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Il Tempo della Scienza

Seminari tecnici 2015

Sala Conferenze (Edificio M)
Strada delle Cacce 91, Torino

Data Relatore Titolo
26 febbraio
ore 15
Ed. D
Paolo Bortolotti
Unité Mixte de Physique CNRS/Thales, Palaiseau, France
Novel paths for rf applications based on spintronics

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Spintronics consists on manipulating magnetic electronic spins rather than, or in addition to, charges through electrical currents and/or magnetic fields. This technology has revolutionized the market of read-head applications and other types of magnetic sensors. Recently, a lot of promising studies have been done for active elements such as memories (see for example the recent developments on perpendicular STT-MRAM), spin transistors and more generally logic spin gates; however, those functionalities are far from being implemented into real devices. Nevertheless, we believe that concerning radio-frequency (rf) applications, spintronics is now mature enough for proposing interesting and industrially attractive active functionalities and foster the development of a new generation of rf devices such as filters, frequency detectors, synthesizers, etc=85 In this seminar I will present some of the recent works of our laboratory on the subject.
The main brick for this new generation of rf applications [1] is the spin-transfer nano oscillator (STNO), which is a magnetic tunnel junction (MTJ) controlled by a dc current. In particular, we are focusing on vortex-based STNOs, consisting of an MTJ where the free layer is in the magnetic vortex configuration, separated from a synthetic anti-ferromagnetic polarizer layer by an MgO barrier. The vortex consists of a circular in-plane magnetization with a central out-of-plane core, which can be excited by a dc current, Idc, resulting in a steady gyrotropic motion of the vortex core [2]. This motion is transformed into an rf signal in the MHz/GHz range, through the tunnel magnetoresistance (TMR) effect. A phase-locked loop (PLL) implementation can be used to further improve the characteristics of such oscillator. Our latest achievements make us confident that a synthesizer based on vortex STNOs will be good enough for device operations.
Furthermore, the vortex core can be resonantly excited by an rf current, Irf, if the frequency of the current matches the frequency of the gyrotropic mode [3], which is the main ingredient for a spintronic frequency detector. In this context, I will briefly present a new type of STNO frequency detector based on vortex core expulsion, displaying promising features which can potentially constitute the basis of a new generation of rf applications.
I will also present some novel ideas on STNO-based associative memories [4]: by mimicking the behavior of our brain, we will consider an array of STNOs and take advantage of their mutual synchronization to perform associative memory functionalities.
Another interesting use of spintronics for rf application resides in the field of magnonics, i.e., the use of spin waves excitations (magnons) for information treatment. I will show that the information can be encoded in the phase of the magnetostatic spin wave and easily manipulated; miniaturized and low energy consumption devices for both logic [5] and rf functionalities, e.g., a magnonic filter, can be indeed conceived.
I acknowledge financial support from ANR agency (SPINNOVA ANR-11-NANO-0016; MEMOS ANR-14-CE26-0021-03; NANOSWITI ANR-11-BS10-003-05) and EU FP7 grant (MOSAIC No. ICT-FP7-n317950).

1. Building blocks: N. Locatelli et al., Nature Mater. 13, 11 (2014)
2. Vortex STNO: A. Dussaux et al., Nature Commun. 1, 8 (2010)
3. Detection: A. S. Jenkins et al., Appl. Phys. Lett. 105, 17 (2014)
4. Associative memories: MEMOS ANR-14-CE26-0021-03
5. Magnonics: Chumak et al., Nat. Commun. 5, 4700 (2014) & ref. therein
19 febbraio
ore 14:30
Ed. D
Mikhail Aleksandrovich Malygin
Head of the Department of Industrial Metrology
D.I. Mendeleyev Institute for Metrology (VNIIM), Russia
Laboratory of Metrology of magnetic measurements and nondestructive testing at UNIIM

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The talk aims to present our lab, our achievements and perspectives for possible further collaboration and finally to get some experience exchange. The presentation will briefly introduce metrological system of Russia, distribution of centres and institutes in the country. After that location and significance of UNIIM and presented laboratory will be determined, and then presentation will focus on the list of measurement capabilities and activities that our laboratory is specialized on, adding some general information.
19 febbraio
ore 11
Gaetano Scamarcio
Università degli Studi di Bari "Aldo Moro", Politecnico di Bari
Dipartimento Interateneo di Fisica "M. Merlin"
CNR - Istituto di Fotonica e Nanotecnologie
Trace gas sensing and imaging with terahertz quantum cascade lasers

