing (dc Joule heating) to relax internal stresses produced during fabrication and to induce circular anisotropy. High-frequency (30 MHz-6 GHz) giant magneto-impedance has been measured with a vectorial network analyzer. The variation of the characteristic impedance with the magnetic ?eld turns out to be a function of the thermal treatment and of the alloy's λ_s. In general, the magneto-impedance response is seen to be slightly improved by thermal treatments at low-frequency values.

C. Appino, F. Fiorillo, C. Ragusa
Loss decomposition under two-dimensional flux loci in non-oriented steel-sheets
Przeglad Elektrotechniczny, Vol. 83, pp. 25-30, 2007.

Energy losses have been investigated as a function of magnetizing frequency (DC - 200 Hz) and peak polarization value (0.25 T - 1.7 T) in non-oriented Fe-Si laminations under controlled alternating, elliptical, and circular flux loci. It is shown that, exploiting the concept of loss decomposition and the ensuing interpretative framework provided by the statistical theory of losses, a phenomenological approach to the energy loss prediction under two-dimensional fluxes can be formulated. The treatment conspicuously relies on the analysis of the excess loss component and its frequency dependence, which is observed to follow to a good approximation a law of the type W_exc œ f^1/2, whatever the flux loci. It is concluded that the behavior of the energy loss under elliptical flux can be predicted to a good approximation as a function of frequency, peak polarization, and degree of ellipticity by pre-emptive experimental determination of the energy loss under alternating field and circular polarization at selected frequencies.

S. Borini, M. Staiano, M. Rocchia, A.M. Rossi, S. D'Auria
Advanced Nanotechnological Approaches for Designing Protein-Based "Lab-on-Chips" Sensors on Porous Silicon Wafer
Recent Patents on DNA & Gene Sequences, Vol.1, p. 1, 2007.

In this article, we will review the more recent patented approaches related to the design and development of micro- and nano-patterns of biomolecules on solid substrates for the realization of innovative biochips, including inkjet and spotting technology, and Scanning Probe Methods In addition, we will report on some important patents based on the use of porous materials as substrates, exploiting the large specific surface for the design of highly sensitive biodevices. The main advantages and drawbacks related to each technological approach to the biochips fabrication will be pointed out, and future perspectives in the field will be discussed.

U. Pogliano, B. Trinchera
RMS Voltage Measuring System for Precise Evaluation Of Electrical Quantities
Metrology and Measurement Systems, Vol. 14 no. 4. pp. 555-562, 2007.

This paper is about a system for the measurement of RMS voltage. One or more of these systems can be employed as components for a wide range of applications for the measurement of electrical quantities in the field of electrical metrology. The first implementation has demonstrated its functionality and the possibility to reach a stability of the AC voltage measurement in a wide frequency range with an accuracy within 10 parts in 10⁶, limited only by the DC voltage accuracy of the DAC employed. A second implementation, now under investigation, aims at improving the accuracy of the system for high precision measurements.

M. Staiano, M. de Champdoré, S. Borini, A. M. Rossi, M. Rossi, S. D'Auria
New emergent nanotechnologies in medical and biochemical applications: advanced fluorescence protein-based nanosensors
Current Chemical Biology, Vol. 1, p. 3, 2007.

In this review we explore the advantages deriving from the use of either enzymes or binding proteins to develop non-consuming substrate fluorescence biosensors. We report on a novel approach to address the consumption of substrate by enzyme-based biosensors, namely the utilization of apo-enzymes as non-active forms of proteins, which through still able to bind the ligand yet cannot transform it into product. We also report recent studies in which fluorescence labelling of a naturally thermostable binding protein by a fluorescent probe allows a quantitative monitoring of glucose. Finally, we will illustrate a novel methodology based on the utilization of porous silicon chips that allows a nanotechnological approach to the realization of protein arrays for analyses of high medical and biochemical interest.

M. Zucca
An overview on passive magnetic shielding of power systems: modelling and experiments, from solid laminations to grid shields
Magnews, International Newsletter of U.K. Magnetic Society, pp 12-14, Autumn 2007.

This paper shows an overview on passive shielding by presenting the basic mitigation principles and some magnetic field mitigation examples accomplished on power systems. Energy distribution plants, like an underground cable line and a substation, are considered as well as a typical high power industrial device like a welding machine. This paper shows how the mitigation aim can be obtained by a suitable numerical code and by the use of pure conductive and/or ferromagnetic laminations. Grid shields are briefly presented in the end.

L. Brunetti, L. Oberto, M. Sellone
Guida alla taratura dei wattmetri RF
Tutto_Misure, n. 03, pp. 227-232, 2007.

I processi di taratura dei wattmetri operanti ad alta frequenza sono tuttora legati al concetto di misuratore bolometrico, una tipologia di strumento ormai presente solo nei laboratori nazionali in quanto usata nella realizzazione dei campioni primari di potenza. La letteratura specifica, facendo prevalentemente riferimento ai wattmetri bolometrici, sembra ignorare che le definizioni, le procedure e le tecniche di taratura messe a punto per questo tipo di strumento necessitano modifiche ed integrazioni prima di poter essere correttamente applicate ai misuratori di potenza basati su differenti principi di funzionamento. Questo articolo è un primo tentativo di fornire delle linee guida orientate alle tarature di wattmetri commerciali nel campo di frequenze che si estende da qualche kHz fino a 50 GHz. In particolare si pone l'attenzione su quegli aspetti tecnici di norma non sufficientemente considerati nella letteratura specialistica.

L. Callegaro, V. D'Elia
INRIM: metrologia delle piccole correnti in regime continuo
Tutto_Misure, n. 01, pp. 71-72, 2007.

L. Callegaro
Un secolo di elettronica
Tutto_Misure, n. 02, p. 173, 2007.

Conference Proceedings

V. Basso, M. Kuepferling, C. P. Sasso, L. Giudici, L. Martino
Thermo-electric calorimetry for the measurement of the magneto-caloric isothermal entropy change
Refrigeration Science and Technology Proceedings (A. Poredos and A. Sarlah, eds.) IIR/IIF, N. 2007-1, pp.177-184, 2007.

