International and National Journals

G. Bertotti, I. D. Mayergoyz (Editors)
The science of hysteresis. 3 volumes, Elsevier

VOLUME I - Mathematical Modeling and Applications

• A. Visintin: Mathematical models of hysteresis
• M. Brokate, A. V. Pokrovskii, D. Rachinskii, O. Rasskazov: Differential equations with hysteresis via a canonical example
• I. D. Mayergoyz: Scalar Preisach models of hysteresis
• I. D. Mayergoyz: Vector Preisach models of hysteresis
• I. D. Mayergoyz: Stochastic aspects of hysteresis
• S. A. Belbas: Control of systems with hysteresis
• C. Korman: Binary detection and rectangular hysteresis operators
• R. Cross, J. Darby, L. Piscitelli: Hysteresis and unemployment: a preliminare investigation

VOLUME II - Physical Modeling, Micromagnetics, and Magnetization Dynamics

• G. Bertotti, V. Basso, M. LoBue, A. Magni: Thermodynamics, hysteresis, and thermal relaxation, pp. 1-106
• J. P. Sethna, K. A. Dahmen, O. Perkovic: Random-field Ising models of hysteresis
• G. Durin, S. Zapperi: The Barkhausen effect, pp. 181-267
• DeSimone, R. V. Kohn, S. Muller, F. Otto: Recent analytical developments in micromagnetics
• R. Dittrich, T. Schrefl, J. Fidler, D. Suess, W. Scholtz, H. Fortster: Computational aspects of micromagnetics
• G. Bertotti, I. D. Mayergoyz, C. Serpico: Nonlinear magnetization dynamics. Switching and relaxation phenomena, pp. 435-565
• G. Bertotti, I. D. Mayergoyz, C Serpico: Non linear magnetization dynamics. Magnetization modes and spin waves under rotating fields. pp. 567-642

VOLUME III - Hysteresis in Materials

• F. Fiorillo, C. Appino, M. Pasquale: Hysteresis in magnetic materials, pp. 1-190
• Beatrice, P. Tiberto: Magnetic Hysteresis in nanostructured materials, pp. 191-255
• D. Mayergoyz: Superconducting hysteresis
• Damjanovic: Hysteresis in piezoelectric and ferroelectric materials
• J. Ortin, A. Planes, L Delaey: Hysteresis in shape-memory materials
• R. A. Guyer: Hysteretic Elastic systems; geophysical mat
• D. Flynn, H. McNamara, P. O'Kane, A. Pokrovskii: Application of the Preisach model in soil-moisture hysteresis

J. Degauque, F. Fiorillo
Alliages magnétiques doux enrichis en silicium
"Matériaux magnétiques en génie électrique 1"(Traité EGE, série Génie électrique), chapitre 4, pp. 227-292, Kedous-Lebouc Afef, Hermes - Lavoisier 2006.

The structural, magnetic, and mechanical properties of the Fe-Si ferromagnetic alloys having Si concentrations exceeding the conventional range found in the commercial low-carbon steels and the grain-oriented and non-oriented laminations are comprehensively discussed. The superior magnetic performances of these high-Si alloys are illustrated in the light of the physical theories of magnetization process and losses, while the mechanisms responsible for their inferior mechanical behavior are identified and thoroughly assessed. The preparation methods, ranging from the rapid solidification process to the Si-enrichment of conventional laminations by the Chemical Vapour Deposition method are also presented. It is stressed that highly energy efficient applications of these materials are already available and future developments towards their use in a multitude of superior electrical and electronic apparatus can be envisaged.

P. Allia, M. Coisson, F. Spizzo, P. Tiberto, F. Vinai
Magnetic correlation states in cosputtered granular Ag_100-xFe_x films
Physical Review B, Vol. 73, p. 054409, 2006.

Measurements of isothermal magnetization, initial and high-field static susceptibility, and magnetoresistance have been performed at various temperatures on five Ag_100-xFe_xgranular films of variable Fe content (10 <×<30) obtained by co-sputtering. Magnetoresistance and magnetization data have been systematically combined to determine the magnetic correlation volume in each sample and its evolution with temperature and magnetic field. A coherent picture of the whole set of Ag_100-xFe_xfilms has been obtained. On increasing x, these alloys exhibit a magnetic behavior of increasing complexity, from the interacting superparamagnetic phase with weakly interacting magnetic moments and small correlation volumes, to frustrated ferromagnetism with strong magnetic interactions, loss of physical identity of Fe particles, extended correlation volumes. The degree of alignment of individual magnetic moments within a correlation volume, and the stability of correlation volumes themselves against an external magnetic field are discussed in some detail.

