61 research outputs found
Broadband characterization and time-resolved nanosecond magneto-optics of thin magnetic films
No full textIn the field of magnetic devices as in all the fields related to information technology and electronics the demand for a higher clock rate and faster device operations is continuously increasing. In data storage, the effort to reach the
highest information density is leading to the usage of patterned films having micrometer and sub-micrometer features. Both data storage and telecommunication
fields are focusing on the magnetization switching behavior at the highest attainable frequency. For data storage it is necessary to obtain a high read/write speed, while for telecommunications a magnetization switching
in the sub-nanosecond range is important due to the equivalence with wave propagation frequencies in the GHz range, where current technologies operate.
Most investigations in these fields have been performed up to now in the frequency domain, where important results have been obtained starting from the identification of the ferromagnetic resonance and spinwave modes.
Ultra fast magnetization dynamics on the nano- and picosecond time scale thus plays and will continue to play an important role for a large variety of present and future applications of magnetic nanostructures. At this time scale,
magnetization dynamics is dominated by the damped precessional motion of the magnetization about the acting internal and external fields. It is usually described by the Landau-Lifshitz-Gilbert equation, the two main parameters
involved in it being the ferromagnetic resonance frequency and the phenomenological Gilbert damping parameter .
Very different requirements on the FMR frequency and the Gilbert damping parameter have to be met for different technological applications: microwave absorbers based on ferromagnetic nanoparticles require large damping,
whereas in general all applications related to memory storage require a very low Gilbert damping . For fast sensors or spin transfer torque memory cells the dynamical properties of the magnetic devices must be precisely matched to the specific application.
In ferromagnetic resonance experiments, forced precession oscillations of the magnetization are excited by means of a high-frequency magnetic field, which is provided either by a Vector Network Analyzer (VNA), which performs a frequency sweep at a fixed external magnetic eld and returns scattering
parameters from which the complex magnetic permeability component can be obtained, or by means of a microwave oscillator, in a setup called field-sweep FMR where the same information about complex permeability are obtained through a varying magnetic field, the oscillator providing a fixed frequency signal.
If, instead of the ac field, a dc step pulse field is applied, free precession oscillations are excited, which then decay under the damping action of eddy currents and spin relaxation mechanisms. This is what is referred to as Pulsed
Inductive Microwave Magnetometer (PIMM), i.e. to a setup where the waveguide is used both as a source of fast pulsed magnetic fields and as an inductive flux sensor. The pulses are provided by a pulse generator, and a 20 GHz digital
sampling oscilloscope is used to acquire the fast pulse data. The system provides direct information on the dynamical behavior of the magnetization as a function of several variables, including applied magnetic bias field, magnetic
pulsed field amplitude and width, and sample orientation.
This thesis work is devoted to the experimental broadband investigation of several types of thin plates, films and multilayer samples in a wide frequency range, from DC up to several tens of GHz, and to the physical interpretation of
the material behavior upon such a wide frequency range and in particular to the development of experimental setups for the aforementioned characterizations
Fluxmetric-magnetooptical approach to broadband energy losses inamorphous ribbons
No full textThe magnetization process in field annealed amorphous ribbons has been investigated from dc to 10 MHz. Loss and permeability measurements, carried out both on single strips and ring samples by means of a broadband fluxmetric setup, have been associated with observations of the domain wall dynamics by high-speed stroboscopic Kerr apparatus. Transverse anisotropy Co-based ribbons exhibit a combination of rotational and domain wall processes, the latter being observed to progressively damp with frequency and coming to a halt on approaching the megahertz range. Given the vanishing direct contribution of the domain walls to the high-frequency magnetization process, the so-called classical loss formulation, associated with the rotational magnetization processes, is expected to correspondingly hold for the energy loss W(f). Under these conditions, W(f) tends to increase linearly with f, which, in view of the expected surge of the skin effect, does not agree with the f1/2 behavior accordingly predicted by standard formulas. This points to the specific properties of the rotational process and the role played by the exchange torque in connection with incomplete flux penetration
Magnetization Process in Thin Laminations up to 1 GHz
No full textAmorphous and nanocrystalline ribbons with transverse anisotropy have been characterized by magneto-optical, fluxmetric, and transmission line techniques from DC to 1 GHz. The contributions of domain wall displacements and magnetization rotations to the magnetization process, singled out by direct domain observations, consistently fit with the observed dependence of complex permeability and energy losses on frequency. With the domain wall motion suffering progressive hindering with increasing frequency and falling into full relaxation on reaching the MHz range, the magnetization process becomes amenable to a classical description, the concept of loss decomposition being secured. For this description, the conventional rate-independent constitutive relation for the magnetic material proves, however, inadequate. The diffusion equation for the electromagnetic field is therefore coupled with the Landau-Lifshitz-Gilbert equation, taken as a dynamic constitutive magnetic equation, and a solution is worked out by a numerical procedure. Magnetization and eddy-current field are thus obtained versus time at any point of the lamination, account being taken of the exchange field and its restraining action on the skin effect. The so calculated magnetic loss behavior turns out to correctly describe the high-frequency results, while coalescing with the classical eddy-current loss prediction at low frequencie