The entropy change in magnetic materials due to the applied magnetic field is determined employing a Peltier cell calorimeter. We develop the calorimetric method in oder to use the cells in an active way and to set isothermal conditions. In the paper we describe the constitutive equations of the Peltier cell as sensor and actuator, the calibration procedure and a measurement example.

V. Basso, C. P. Sasso, G. Bertotti, M. LoBue, L. Morellon, C. Magen
Predictions of AMR refrigeration cycles on Gd-Si-Ge alloys
Refrigeration Science and technology proceedings (A. Poredos and A. Sarlah, eds.) IIR/IIF, N. 2007-1, pp. 263-270, 2007.

The AMR refrigeration cycle is predicted for single crystals of the Gd₅ Si₂ Ge₂ compound with the maximum magnetic field of 2T and at a working temperature around 270K. The predictions are based on the hysteresis modeling of the magnetic-field-driven phase transformation. The results obtained by the model demonstrate that the presence of hysteresis changes the shape of the transformations, but it has no significant effect on the efficiency of the cycles.

M. Borsero, C. Pravato, A. Sona, M. Stellini, A. Zuccato
Improved adapters for the accurate calibration of LINS input impedance
Proceedings of the 18^th International Zurich Symposium on EMC, pp. 489-492, Munich (Germany), 24-28 September 2007.

The paper deals with the accurate calibration of the input impedance of the artificial mains network (the so-called LISN), focusing on the parasitic parameters at the EUT port and their effects on the LISN calibration. The goal is to improve the calibration accuracy and repeatability by adopting a standardized external adapter, used to connect the measurement system to the LISN. Different models are analysed, both theoretically and experimentally, through meaningful experimental examples.

L. Callegaro, V. D'Elia, J. Bohacek
Four terminal-pair impedance comparisons between INRIM and CTU
Instrumentation and Measurement Technology Conference Proceedings, pp. 1-5, 2007 IEEE.

Since forty years, it is known that four terminal-pair (4TP) definition permits to achieve the highest accuracy in impedance measurement. While for ac resistors and capacitors 4TP standard definition is commonplace, and 4TP commercial measurement systems are available on the market, for inductance two-or three-terminal definition is still the most common. In the following, we describe the first international intercomparison of inductance performed with 4TP measurement systems and a 4TP travelling standard of nominal value of 100 mH. Despite the difference in traceability and measurement techniques employed, results show a high degree of compatibility.

P. P. Capra, F. Galliana, M. Astrua
A 100 MΩ step hamon guarded network to improve the traceability level of high resistance up to 1GΩ
Proceedings of the 13^th International Metrology Congress, Lille (France), June 2007 (cd rom).

At INRIM, a 100 MΩ step Hamon guarded resistor was developed and metrologically validated. With it the traceability level of the maintained 1 GΩ at INRIM improve from 8×10^-6 to than 5×10^-6. The guarding system is a chain of 10 MΩ resistors. Main 100 MΩ resistors are surrounded by two metal rings driven to guard potentials so the leakage resistance in parallel with them is fragmented in three part. In two of these the leakage current is sensibly limited and the third portion is in parallel with guard resistors. Details of the development of the Hamon, stability data in parallel and series configurations and a metrological validation with DMM-Calibratorbased method and Dual Balance resistance bridge are given.

P. P. Capra, F. Galliana, M. Astrua, E. Gasparotto
Use of a 100 MΩ step Hamon resistor for calibration of pico-ammeters in dc current in the range 100 pA ÷ 100 nA
Proceedings of the 15^th IMEKO TC4 Symposium on Novelties in Electrical Measurements and Instrumentation, Iasi (Romania), September 2007 (cd rom).

This paper describes a measurement circuit for the calibration of pico-ammeters in dc current. The system is based on a 100 MΩ Hamon network developed at INRIM to improve the traceability level of the maintained 1 GΩ standard. Besides the Hamon network, the measurement system, presented in this paper, consists of a precision dc voltage source and an electronic circuit used as voltage guard driver.

G. Crotti, A. Sardi, N. Kuljaca, P. Mazza, G. de Donà
Set up and characterization of reference measuring systems for on-site live verification of HV instrument transformers
Proceedings of the 13^th International Metrology Congress, Lille (France), June 2007 (cd rom).

Prototype reference measuring systems (RMS) for the on-site verification of high voltage instrument transformers for energy metering have been set up. Their use can make possible the identification, without service removal, of the current and voltage transformers which no longer comply with the accuracy requirements. Specific measurement procedures have been experimented in the characterisation of the RMSs, which include as reference transducers a Rogowski coil and a resistive-capacitive divider for the current and voltage measurement respectively. The uncertainty associated with the on-site use of the RMSs is evaluated considering the operating conditions which are likely to occur. The results obtained in the first tests carried out show the feasibility of a live, on-site accuracy check of the instrument transformers.

V. Lacquaniti, A. Sosso, D. Andreone, S. Maggi, N. De Leo, M. Fretto, C. Portesi, S. Borini, M. Rajteri, R. Rocci, E. Monticone
Quantum devices for voltage metrology and photon counting
Workshop NanoMetrology 2007 - Metrology for Nanotechnology, Torino, June 2007. Published in nanotech IT Newsletter, pp. 4-7, June 2007.

The activity on quantum micro and nanodevices for metrology developed at INRIM has contributed to the development of Josephson junctions for new voltage standards and of high quality detectors for photon counting. In the following we report on some properties of Nb/Al-Alo_x/Nb overdamped junctions which can be useful to overcome some basic problems of state of the art Josephson array circuits and of MgB₂ devices for mid superconducting electronics. In particular the high values of critical current density and characteristic voltage, together with the temperature dependence of the overdamped junctions look promising for the realization of improved devices for programmable and AC voltage standard, where a simple fabrication process, a moderate number of junctions and the possible use of cryocoolers with reduced power dissipation can open the employ of these standards to a more widespread employ than for primary metrological institute. On the other hand the discovery of superconductivity at 39 Kº in MgB₂ offers the possibility of a new class of high-speed superconducting electronic devices due to their favorable combination of higher critical temperature than conventional BCs superconductors and a symmetric order parameter with a large superconducting gap.