V. Basso, M. LoBue, C. P. Sasso, G. Bertotti
Thermodynamic aspects of magnetic-field-driven phase transformations in Gd-Si-Ge alloys
Journal of Applied Physics, Vol. 99, p. 08K907, 2006.

A temperature-dependent Preisach model is proposed to describe hysteresis in materials in which a structural phase transformation driven by the magnetic field takes place. The model is applied to the interpretation of the temperature dependence of hysteretic magnetization curves measured for Gd-Si-Ge alloys. Predictions about the entropy exchanged during transformations under increasing or decreasing field reveal the role played by internal dissipative processes.

G. Bertotti, I. D. Mayergoyz, C. Serpico
Analysis of random Landau-Lifshitz dynamics by using stochastic processes on graphs
Journal of Applied Physics, Vol. 99, p. 08F301, 2006.

A randomly perturbed Landau-Lifshitz-Slonczewski equation is transformed into a stochastic differential equation for free energy. The stochastic differential equation is defined in graphs that reflect the energy landscape of magnetic system. The stochastic differential equation for energy contains additional thermally generated drift terms that may appreciably affect slow time-scale magnetization dynamics. The effect of these thermal drift terms on energy distribution near equilibria and limit cycles (self-oscillations) is discussed.

R. Bonin, G. Bertotti, I. D. Mayergoyz, C. Serpico
Spin-torque-driven magnetization dynamics in nanomagnets subject to magnetic fields perpendicular to the sample plane
Journal of Applied Physics, Vol. 99, p. 08G508, 2006.

We analytically solve the Landau-Lifshitz-Gilbert equation with the addition of the spin-torque term proposed by Slonczewski [J. Magn. Magn. Mater. 159, L1 (1996)] for the case of external magnetic field perpendicular to the sample plane. By using methods of nonlinear dynamical system theory we construct the complete stability diagram of the spin-torque-driven dynamics in the field-current control plane. Our predictions are compared with recent experimental results.

C. Serpico, G. Bertotti, I. D. Mayergoyz, M. d'Aquino, R. Bonin
Thermal stability in spin-torque-driven magnetization dynamics
Journal of Applied Physics, Vol. 99, p. 08G505, 2006.

In this article, thermal fluctuations in spin-torque-driven magnetization dynamics are described phenomenologically by introducing a Gaussian white noise term in the Landau-Lifshitz-Slonczewski equation. The ensuing stochastic magnetization dynamics is studied by considering the Fokker-Planck equation for the probability distribution of magnetization. The corresponding Fokker-Planck for the energy probability distribution is then derived in the limit of small fluctuations by averaging with respect to fast-time-scale precessional dynamics. By using this equation the stationary probability distribution of energy is analytically determined. This distribution has peaks around stable stationary states as well as around self-oscillatory regimes. On this basis, we define an effective potential barrier controlling switching between stable equilibrium states and self-oscillatory regimes.

M. Dimian, I. D. Mayergoyz, G. Bertotti, C. Serpico
Multiscale analysis of magnetization dynamics driven by external fields
Journal of Applied Physics, Vol. 99, p. 08G104, 2006.

The multiscale approach to the magnetization dynamics driven by external magnetic fields is presented. In this approach, the Landau-Lifshitz equations are represented in an equivalent form, where the magnetic free energy is used as one of the state variables. This form clearly separates fast and slow dynamics and, consequently, it can be used for the development of perturbation and multiple scale techniques. Several applications of this approach to the precessional magnetization switching are discussed.

M. d'Aquino, C. Serpico, G. Coppola, I. D. Mayergoyz, G. Bertotti
Midpoint numerical technique for stochastic Landau-Lifshitz-Gilbert dynamics
Journal of Applied Physics, Vol. 99, p. 08B905, 2006.