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A wide variety of application areas are eagerly aiming at the development of novel sensing and imaging systems exploiting the availability of quantum cascade laser (QCL) compact semiconductor sources emitting in the mid-infrared and terahertz ranges. After reviewing the state-of-the-art in this fast growing field, I will present our recent demonstration of quartz-enhanced photo-acoustic trace gas sensors based on THz QCLs. Also, I will illustrate our theoretical and experimental results on the coherent multimode dynamics of QCLs and their intrinsic stability under strong optical feedback, showing examples of exploitations in the field of self-mixing interferometry and the development of a novel detectorless contact-free imaging method to monitor the free electron density in semiconductor structures.
12 febbraio
ore 11
Ruggero Vaglio
Dipartimento di Fisica, Università di Napoli Federico II
Role of thermal boundary resistance effects in superconducting cavities for particle accelerators

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New generation of accelerators require increasing superconducting cavity performances. Kapitza thermal resistance and, more in general, thermal boundary resistance effects have been often considered as a possible source of "non-ideal" cavity behavior, through the formation of a temperature difference between the inner cavity superconducting surface and the helium bath. However the general assessment reported in the literature is that such effects can be generally neglected, at least at low or moderate input power.
Here we present new data on small test 6Ghz cavities, showing new evidence of the relevance of thermal effects.
Routes for lowering the Kapitza resistance and to improve the overall cavity performances are finally discussed.
5 febbraio
ore 16
Massimo Inguscio
Presidente INRIM
L'Istituto Nazionale di Ricerca Metrologica (INRIM): una presentazione

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3 febbraio
ore 15
Luca Zilberti
Induzione Elettromagnetica, un fenomeno semplice... ma non banale
(Storia, curiosità, paradossi, formulazioni ed interpretazioni attorno alla legge di Faraday)

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Scoperta da Faraday (e, pressoché contemporaneamente, da Henry) nel 1831, l'induzione elettromagnetica è il principio alla base di innumerevoli realizzazioni tecnologiche di uso comune. A dispetto di tale versatilità applicativa, la rappresentazione modellistica di questo fenomeno è tuttavia apparsa critica fin dagli albori dell'elettrotecnica, come testimoniato dai vari esempi di "paradossi" che sembrano smentire la validità della legge usata per descriverlo. Nel corso del seminario si discuteranno alcuni di questi paradossi, insieme agli approcci che sono stati proposti per risolverli, nonché alle più recenti revisioni del problema, atte ad individuare una sua formulazione dall'efficacia generale. Infine saranno proposte riflessioni sull'interpretazione causale dell'induzione elettromagnetica, che ne costituisce un ulteriore aspetto sfuggente. L'intera presentazione sarà scandita da citazioni tratte direttamente dalle opere di alcuni dei "giganti" che hanno contribuito alla costruzione dell'Elettrodinamica Classica.
3 febbraio
ore 10:30
Joachim Ullrich
Presidente Physikalisch-Technische Bundesanstalt (PTB)
Metrology and Light - in the Year of Light and Beyond

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Metrology with and for light has been an ever-increasing field since the invention of the dynamo by W. v. Siemens in 1866 and of the carbon filament lamp by T. A. Edison in 1879. The foundation of the Physikalisch-Technische Reichsanstalt, PTR, in 1887 by H. v. Helmholtz and W. v. Siemens was among others strongly driven by the enormous growth of electric and lighting technologies in those days. Today we are facing a second revolution in light and lighting technologies with innovative laser-, LED- and OLED-source developments, the evolution of nano-photonics, single-photon and quantum-information technologies to name just a view with the quest for state-of-the-art metrology. In the future, light will play an even more important role for metrology with the advent of optical clocks, broad-band and high-precision optical fibre transmission technologies, methods to achieve spatial resolutions below the Abbe limit, with attosecond and free-electron-laser light sources coming online.
In the talk the fascination of light for mankind, the development of light and lightening technologies as well as present and future developments will be highlighted emphasizing in particular the challenges and opportunities for metrology in the future.
28 gennaio
ore 17
Maurizio Prato
Università degli Studi di Trieste
Synergies between Chemistry and Nanotechnology: Applications to Neurosciences and Energy

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Many problems of our times have not been solved yet, mostly due to the complexity of the problems and their difficult solutions. New approaches and new materials are therefore needed, to produce breakthroughs and generate new hopes. Among the wide range of novel materials available today, carbon nanotubes (CNTs) and graphene stand as unique materials for fundamental research and potential applications. During this talk, we will report on the most recent advances in our group, which have led to several interesting applications in many fields. For instance, functionalized carbon nanotubes stimulate neuronal communication or can serve as carriers for innovative drug delivery systems. On the other hand, carbon nanotubes and graphene are ideal supports for catalysis in water splitting devices, for the production of hydrogen as a clean source of energy.

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