V. Lacquaniti, D. Andreone, M. Fretto, N. De Leo, S. Maggi, F. Francone, R. Rocci, D. Serazio, A. Sosso
Overdamped Josephson Junctions for Applications to Precision Measurement
Proceedings of 2^nd International Workshop on Advances in Sensors and Interfaces IWASI 2007, pp. 265-268, Bari (IT), June 2007.

Overdamped Nb/Al­AlO_x/Nb Josephson junctions are an intermediate state between the SIS and SNS Josephson junctions. With a proper choice of the fabrication parameters, stable and reproducible nonhysteretic current­voltage characteristics have been obtained. Featuring critical current densities up to 70 kA/cm² and characteristic voltages up to 450 µV at 4.2 K, overdamped junctions are suitable for many applications ranging from RSFQ electronic circuits to programmable and ac voltage standards. Tests on single junctions and arrays of series­connected junctions have shown a suitable behaviour when driven by a microwave with frequencies around 75 GHz. The quantized steps have proven to be stable and flat at nV level. These junctions have also shown an improved temperature dependence which can be interesting in view of different measurement applications.

V. Lacquaniti, D. Andreone, C. Cassiago, N. De Leo, M. Fretto, S. Maggi, A. Sosso, M. Belogolovskii
Nb-based overdamped junctions with improved performance for application to measurement
EUCAS 2007 Conference Proceedings, Bruxelles (Belgio), September 2007.

Optimization of the performance of Nb-based overdamped Josephson junctions for applications to superconducting electronics is a ma jor issue today. The use of cryocoolers, thus avoiding liquid helium refrigeration, with junctions working at temperatures higher than 4.2 K, could greatly increase the use of these devices in applications such as fundamental metrology and measurement sensors. The question we address here is how to maximize the characteristic voltage and minimize the temperature influence on the current-voltage curves of overdamped junctions enabling their use at T > 4.2K. To optimize the properties of a single Josephson heterostructure, we propose a type of overdamped junction that consists of a relatively thin insulating layer and a thick (tens of nm) normal-metal film between two superconducting electrodes. Measurements of the dependence of the critical current and characteristic voltage as function of temperature for different electrodes configurations show how it is possible to improve the design of these junctions.

S. Maggi, N. De Leo, M. Fretto, V. Lacquaniti, A. Agostino, P. Verhoeve
Superconducting Tunnel Junction X-Ray Detector with Ultra-Low Subgap Current
Proceedings of 2^nd International Workshop on Advances in Sensors and Interfaces IWASI 2007, pp. 243-248, Bari (Italy), June 2007.

Superconducting tunnel junctions are promising as radiation detectors because of their larger energy resolution with respect to conventional Si-based detectors. We have developed a fabrication process for Nb-based STJ devices which allows to fabricate junctions with leakage currents well below 50 pA at 300 mK, a factor of 10^-6 less than the leakage current at 4.2 K. The junctions are diamond-shaped with areas between 20 × 20 and 100 × 100 µm ². We report the details of the fabrication process, together with an analysis of the structure of films by AFM, SEM and x-ray spectroscopy. We show the measured I - V curves at 300 mK, together with preliminary results on x-ray measurements at 300 mK with a 5 mC 55 Fe source.

U. Pogliano, G. C. Bosco, M. Lanzillotti
Compensation of a Wide-band Transformer for Generation of Calibrate ac Voltages in the Millivolt Range
Proceedings of IMTC 2007, Warsaw (PL), May 2007 (cd rom).

The paper describes some load compensation circuits for a wide-band transformer employed in precise measurements of ac voltages in the millivolt ranges, for frequencies up to 1 MHz. By means of these circuits the load sensitivity of the transformer is reduced, so allowing the generation of precise ac voltages.

U. Pogliano, G. C. Bosco, M. Lanzillotti, D. Serazio
Ac-dc transfer standard shunts for frequencies up to 1 MHz
Proceedings of the 15^th IMEKO TC4 Symposium on Novelties in Electrical Measurements and Instrumentation, Vol. 1, pp. 232-237, Iasi (Romania), September 2007 (cd rom).

A new type of coaxial shunt for high frequency ac-dc current transfer standards has been designed. The structure of the shunts with nominal current from 100 mA to 5 A are made of a disk with two coaxial conductive layers in one side. SMD resistors are soldered in parallel between the two layers. Two conductive screens are applied in both side of the disk. In order to reduce stray effects, the structure has ideally no common magnetic interaction between the input current and the output voltage and practically a very low section where the magnetic field is confined, so allowing a flat response in a wide frequency range.

U. Pogliano, B. Trinchera
RMS Voltage Measuring System for Precise Evaluation of Electric Quantities
Proceedings of the 15^th IMEKO TC4 Symposium on Novelties in Electrical Measurements and Instrumentation, Vol. 1, pp. 132-136, Iasi (Romania), September 2007 (cd rom).

This paper is about the design and the construction of a system for the measurement of the RMS voltage. One or more of these systems can be employed as building blocks for a wide range of applications in the field of electrical metrology. The first implementation demonstrated its functionality and the possibility to reach a stability of the AC voltage measurement in a wide frequency range with an accuracy within 10 parts in 10⁶, limited only by the DC voltage accuracy of the DAC employed.

M. Rocchia, S. Borini, A. M. Rossi, S. D'Auria
Direct writing of a protein microarray - Lab on a chip for multipurpose sensing
Ultrasensitive and single molecule detection technologies II, edited by J. Enderlein, Z. K. Grycznski, Proceedings of SPIE, Vol. 6444, p. 64405, 2007.

A protein microarray has been realized on a porous silicon (PS) chip by means of electron beam irradiation using a standard SEM equipped with a nanopattern generator system. Two proteins have been used to generate the array: the glucose-binding protein (GBP) and the glutamine-binding protein (GlnBP), both isolated from Escherichia coli. The proteins functionality has been tested by means of a competitive assay.