The implicit midpoint time-integration technique is applied to the stochastic Landau-Lifshitz-Gilbert (LLG) equation. The numerical scheme converges to the Stratonovich solution in the limit of vanishing time step. It preserves the magnetization magnitude and the main energy balance properties of the LLG equation independently of the time step. The numerical technique is then applied to the study of superparamagnetic state in a small spheroidal particle, and the numerical results are compared with the theory.

S. Flohrer, R. Schäfer, J. McCord, S. Roth, L. Schultz, F. Fiorillo, G. Herzer
Dynamic magnetization process of nanocrystalline tape wound cores with transverse field-induced anisotropy
Acta Materialia, Vol. 54, no. 18, pp. 4693-4698, 2006.

The correlation between dynamic magnetic domain formation and dynamic magnetization loss is studied in nanocrystalline FeCuNbSiB tape wound cores with different strengths of transverse field-induced anisotropy. A significant excess loss component is measured, in particular for high induction levels. The excess loss cannot be explained by homogeneous magnetization rotation, the ideal magnetization process for a transverse field-induced anisotropy. In fact, dynamic domain observation reveals inhomogeneous rotation of magnetization, wall displacement processes, and domain nucleation besides homogeneous rotation. Domain refinement is accordingly observed with increasing frequency. The domain width is smallest for cores with weak induced anisotropy, where excess loss is the lowest. In these cores, surface roughness yields residual domains, which persist at field strengths above the inductively measured saturation field.

C. Beatrice, O. Bottauscio, M. Chiampi, F. Fiorillo, A. Manzin
Magnetic loss analysis in Mn-Zn ferrite cores
Journal of Magnetism and Magnetic Materials, Vol. 304, no. 2, pp. e743-e745, 2006.

Magnetic losses have been measured and analyzed upon a wide range of frequencies in Mn-Zn ferrite ring cores. Exploiting the concept of loss separation and modeling the conductivity process in the heterogeneous material as a function of frequency, the role of the different energy dissipation mechanisms has been elucidated. It is shown, in particular, that eddy current effects can be appreciated, in standard materials and cores, only on approaching and overcoming the MHz range. The basic mechanism for hysteresis and low-frequency losses is therefore identified with the domain wall relaxation engendered by spin damping processes. Resonant absorption of energy associated with magnetization rotation is in turn deemed to chiefly contribute to the loss upon the practical range of frequencies going from a few 10⁴ Hz to a few MHz.

F. Vinai, M. Coïsson, P. Tiberto
High-frequency magneto-impedance in metastable metallic materials: an overview
Journal of Magnetism and Magnetic Materials, Vol. 300, no. 1, pp. e82-e87, 2006.

The giant magneto-impedance effect (GMI) is a common feature of a wide class of metastable ferromagnetic alloys. This effect can be enhanced by submitting the as-prepared materials to suitable thermal treatments. Recently, a remarkably high magneto-impedance response has been observed in the GHz region for several systems. The increase in miniaturization of telecommunication devices dramatically increases the working frequencies; as a consequence, the interest in studying magneto-impedance effect leads to microwave region. In this paper, analogies and differences among the magneto-transport effect observed in ferromagnetic metastable alloys will be highlighted and discussed from the experimental point of view in a wide range of frequencies.

F. Fiorillo, G. F. Durin
A reference system for the measurement of low-strength magnetic flux density
Journal of Magnetism and Magnetic Materials, Vol. 304, no. 2, pp. e540-e542, 2006.

Magnetic flux density standards traceable to the SI units have been developed at IEN-INRIM, by which dissemination for general measurement and testing activities can be pursued. The reference system covers a range of values extending from to µ₀H ~ 1 T and µ₀H ~ 10 µT is centered on the use of NMR magnetometers, calibrated coils, and stable current sources. The relative measuring uncertainty of the system is shown to increases with decreasing the field strength value and it is estimated to range between a few 10^-6 and some 10^-3.

O. Bretcanu, E. Verné, M. Cöisson, P. Tiberto, P. Allia
Temperature effect on the magnetic properties of the coprecipitation derived ferrimagnetic glass-ceramics
Journal of Magnetism and Magnetic Materials, Vol. 300, no. 2, pp. 412-417, 2006.