Domain wall processes, rotations, and high-frequency losses in thin laminations
No full textWe have investigated and modeled the magnetization process in thin amorphous and nanocrystalline ribbons from DC to 1 GHz. These transverse anisotropy laminations, their thickness ranging between 6 and 20 μm, display excellent broadband magnetic behavior, ensuing from the dominant role of magnetization rotations. Combination of fluxmetric, aftereffect, and high-speed magneto-optical experiments put in evidence that the domain wall processes, the obvious source of losses at low and medium frequencies in spite of negligible contribution to the magnetization reversal, fully damp on attaining the MHz range. Here the energy dissipation chiefly descends from the rotations and conforms to the so-called classical regime. To describe the high-frequency spin dynamics, the coupled Maxwell and Landau-Lifshitz-Gilbert equations are therefore considered. We have worked out a numerical solution of such equations by a finite element approach, based on a very fine time discretization and a computing scheme preserving the magnetization modulus. From the calculation of hysteresis loop and eddy current density at each mesh point, the separate contributions to the rotational losses by the eddy currents and the spin damping mechanism are obtained. The overall energy loss behavior versus frequency is thus eventually predicted in terms of separate contributions by the domain wall processes and the rotations
Ambra o la incertidumbre. El Financiero, sección Cultura "Clicks a la distancia"
No full textReferencias bibliográficas:Nulla OstaNota sobre el libro Nulla Ostra de Ambra Polidori, editado por Casa de las Imágenes y presentado el 7 de febrero del 2002 en el Museo Carrillo Gil por José Antonio Rodríguez y otros
Domestic Workers' Occupational Safety and Health in Italy: from Legal Gaps to Platform-Mediated Work
No full textThe essay deals with the protection of domestic workers’ occupational safety and health, namely an issue that deserves renewed attention considering the social importance of this type of work, the high risk of the sector as well as its evolution also through digital platforms. The author provides an overview of the regulation on the subject, starting with the international legal system and the European Union system up to the national system, focusing on the speciality of the domestic work relationship, the unvaried exclusion from the national prevention regulation, the measures by the pandemic emergency legislation and the missed novelties of the Decree Law No. 48/2023
Viaje e identidad en Atenas de Juan Vicente Piqueras
No full textIn this article, we propose an analysis of Juan Vicente Piqueras’ Atenas (2013), book that won the prestigious prize XXV Premio Fundación Loewe. Based on his experience in the Greek city, where he lived from 2007 to 2012, the author proposes a meditation on the theme of travel as a source of knowledge and on the condition of the postmodern human being by mixing myth with reality.En este artículo se propone un análisis de Atenas (2013) de Juan Vicente Piqueras, libro que obtuvo el XXV Premio Fundación Loewe. A partir de su experiencia en la ciudad griega, donde vivió desde 2007 hasta 2012, el poeta desarrolla una reflexión sobre el viaje como fuente de conocimiento y sobre la condición del individuo postmoderno, mezclando el mito con la realidad
Gloria Fuertes: sconfinare
No full textLa censura franchista, in vigore, in Spagna, a partire dagli anni Trenta, interviene su ogni manifestazione o prodotto culturale dell’epoca, con l’intento di diffondere l’ideologia promossa dal franchismo, mettendo a tacere qualunque possibile espressione di dissenso. Il presente lavoro si prefigge di analizzare la controversa figura della poetessa spagnola Gloria Fuertes, la quale, nonostante sia stata lungamente discriminata e confinata nell’ambito ristretto di una letteratura ritenuta marginale, è stata in grado di valicare i limiti imposti dal sistema egemonico e ritagliarsi uno spazio sacro di stridente resistenza antifranchista.
Dopo una breve premessa sul concetto di confine e alcuni essenziali cenni biografici, quindi, ci si focalizza prima sulle discriminazioni subite dall’autrice e, dopo, sulla sua sperimentazione di nuove forme e dispositivi narrativi che si rivelano capaci, sotto l’occhio disattento del lettore, di opporsi al discorso ufficiale promosso dal regime ribaltandone i presupposti teorici a favore di un’ideologia liberale e pacifista.During the Franco regime censorship acts on every demonstration or cultural
work to spread the ideology promoted by Francoism, silencing any possible
dissent. This work aims at analysing the controversial Spanish poet Gloria
Fuertes who succeeded in crossing the lines imposed by hegemonic system
and carved out her sacred space of anti-francoist resistance, although she had
been discriminated for so long and confined within the narrow context of literature
considered marginal. After a brief premise about border concept and
some essential biographical references, then, the attention at first focuses on
discriminations suffered by the author and secondly on her of new style and
narrative tools able to oppose to the official speech promoted by the regime
by overturning its theoretical assumptions in favour of a liberal and pacifist
ideology
Jan Maruna - the author of my region
No full textNa začátku práce jsem autora blíže představila a následně analyzovala jeho tři romány: Ambra a moře v nás, Hrobník od Svatého Bartoloměje, Vlak do nebe.
Při rozboru textů jsem se zaměřila na téma, prostředí a čas, charakteristiku postav, kompozici, jazyk a jeho prostředky.
Práce je rozdělena do čtyř hlavních kapitol: Portrét Jana Maruny, Vybrané romány, Analýza struktury vybraných děl a Ostatní prozaická díla v kontextu Jana Maruny.Katedra českého jazyka a literaturyObhájenoAt the beginning of the thesis I introduced the author in more detail and subsequently analysed his three novels: Ambra a moře v nás, Hrobník od Svatého Bartoloměje, Vlak do nebe. When I was examining the texts I was focused on the topic, setting and time, characteristic of characters, composition, language and its devices. The Bachelor thesis is divided into 4 main chapters: Portrait of Jan Maruna, Chosen novels, Analysis of structure of chosen works and Other prosaic works in context of Jan Maruna
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