B. Trinchera, L. Callegaro, V. D'Elia
Quadrature Bridge for R-C Comparisons based on Polyphase Digital Synthesis
IEEE Instrumentation and Measurement Technology Conference Proceedings, pp. 1-4, 2007.

A coaxial quadrature bridge based on digital synthesis has been developed. The bridge compares two resistance standards (having nominal resistance R), with two capacitance standards (nominal capacitance C), at an angular frequency omega(such that omega RC ~ 1). All standards are defined as two terminal-pair impedances. All voltages and currents employed in the bridge are generated by a multiphase direct digital synthesizer, constructed around a personal computer DAC board and a set of integrated amplifiers; the number of electromagnetic devices has been kept to a minimum. The bridge is made to be employed in the realization of the farad unit, starting from the representation of ohm given by the quantum Hall effect. Relative bridge accuracy during the calibration of 1000 pF capacitors in terms of 100 kOmega resistors at omega =10 kradmiddots^-1 has been verified to be less than 10^-6; preliminary uncertainty assignment give a transfer uncertainty of a few parts in 1^-7.

E. Vremera, L. Brunetti, E. Sfartz, L. Oberto, M. Sellone
Microcalorimeter techniques with thermoelectric transfer standards
Proceedings of the 15^th IMEKO TC4 Symposium on Novelties in Electrical Measurements and Instrumentation, Iasi (Romania), September 2007 (cd rom).

The paper describes the realization process of the high frequency power standard with a twin broadband microcalorimeter designed for effective efficiency measurement of power sensors based on thermocouples. The process includes the important step of the microcalorimeter self-calibration and auxiliary S-parameter measurements necessary for evaluating the system error correction. Besides the previously used microcalorimeter measurement techniques, this paper proposes a measurement method able to lead to the final result overpassing the corrections step or the use of the extrapolated values.

G. Basso, G. Crotti, A. De Lorenzo, D. Festa
Accreditamento SIT della grandezza "Campo Magnetico" da 10 Hz a 100 kHz
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

M. Borsero, C. Pravato, A. Sona, M. Stellini, A. Zuccato
Miglioramento delle caratteristiche di impedenza di modo comune delle LISN e del relativo metodo di taratura
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

Nel lavoro vengono esaminate le principali cause di incertezza nella misura dell'impedenza di ingresso Z_indi una rete artificiale (LISN), prevalentemente legate alla presenza di fenomeni parassiti. L'obiettivo è di individuare accorgimenti circuitali che consentano di ottimizzare la ripetibilità e l'accuratezza di misura. A tale scopo, sono state effettuate simulazioni e misure in configurazioni diverse, con connettori sia di uso commerciale sia appositamente realizzati per limitare gli effetti parassiti al variare della frequenza.

M. Borsero, G. Vizio, L. Anglesio, A. Benedetto
Un metodo per la valutazione del guadagno d'antenna in camera anecoica mediante analizzatore vettoriale di reti
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

Il lavoro descrive un metodo per la valutazione del guadagno d'antenna in camera anecoica mediante l'uso di un analizzatore vettoriale di reti (VNA). I risultati ottenuti con il metodo proposto sono confrontati con i valori forniti dal Two-Antenna Power-Gain method usualmente utilizzato. Rispetto a tale metodo il VNA presenta alcuni vantaggi, quali minor costo per l'allestimento della catena di misura, maggiore velocità, possibilità di effettuare un elevato numero di punti in frequenza (grazie alla modalità operativa a scansione del VNA). Nella seconda parte del lavoro vengono presentati e confrontati i risultati di una serie di misure di guadagno effettuate con VNA nelle camere anecoiche dell'INRIM e dell'ARPA su antenne del tipo open-ended guide e pyramidal horn nell'intervallo di frequenza da 450 MHz a 3 GHz.

M. Borsero, G. Crotti, L. Zilberti
Taratura in cella TEM di misuratori di campo elettrico a bassa frequenza
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 7-8, Torino, settembre 2007.

Le celle TEM possono essere utilizzate per la generazione di campi di riferimento a frequenza industriale o nella gamma delle frequenze acustiche, in alternativa ai sistemi a piastre piane e parallele. I vantaggi dell'utilizzo della cella TEM sono rappresentati dal più contenuto ingombro, dal minor costo e dal più elevato grado di protezione da interferenze con l'ambiente circostante. Per contro, l'ampiezza dei valori di campo generati è limitata e l'incertezza di misura associata a una taratura in cella TEM è superiore di circa un ordine di grandezza a quella relativa al sistema a piastre piane e parallele. Tale degrado delle prestazioni è dovuto essenzialmente alla forma ed alle dimensioni degli elettrodi, che danno luogo ad una distribuzione di campo che si discosta dal livello di uniformità ottenuto con i sistemi a piastre. Nel lavoro sono presentati i risultati di un'indagine comparativa, sperimentale e numerica, in cui sono stati analizzati un sistema a piastre piane e parallele e una cella TEM disponibili presso l'INRIM.

M. Borsero, A. Sardi, G. Vizio
Metodi di taratura per generatori di scariche elettrostatiche
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 227-228, Torino, settembre 2007.

La taratura dei generatori di scariche elettrostatiche (ESD) è essenziale per assicurare l'equivalenza e la riproducibilità delle prove realizzate da laboratori diversi. Le due procedure di prova (scarica a contatto e scarica in aria) previste dalla normativa impongono la messa a punto di due distinti metodi di taratura. Per rispondere alle esigenze dei laboratori di prova, l' INRIM ha predisposto un banco per la taratura dei generatori ESD. Per la misura della corrente di scarica si è caratterizzato uno "shunt" coassiale abbinato ad un oscilloscopio con banda passante da 2 GHz. Per la misura della tensione di carica del condensatore si è realizzato un partitore di tensione resistivo con resistenza di ingresso di 10 GΩ e rapporto di partizione 1/10000, abbinato a un multimetro ad alta risoluzione. La procedura di taratura del sistema di misura costituito dal partitore e dal multimetro prevede la determinazione del fattore di scala a 1000 V, realizzata alimentando il partitore con un calibratore per bassa tensione, e la verifica della linearità in tensione nel campo da 1 a 25 kV per confronto con il campione di rapporto in alta tensione continua dell'INRIM.