Ferrimagnetic glass-ceramic materials are promising candidates for destruction of cancerous cells by hysteresis loss, as a consequence of the increase of the local temperature when an alternating magnetic field is applied. The glass-ceramics prepared in this work contain magnetite and hematite crystals in a glassy matrix. They can be prepared by melting the coprecipitation-derived precursors at temperatures higher than 1400 ºC. The influence of the melting temperature on the magnetic properties of these glass-ceramics has been analysed. Room temperature hysteresis cycles in quasi-static conditions were performed using two different magnetic field, one of 12 kOe, and the other one of 500 Oe. The heat generation was estimated from calorimetric measurements, using a magnetic induction furnace. The magnetic hysteresis parameters are strongly affected by the glass-ceramics microstructure, which is influenced by the melting temperature.

O. Bretcanu, E. Verné, M. Cöisson, P. Tiberto, P. Allia
Magnetic properties of the ferrimagnetic glass-ceramics for hyperthermia
Journal of Magnetism and Magnetic Materials, Vol. 305, no. 2, pp. 529-533, 2006.

Magnetic materials play a key-role in magnetic induction hyperthermia for the treatment of cancer. In this paper, we analyse the magnetic properties of ferrimagnetic glass-ceramics with the composition in the system SiO₂-Na₂O-CaO-P₂O₅-FeO-Fe₂O₃, as a function of the melting temperature. These materials were obtained by melting of commercial reagents in the temperature range of 1400-1550 ºC. Room-temperature magnetic measurements were performed by means of a vibrating sample magnetometer at room temperature. The power loss was determined from calorimetric measurements, using a magnetic induction furnace. The highest power loss (61 W/g) has been obtained for samples melted at 1500 ºC. The heat generation of the ferrimagnetic glass-ceramics prepared by two different synthesis methods (traditional melting and coprecipitation-derived) will be compared. These materials are expected to be useful in the localised treatment of cancer.

C. Ragusa, F. Fiorillo
A three-phase single sheet tester with digital control of flux loci based on the contraction mapping principle
Journal of Magnetism and Magnetic Materials, Vol. 304, no. 2, pp. e568-e570, 2006.

Tight control of flux loci in 2D testing of soft magnetic laminations is realized by a method based on the principle of contraction mapping. It is implemented through digital control of the currents supplying a three-phase yoke magnetizer and the use of circular samples. Faithful realization of the prescribed loci and good measuring accuracy are demonstrated in grain-oriented and non-oriented Fe-Si laminations.

F. Fiorillo
Anisotropy and magnetization process in soft magnets: Principles, experiments, applications
Journal of Magnetism and Magnetic Materials, Vol. 304, no. 2, pp. 139-144, 2006.

Understanding and controlling the anisotropy energy and its effects has proved vital to the development of soft magnetic materials and their applications. Indeed, acting on composition and structure and working out specific annealing treatments, a large variety of anisotropy-governed behaviors under DC and AC excitation can be obtained. These are discussed in the present paper, together with special problems arising in the characterization of anisotropic soft magnets and a few significant applications. It is stressed how features like J-H loop shape, energy losses, and magnetoresistance effects can be controlled, in crystalline and amorphous materials, by the methods of induced anisotropy. The high-frequency behavior of these materials can be strongly affected by the anisotropy field via resonant absorption of energy. This calls for tradeoff between the values of permeability and resonance frequency.

C. P. Sasso, V. Basso, M. LoBue, G. Bertotti
Carnot cycle for magnetic materials: The role of hysteresis
Physica B: Physics of Condensed Matter, Vol. 372, no. 1-2, pp. 9-12, 2006.

The role of hysteresis in a refrigeration thermodynamic cycle involving ferromagnetic materials is discussed. A model allowing to calculate magnetization, entropy and entropy production in systems with hysteresis is used to compute a non-ideal Carnot cycle performed on a ferromagnetic material.

V. Basso, A. Magni, G. Bertotti
First steps towards a state classification in the random-field Ising model
Physica B: Physics of Condensed Matter, Vol. 372, no. 1-2, pp. 243-246, 2006.

The properties of locally stable states of the random-field Ising model are studied. A map is defined for the dynamics driven by the field starting from a locally stable state. The fixed points of the map are connected with the limit hysteresis loops that appear in the classification of the states.