L. Brunetti, L. Oberto, P. Terzi, M. Sellone
Valori di Consenso nel primo confronto nazionale inter-laboratorio potenza in alta frequenza (SIT.AF-01)
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

Il Servizio di Taratura in Italia (SIT), allo scopo di verificare le capacità dei laboratori accreditati nel campo delle misure in alta frequenza (AF), ha promosso un Confronto Nazionale (SIT.AF-01) riguardante la potenza nelle bande di frequenza coperte dalle linee di trasmissione in coassiale da 7 mm (50 MHz - 18 GHz) e da 3.5 mm (50 MHz - 26.5 GHz). Al confronto hanno partecipato 12 laboratori di cui 10 effettivamente accreditati per le misure di potenza AF.

L. Brunetti, L. Oberto, M. Sellone
Innovazioni all'INRiM della tecnica microcalorimetrica in alta frequenza
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 9-10, Torino, settembre 2007.

Nel presente lavoro vengono descritte le innovazioni che sono state apportate alla tecnica microcalorimetrica utilizzata presso il Laboratorio di Alta Frequenza dell'INRiM per la realizzazione del campione di potenza. I cambiamenti permetteranno di lavorare con precisione e stabilità di temperatura migliori di quelle attuali. L'utilizzo, poi, di termopile più efficienti consentirà di aumentare la sensibilità del sistema. E' stato, inoltre, sviluppato un modello matematico più dettagliato che consente di tenere in conto contributi sistematici rivelatisi non trascurabili. Infine è anche presentato il progetto di un Convertitore Termico di tipo Calorimetrico che si sta attualmente sviluppando e che verrà utilizzato come campione di potenza per le basse frequenze, in particolare al di sotto dei 10 MHz, dove la tecnica microcalorimetrica classica risulta ancora poco efficace per difetto di sensibilità, nonostante i miglioramenti proposti.

F. Cabiati
Il sistema internazionale delle unità (SI) tra evoluzione e rivoluzione
Atti della XXVI Giornata della Misurazione, Padova (Italy), luglio 2007, 20 pp.

Una rapida analisi dell'evoluzione subita dall'unità di misura mette in luce come i cambiamenti abbiano interessato di volta in volta aspetti diversi, che vanno dal tipo di definizione, alla relazione tra definizione e campione primario, al tipo di riferimento adottato. Con la strutturazione delle unità in un sistema coerente quale l'SI, la definizione dell'unità acquista una valenza in più, in quanto garantisce una riferibilità generalizzata estesa anche alle misure indirette, assai importanti nella pratica scientifica, e le definizioni di unità che assumono come riferimento una costante fondamentale sono particolarmente adatte a questo ruolo. Appare quindi giustificato il forte impulso dato di recente alla ridefinizione di alcune unità, a partire da quella di massa, per riferimento a costanti fisiche il cui valore viene implicitamente o esplicitamente fissato. Fino a questo punto, i cambiamenti proposti e le azioni intraprese si collocano nella linea di evoluzione del sistema, pur segnando un'accelerazione del tutto inusuale. Di rivoluzione si potrebbe invece parlare se venissero poste in atto anche le ulteriori modifiche già da tempo autorevolmente proposte, che costituirebbero una ristrutturazione radicale del sistema di unità su basi razionali e di assai lunga durata. Esse riguardano sia la struttura dell'SI, ponendo sullo stesso piano le attuali unità di base e quelle derivate, sia le definizioni delle unità, sostituite dall'unica condizione imposta per la loro realizzazione: la consistenza con i valori fissati per le costanti assunte a riferimenti del sistema.

F. Cabiati
Dispositivi di collegamento quasi ideali con linee multicoassiali. Applicazione a campioni di ammettenza
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 11-12, Torino, settembre 2007.

Una ricerca sistematica aveva identificato nel cavo con quattro conduttori coassiali (tetrassiale) la struttura adatta a trasmettere tensioni e correnti con alterazioni trascurabili anche nelle misure ai più alti livelli di precisione (parti su 10^-9) per frequenze nel campo dei kilohertz. Per l'applicazione a campioni di ammettenza definiti con quattro porte coassiali, sono state poi sviluppate strutture di collegamento attive, basate sul cavo tetrassiale, in grado di fornire l'energia attiva e reattiva assorbita sia dalla linea di collegamento che dal carico, mantenendo così la condizione di funzionamento a vuoto per i generatori di tensione e di corto circuito per i generatori di corrente. La ricerca tuttora in atto tende a superare le limitazioni di frequenza imposte dalla condizione, fin qui assunta, che gli spezzoni di linea siano molto più corti della lunghezza d'onda corrispondente alla frequenza di lavoro. Nelle soluzioni individuate, la propagazione avviene simmetricamente dalle estremità verso il centro della struttura, dove le grandezze propagate (tensioni o correnti) sono mantenute uguali da un controllo operante in retroazione. In queste condizioni, la grandezza di riferimento è riprodotta sul carico con incertezza trascurabile anche in misure di alta precisione, entro limiti di frequenza imposti solo dalla banda passante del controllo attivo.

P. P. Capra, F. Galliana, D. Serazio
Miglioramento dei livelli di riferibilità nell'alta resistenza in corrente continua per mezzo della realizzazione di un resistore del tipo Hamon 10 × 100 MΩ automatizzato e dotato di guardia attiva
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

Negli anni scorsi all'INRiM, per le necessità di maggiore accuratezza, è stata compiuta una revisione della scala metrologica relativa alle alte resistenze: in particolare è stato sviluppato un sistema di misura basato su un multimetro e un calibratore per la taratura di resistori campione nel campo 10 Mohm ÷ 1 Tohm [1]. Questo metodo di misura è adatto a realizzare tarature automatiche di resistori di elevato valore per studiare il loro comportamento vs. la tensione applicata e per assicurare il trasferimento della riferibilità ai laboratori secondari. Alcuni Istituti metrologici hanno sviluppato dei sistemi di misura molto accurati [3, 4]. Presso l'INRiM, per migliorare i livelli di riferibilità a livello di 1 Gohm, è stato progettato e realizzato un resistore Hamon 10×100 Mohm con un sistema di guardia attiva che consente di definirlo nella configurazione a tre terminali [2]. Con questo campione si potranno migliorare i livelli di riferibilità del campione da 1 Gohm dell'INRIM dagli attuali 8×10^-6 a meglio di 5×10^-6. Inoltre questo progetto è adatto a campioni Hamon di valore più elevato allo scopo di estendere la riferibilità fino a valori di 10 Tohm e 100 Tohm e allestire un metodo di misura per la taratura di picoamperometri.

P. P. Capra, F. Galliana, M. Astrua, E. Gasparotto
Taratura di pico-amperometri in corrente continua nel range 100 pA ÷ 10 nA mediante uso di un resistore Hamon 10×100MΩ dotato di guardia
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 13-14, Torino, settembre 2007.

C. Cherbaucich, N. Kuljaca, P. Mazza, G. Crotti, A. Sardi, G. De Donà
L'accuratezza dei trasduttori di misura in AT: verifica in campo e sotto tensione
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

G. Crotti, D. Giordano, A. Agosto
Misura di campi magnetici ambientali con forme d'onda non sinusoidali
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

V. D'Elia, L. Callegaro
Realizzazione di un sistema di taratura di picoamperometri per correnti comprese tra 100 fA e 100 pA
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

V. Lacquaniti, D. Andreone, M. Fretto, N. De Leo, S. Maggi, C. Cassiago, F. Francone, R. Rocci, D. Serazio, A. Sosso
Giunzioni Josephson overdamped per applicazioni al campione di tensione programmabile
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 417-418, Torino, settembre 2007.

Negli ultimi anni la ricerca su nuovi campioni quantistici in grado di generare tensioni AC ha notevolmente aumentato l'interesse per le giunzioni Josephson con caratteristica tensione-corrente (I-V) non isteretica. La proprietà principale di queste giunzioni è la possibilità di selezionare velocemente ed indipendentemente dei "gradini" di tensione che risultino quantizzati in un adeguato intervallo di valori di corrente. Il progetto delle giunzioni dipende tuttavia dallo schema di misurazione, dato che esistono diverse soluzioni tecnologiche tra le quali: "potenziometri programmabili" che sfruttano un segnale in microonda di tipo sinusoidale, ovvero "sintetizzatori di forma d'onda arbitraria" che sono invece basati su codice a impulsi ad alta frequenza, trasmesso con un cavo coassiale. In quanto segue analizziamo le proprietà interessanti per applicazioni ad un campione AC di un tipo specifico di giunzioni Josephson "overdamped", ovvero le giunzioni Nb/Al-AlO_x/Nb, recentemente sviluppate all'INRiM.

G. La Paglia, G. C. Bosco, M. Lanzillotti
L'effetto della messa a punto negli strumenti di misura elettronici multifunzione
Atti del V Congresso Metrologia & Qualità, Torino, marzo 2007 (cd rom).

B. Trinchera, V. D'Elia, L. Callegaro
Ponti di impedenza a sintesi digitale per la realizzazione del farad dall'ohm
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 29-30, Torino, settembre 2007.

U. Pogliano, C. G. Bosco, M. Lanzillotti
Generazione di tensioni alternate a livello del millivolt mediante un trasformatore a larga banda compensato
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 31-32, Torino, settembre 2007.

In questo articolo sono descritti alcuni circuiti per la compensazione del carico operanti in una banda di frequenze fino ad 1 MHz. Mediante tali circuiti viene ridotta la sensibilità al carico di un trasformatore, permettendo la generazione di tensioni alternate più precise.

U. Pogliano, B. Trinchera
Sistema di misura di precisione della tensione alternata applicabile alla determinazione di grandezze elettriche
Atti del XXIV Congresso Nazionale Associazione "Gruppo Misure Elettriche ed Elettroniche" (GMEE), pp. 71-72, Torino, settembre 2007.

Il progetto e la costruzione di un sistema per la misura del valore efficace della tensione sono oggetto di questo articolo. Questo sistema può essere impiegato come elemento di base per la costruzione di numerosi sistemi nel campo della metrologia delle grandezze elettriche. La prima implementazione ne dimostra la funzionalità e la possibilità di raggiungere una stabilità della misura della tensione alternata in un'ampia banda di frequenze e con un'incertezza migliore di 10 parti in 10⁶, limitata solo dall'incertezza della tensione continua prodotta dal DAC impiegato.

Book Chapters

C. Serpico, G. Bertotti, I.D. Mayergoyz, M. d'Aquino
Nonlinear magnetization dynamics in nanomagnets
Handbook of Magnetism and Advanced Magnetic Materials, Kronmuller and Parkin, Eds. Wiley, 2007.

The theoretical study of magnetization dynamics has been the focus of considerable research for many years. Traditionally, this study has been driven by the ferromagnetic resonance problems in which the main part of magnetization is pinned by a strong constant magnetic field, while only a small transverse component of magnetization executes resonance motions caused by radio-frequency fields. These small magnetization motions are studied by linearizing the magnetization dynamics equation and, for this reason, the literature on magnetization dynamics has been mostly concerned with the linear magnetization dynamics studies. Recently, new directions of research have emerged that deal with large motions of magnetization and require the analysis of the nonlinear dynamics magnetization. This new directions are mainly connected to the recent advance in magnetic storage technologies. In this chapter, we will systematically apply and review the methods and concepts of nonlinear dynamical system theory relevant to the analysis of large magnetization motions governed by the Landau-Lifshitz equation. Sections II and III deal with the theoretical aspects of Landau-Lifshitz dynamics. First, the Landau-Lifshitz equation is introduced and its general property are considered. Then, Landau-Lifshitz dynamics is treated as a nonlinear dynamical system defined on a sphere and the problem of equilibria and geometric representation of dynamics is discussed. Special attention is paid to the conservative Landau-Lifshitz dynamics and detailed analytical expressions are derived for this dynamics in terms of elliptic-type integrals. Sections IV deal with precessional and damping magnetization switchings. Analytical treatment of the damping switching and the precessional switching for uniaxial magnetic particle is illustrated in details. Then, magnetization relaxation to equilibrium is analyzed by the averaging technique, resulting in a differential equation for the free energy. In Section V, we will address the problem of the existence of spatially uniform magnetization modes under far-from-equilibrium conditions driven from an external radio-frequency field. In the case of systems with uniaxial rotational symmetry subject to a circularly polarized radio-frequency field, the presence of rotational symmetry has far-reaching consequences because the equivalent dynamical system on the unit sphere is reduced to autonomous form and the basic physical aspects of the dynamics can be recast into corresponding topological and geometric properties of the phase portraits of the Landau-Lifshitz equation. The phase portraits of the dynamics and the associated bifurcation diagrams exhibit an extremely rich and structure, and provide some nontrivial predictions concerning periodic and quasi-periodic types of dynamical response as well as nonlinear ferromagnetic resonance mechanisms.