L. Santi, F. Bohn, A. D. C. Viegas, G. Durin, A. Magni, R. Bonin, S. Zapperi, R. L. Sommer
Effects of thickness on the statistical properties of the Barkhausen noise in amorphous films
Physica B: Physics of Condensed Matter, Vol. 384, no. 1-2, pp. 144-146, 2006.

The statistical properties of the Barkhausen noise (BN) in thin amorphous films are studied as a function of both the nominal composition and the thickness. BN was observed in single films with nominal compositions Fe_73.5Cu₁Nb₃Si_22.5-xB_x (with x=4 and 9) in the thickness range 20 nm-5 µm. The distributions of Barkhausen jump sizes and duration times were obtained and fitted to power laws with critical exponents T=1.25±0.05 and α=1.60±0.05, respectively.

C. Appino, M. Coïsson
Reversible and irreversible magnetization processes in materials displaying two-dimensional hysteresis
Physica B: Physics of Condensed Matter, Vol. 372, no. 1-2, pp. 133-137, 2006.

We have investigated the vector hysteresis properties of Co-based disk-shaped amorphous specimens, with in-plane macroscopic uniaxial anisotropy. The samples were subjected to a field H_a applied in the sample plane along a direction making with the easy axis an angle θ_Ha ranging between 0º and 90º. The role played by reversible and irreversible magnetization processes is studied along the first magnetization curve and the major loop. We have identified the parameters of a vector model based on the Stoner-Wohlfarth approach, and accounting for spin rotations and domain wall assisted processes. Finally, we have demonstrated the possibility of reproducing the whole vector hysteresis behavior from the measurement of the hysteresis loops for θ_Ha=0º and 90º.

C. P. Sasso, M. Pasquale, L. Giudici, S. H. Lim, S. M. Na
Piezomagnetic coefficients of polymer bonded Co-ferrites
Sensors & Actuators: A. Physical, Vol. 129, no. 1-2, pp. 159-162, 2006.

Experimental results concerning the scalar piezomagnetic coefficients of Co-based ferrites at room temperature are presented and discussed. To increase the mechanical properties, the ferrite powders are bonded by a phenol-based matrix. The Young's modulus of the samples is about 8 GPa. The permeability of the samples µ_z^σ(H) and the slope of magnetostriction curve d₃₃^σ(H) at constant stress, which are the most important piezomagnetic coefficients for stress sensing and mechanical actuation, are discussed in detail with respect to sample density changes due to different content of binder and compaction pressure.

C. Serpico, R. Bonin, G. Bertotti, I. D. Mayergoyz, M. d'Aquino
Thermal stability in uniaxial nanomagnets driven by spin-polarized currents
IEEE Transactions on Magnetics, Vol. 42, no. 10, pp. 2679-2681, 2006.

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. It is shown that the deterministic dynamics and the thermal relaxation are both governed by an effective potential including the effect of current injection.

C. Beatrice, F. Fiorillo
Measurement and prediction of magnetic losses in Mn-Zn ferrites from DC to the megahertz range
IEEE Transactions on Magnetics, Vol. 42, no. 10, pp. 2867-2869, 2006.

The magnetic energy losses and their frequency dependence in Mn-Zn ferrites have been investigated in theory and experiment. A novel theoretical approach has been developed, which is based on the concept of loss decomposition and the appraisal of the separate contributions provided by domain wall displacements and moment rotations. It is shown that the role of eddy currents in energy dissipation is a minor one and can be appreciated in the megahertz region only. The loss contribution by domain walls versus frequency is obtained from knowledge of the quasistatic energy loss, whereas the rotational real and imaginary permeabilities are derived as solutions of the Landau-Lifshitz-Gilbert equation for distributed values of the effective anisotropy field. The model successfully applies to results obtained on commercial ferrite ring samples.

G. Durin, S. Zapperi
The role of stationarity in magnetic crackling noise
Journal of Statistical Mechanics: Theory and Experiment, PO1002, 2006.

We discuss the effect of the stationarity on the avalanche statistics of Barkhausen noise signals. We perform experimental measurements on an Fe₈₅B₁₅ amorphous ribbon and compare the avalanche distributions measured around the coercive field, where the signal is stationary, with those sampled through the entire hysteresis loop. In the first case, we recover scaling exponents (τ~1.38, α~1.65) close to the commonly observed values for other amorphous materials, while in the second the exponents are significantly larger (τ~1.7, α~2.2). We provide a quantitative explanation of the experimental results through a model for the depinning of a ferromagnetic domain wall. The present analysis sheds light on the unusually high values for the Barkhausen noise exponents measured by Spasojevic et al. [Phys. Rev. E 54 2531 (1996)].

M. Pasquale, F. Celegato, M. Coïsson, A. Magni, S. Perero, P. Kabos, V. Teppati, S. Han, J. Kim, S. H. Lim
Structure, ferromagnetic resonance and permeability of nanogranular CoFeBNi films
Journal of Applied Physics, Vol. 99, p. 08M303, 2006.

The static and microwave magnetic properties of soft nanogranular (Fe_0.7Co_0.3)₇₁B₂₂Ni films with a 2 T saturation magnetization are presented as functions of thickness, ranging from 136 to 235 nm. Microwave permeability values from 60 to 260 are measured and ferromagnetic resonance frequencies up to 6.8 GHz are found using a vector network analyzer, connected to coplanar/microstrip structures loaded with the ferromagnetic films. Topographic and magnetic structures down to 20-40 nm were observed by atomic/magnetic force microscopy. The combination of reasonable values of the permeability and high ferromagnetic resonance frequency makes these nanogranular materials useful in the development of inductive microwave components.

C. P. Sasso, M. Pasquale, L. Giudici, S. Besseghini, E. Villa, L. H. Lewis, T. A. Lograsso, D. Schlagel
Magneto-structural transition and adiabatic temperature variation in poly- and single-crystal Ni₂MnGa alloys
Journal of Applied Physics, Vol. 99, p. 08K905, 2006.

The magnetocaloric response of off-stoichiometric Ni₂MnGa polycrystal and single-crystal samples with a Curie temperature coincident with the martensitic transition temperature was investigated. The direct measurement of temperature change (ΔT_ad) during an adiabatic transformation under a maximum field variation H=5.6×10⁶ A/m (7 T) was performed. The polycrystalline sample shows a maximum ΔT_ad ≈ 1.5 K at a temperature close to the structural transition. The value of ΔT_ad and the 20 K span of the ΔT_ad peak encourage further studies of the effect of microstructure on the magnetocaloric response.

V. Basso, C.P. Sasso, M. Lo Bue, G. Bertotti
Effect of material hysteresis in magnetic refrigeration cycyles
International Journal of Refrigeration, Vol. 29, pp. 1358-1365, 2006 (Special Issue: Magnetic Refrigeration at Room Temperature, H. Auracher and P.Egolf editors).

In this paper we make use of the concepts of out-of-equilibrium thermodynamics applied to systems with hysteresis in order to model the magnetic material employed as a working substance in magnetic refrigeration cycles. The approach developed leads to a detailed description of heat fluxes as well as the entropy production connected with hysteresis. As an example we discuss Carnot and AMR refrigeration cycles where hysteresis effects are included.

M. d'Aquino, G. Bertotti, C. Serpico, I. D. Mayergoyz, R. Bonin
Foldover, quasiperiodicity, and spin-wave instabilities in ultra-thin magnetic films
IEEE Transactions on Magnetics, Vol. 42, pp. 3195-3197, 2006.

We study magnetization dynamics in a uniaxial ultra-thin ferromagnetic disk subject to spatially uniform microwave external fields. As a consequence of the rotational invariance of the system, 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.

M. Pasquale, S. Perero, G. Bertotti, P. Kabos, S. H. Lim
Microwave resonances in nanogranular (Fe_0.7Co_0.3)₇₁B₂₂Ni₇ films
IEEE Transactions on Magnetics, Vol. 42, pp. 3054-3056, 2006.

We have analyzed the microwave behavior of soft nanogranular (Fe_0.7Co_0.3)₇₁B₂₂Ni₇ films which present a dc permeability from 60 to 280, a resistivity of 8 to 9 ×10^-7Omega m and a zero-field double ferromagnetic resonance peak at frequencies ranging from 3.8 to 8.35 GHz. The high frequency and large line-width of the observed resonances allows for possible applications in microwave absorbers in a frequency range extending from 6 to 10 GHz.