Technical Reports and Reports for Research Contracts

M. Astrua, P. P. Capra, F. Galliana, F. Francone, E. Gasparotto, D. Serazio
Rete Hamon per il trasferimento della riferibilità da 10 MΩ a 1 GΩ
Rapporto Tecnico INRIM n. 63, novembre 2007.

Presso l'INRIM nell'ambito del continuo processo di miglioramento dell'accuratezza di misura e di studio di nuove tecniche di misura nel campo dei resistori di alto valore, è stato progettato e costruito un prototipo di rete Hamon con dieci resistori da 100 MΩ. Le due configurazioni, serie e parallelo, consentono di effettuare un trasferimento di riferibilità dal valore di 10 MΩ a 1 GΩ con una misura semplice e che richiede solo un multimetro a 8 digits e un resistore campione da 10 MΩtarati. Nel rapporto tecnico è fornita la descrizione completa dell'intero progetto costruttivo e di tutte le prove e le misure che sono state effettuate per la caratterizzazione del dispositivo.

F. Bellotti, G. Amato
Reactive Ion Etching (RIE)
INRIM Technical Report no. 67, October 2007.

In this technical report we described the RIE's technic with a little view about plasma physics and other dry etching methods, a RIE instrument's manual is enclosed because all system was planned and assembled inside institute.

C. Boveri, L. Callegaro, F. Durbiano
EUROMET Electrochemical Analysis WG - Project: 918. Study on the traceability of salinity measurements in seawater. INRIM Measurement Report
INRIM Technical Report no. 46, January 2007.

In the Technical Report the work carried out at INRIM between December 2006 and January 2007 about the EUROMET Project 918 on the traceability of salinity measurements in seawater is reported. The project has been endorsed by the Electrochemistry Sub-Committee of EUROMET Technical Committee for Metrology in Chemistry. The Practical Salinity Scale PSS-78, endorsed by UNESCO/IAPSO, forms the basis of an internationally accepted method for calculating salinity from conductivity measurements. The practical salinity, S, of seawater is now defined in terms of the ratio of electrolytic conductivity of a seawater solution with that of a KCl solution with mass fraction of 32.4356 at the temperature of 15 ºC. For the Project 918 electrolytic conductivity measurements on standard seawater, IAPSO Standard Seawater (P-series) produced by OSIL, and on KCl solution produced by Merck have been carried out.

L. Busso, G. Crotti, G. Durin, M. Gandini, R. Garfagnini, P. Giudici
Characterisation of static and alternating low frequency magnetic fields generation systems for cellular studies
Rapporto Tecnico del Dip. di Fisica dell'Università di Torino, DFG Report - 04/2007.

Recently, the scientific literature reports on studies of the interaction of low frequency electromagnetic fields with some cellular transmembrane receptors, in particular amminoacids and Ca²⁺,K⁺, Mg⁺ ions in aqueous solution. Measuring the ionic current in a solution of glutammic-acid, a peak on the ionic current has been observed when the solution is exposed to a static magnetic field, in the range (1 to 100) nT, superimposed to a low frequency alternating magnetic field in the range (10 to 100) nT at the frequency of about (4 to 5) Hz. In this note we present the procedure adopted for the characterisation of the systems for the generation of the static and alternating magnetic fields. The accurate measurements of these fields is necessary for doing properly such type of experiment.

L. Callegaro
Josephson Array Waveform Synthesis at METAS: a guest researcher report
INRIM Technical Report no. 56, June 2007.

The report describes the work of a three-months period at METAS as guest researcher. The research topic is the development of a primary source of ac voltages, based on the Josephson effect. The work involved the setting up of the source, and measurements of the output waveforms. The source is based on a binary Josephson array developed at PTB, a driver electronics developed at NPL, and cryogenic and microwave apparatus present at METAS; it generates staircase approximation of sinewaves, with a sampling frequency up to 600 kHz and an output frequency up to a few kHz with 13-bit codes. Several preliminary experiments have been performed on the output waveform: measurement of the RMS value with a precision ac voltmeter, measurement of the output spectral properties, current buffering to drive multijunction thermal converters, and measurement of the amplitude of the fundamental harmonics with a sampling system which is also capable to drive a slave generator locking its amplitude to the Josephson waveform. The latter approach will provide a 24-bit low-distortion sinewave source, having current driving capabilities and directly traceable to the volt representation given by the Josephson effect.

F. Celegato, A. Magni
Sistema di Sputtering per la deposizione di film sottili
Rapporto Tecnico INRIM n. 74, novembre 2007.

Una nuova apparecchiatura per la produzione di film sottili, rivolta alla deposizione di film sottili magnetici, viene qui introdotta e descritta. Il sistema di sputtering si basa su processi di deposizione in DC e in RF, permettendo la produzione di film sottili/mulistrati di differenti materiali, sia conduttori che non conduttori, magnetici che non magnetici. I materiali prodotti e studiati possono essere di vario tipo, spaziando dai principali elementi ferromagnetici (Fe, Co, Ni), ai più comuni materiali conduttori usati per esempio per striplines (Rame), a materiali isolanti - usati per isolare elettricamente strati contigui (Al₂O₃, MgO). Inoltre, abbiamo prodotto target partendo da leghe e da nastri di importati materiali magnetici amorfi, come il Finemet and CoFeSiB. La qualità dei dispositivi che possiamo produrre è direttamente correlata alla pressione minima che si può ottenere nella macchina: potendo raggiungere 1^-7 mbar, riteniamo che film ultra-sottili di buona qualità possano essere prodotti con sufficiente affidabilità. Da queste premesse, crediamo che l'importanza di questo apparato sia fondamentale per il nostro gruppo, poiché ci permette di produrre internamente all'INRIM, film sottili e dispositivi di paricolare interesse per gli studi più recenti sui materiali magnetici.