C. Beatrice, M. Coisson, E. Ferrara, E. Olivetti
Relevance of magnetic properties for the characterization of burnt clkays and archaeological tiles
Physics and Chemistry of the Earth, Special Issue on Archaeomagnetic Applications for the Rescue of Cultural Heritage.

The measurement of hysteresis loops has been applied and combined with colour survey to characterise the magnetic properties of burnt clays and archaeological tiles. Calcareous and non-calcareous clays, along with tile fragments excavated from the sites of the ancient Roman towns of Pompei and Gravina di Puglia, in Southern Italy, are examined. The ferrimagnetic character of the clays, in general, enhances with increasing firing temperatures until vitrification processes occur (900 - 1000 ºC) dissolving iron oxides and dispersing the colour and magnetic properties they provide. High values of saturation magnetization are observed in clays with relevant calcareous content after firing above 900 ºC, which results in the formation of Ca-silicates able to delay the onset of the vitrification processes. Enhanced ferrimagnetic character, mostly depending on the growth in number and volume of iron oxide particles, is associated with the development of an intense reddish hue.

F. Fiorillo, C. Beatrice, O. Bottauscio, A. Manzin, M. Chiampi
An approach to magnetic losses and their frequency dependence in Mn-Zn ferrites
Applied Physics Letters, Vol. 89, pp. 122513-1/3, 2006.

The frequency dependence of the magnetic energy losses in sintered Mn-Zn ferrites is predicted from the quasistatic regime to the megahertz range. The predicting model is based on the appraisal of the contributions by domain wall (dw) displacements and magnetization rotations and the related relaxation-resonant-type dissipation mechanisms. Eddy currents are demonstrated to play little to negligible role. The frequency dependence of the dw generated losses is calculated from knowledge of the quasistatic losses, whereas the contribution by rotations is obtained via the Landau-Lifshitz-Gilbert equation, assuming distributed anisotropy fields. The model excellently applies to the frequency response of commercial ferrites.

Technical Reports

F. Cabiati, F. Fiorillo
Proposta per una procedura di autovalutazione in un Ente di Ricerca
Rapporto Tecnico INRIM n. 13, maggio 2006.

A self-evaluation procedure is here proposed, which is deemed to apply to a research institution whose different activities are carried out in accordance with specifically defined aims. The qualification of these activities is assumed to require an evaluation of the obtained results based on their coherence with established goals, besides universally acknowledged values. The devised procedure aims, in particular, at producing indexes, through a quantitative and qualitative appraisal of the whole activity. This implies in practice that specific categories for the performed activities are recognized and objective criteria and elements for the qualification of the obtained results are identified. With reference to a research institution in Metrology, an ensemble of categories of activity, globally defining the operating framework of this institution, have been identified. Each category of activity has been associated with a number of categories of achievement, these ones being selected from a suitable collection, which is pre-defined on the basis of relevance criteria. In order to objectively evaluate the importance of the achievements, suitable indicators are introduced and a value is assigned to each of them, under a scheme based on the definition of criteria of quality. At the end, an evaluation matrix can be laid down, where each numerical figure is subjected to a suitable normalization procedure, in order to place the different categories of activity on equal footing. The judgment procedure basically consists in providing figures for the different indicators, according to the pre-determined quality criteria and through the use of the evaluation matrices, an example of which, pro forma compiled, is provided.

P. Fisicaro, A. Adriaens, E. Ferrara, E. Prenesti
Amperometric determination of dissolved oxygen
INRIM Technical Report no. 44, December 2006.

This technical report illustrates the results obtained in the development of an electrochemical apparatus for the determination of the amount of dissolved oxygen in aqueous solutions. The project is conducted in cooperation with the Analytical Department of the University of Gent and the Analytical Department of the University of Torino. The measurement system consists in an amperometric cell designed on the model of Clark-type sensors and represents the first attempt at the development of a potential primary standard. The paper describes in detail the principles of the analytical technique as well as the procedure for the setting-up and the calibration of the cell. A preliminary discussion of the main contributions to the overall measurement uncertainty is also reported.