N. De Leo, M. Fretto, V. Lacquaniti, F. Del piano
Sviluppo di dispositivi mixer SIS: fabbricazione, assemblaggio e prime caratterizzazioni a bassa temperatura
Rapporto Tecnico INRIM n. 57, ottobre 2007.

In questo rapporto tecnico vengono descritti i processi di fabbricazione e di assemblaggio di un dispositivo mixer a giunzione Josephson di tipo SIS (Superconduttore-Isolante-Superconduttore) realizzato presso l'INRIM. Vengono inoltre fornite le prime misure di caratterizzazione elettrica a bassa temperatura (4.2 K) eseguite in collaborazione con il Dipartimento di Astrofisica dell'Università di Milano (Prof. Sironi).

E. Ferrara
Applicazioni delle misure magnetiche per l'analisi e lo studio dei beni artistici e culturali
Rapporto Tecnico INRIM n. 77, dicembre 2007.

La conoscenza delle fenomenologie di comportamento dei materiali sotto l'azione di un campo magnetico è importante per numerose applicazioni nel campo dei beni culturali. La maggior parte delle sostanze magnetiche è costituita da composti del ferro, fra i più comuni costituenti della crosta terrestre, utilizzati storicamente come risorsa materiale, per esempio per opere di muratura, per la realizzazione di manufatti ceramici o per la preparazione di pigmenti. Nei materiali, dimensioni, distribuzione e orientazione delle particelle ferromagnetiche dipendono dalla composizione, dalla tecnologia di produzione e dalle caratteristiche del campo terrestre esistente al momento della produzione. In particolare, la configurazione magnetica di un prodotto costituisce una sorta di registrazione naturale delle condizioni ambientali originarie e della loro evoluzione nel tempo. Oltre a costituire un peculiare strumento di investigazione delle tecnologie di produzione di manufatti di interesse storico, artistico e culturale, lo studio delle proprietà magnetiche rimanenti nei materiali (argille, terrecotte, pigmenti, malte, suoli) confrontate con la variazione secolare del campo terrestre, può permetterne una datazione indipendente.

U. Pogliano, G. C. Bosco, M. Lanzillotti
Metodi di caratterizzazione di misuratori per valori di tensioni alternate inferiori a 200 mV nel campo di frequenza da 1 kHz a 1 MHz
Rapporto Tecnico INRIM n. 61, luglio 2007.

Il rapporto tecnico mette a confronto i risultati ottenuti nella taratura di misuratori di tensione alternata nel campo di valori da 1 mV a 200 mV e per frequenze da 1 kHz a 1 MHz. I metodi di misura utilizzati prevedono l'impiego di un calibratore Fluke 5700A come sorgente di tensione, di un trasferitore multiportata Fluke mod. 792A, di due divisori resistivi in rapporto 1:10 e 1:100 e di un trasformatore a doppio stadio con rapporti 1:10 e 1:100, progettato e realizzato presso l'INRIM. Vengono riportati i risultati ottenuti dalla taratura, con il metodo di step-down, dei divisori resistivi e dei due rapporti del trasformatore a doppio stadio. Sono poi riportati e analizzati i risultati ottenuti, dal successivo utilizzo dei divisori resistivi e del trasformatore a doppio stadio caratterizzati, nella taratura del trasferitore Fluke mod. 792A e del misuratore di alternata Fluke 5790A.

M. Sellone, A. Capelli
Design, realization and characterization of a specific T-junction in 7 mm coaxial line for AC-DC Transfer Difference measurements
INRIM Technical Report no. 81, December 2007.

In this technical report we will describe the realization and characterization of a Tee designed in order to be used in AC-DC Transfer Difference measurements. This Tee has been designed specifically for the Calorimetric Thermal Voltage Converter that will extend the metrological capabilities in the power measurements field at low frequencies.

M. Sellone, A. Capelli
Progetto e realizzazione di un Thermal Voltage Converter Calorimetrico per frequenze fino a 1 GHz
Rapporto Tecnico INRIM n. 50, aprile 2007.

In questo rapporto tecnico vengono descritte le fasi di progetto e realizzazione di un nuovo Thermal Voltage Converter di tipo Calorimetrico da utilizzare nel laboratorio di Alta Frequenza dell'INRiM per estendere le capacità metrologiche nel campo delle misure di potenza. Infatti la tecnica microcalorimetrica usata attualmente risulta limitata inferiormente alla frequenza di 10 MHz, al di sotto della quale il rumore non permette di distinguere il segnale da rivelare. Mediante l'utilizzo di un CTVC sarà possibile effettuare le misure di potenza attraverso una misura di tensione RF con valori di potenza in ingresso più alti che consentiranno di ottenere segnali di uscita maggiormente distinguibili dal rumore di fondo.

M. Sellone, L. Brunetti
Procedure di misura ad una porta per dispositivi a due porte che presentano differenti connettori
Rapporto Tecnico INRIM n. 82, dicembre 2007.

I dispositivi a due porte per alta frequenza sono generalmente caratterizzati attraverso misure eseguite con Analizzatori di Reti Vettoriali. Ci sono, però alcuni tipi di dispositivi che non possono essere misurati in questo modo, poichè presentano due differenti connettori che non possono pertanto essere direttamente connessi alle porte dello strumento. In questo rapporto tecnico sono descritti delle tecniche alternative di misura che possono essere utilizzate per caratterizzare un dispositivo a due porte tramite misure ad una porta sola. Al termine viene anche presentato un esempio numerico legato alla caratterizzazione di una specifica linea coassiale che presenta due differenti connettori.