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Dissertations / Theses on the topic 'Magnetization'
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1
Gupta, P. "Study of negative magnetization, exchange bias and magnetization switching in rare earth chromites." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2015. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2042.
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Sorea, Stanescu Dana Elena. "Magnetization dynamics in magnetic nanostructures." Phd thesis, Université Joseph Fourier (Grenoble), 2003. http://tel.archives-ouvertes.fr/tel-00006021.
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En utilisant la technique pompe-sonde résolue en temps, nous avons étudié la dynamique de l'aimantation dans des couches minces magnétiques avec une résolution temporelle de 20ps. La pompe est constituée par les champs magnétiques de hautes fréquences induits par des impulsions de tension appliquées sur une ligne coplanaire. Comme sonde, nous avons utilisé l'effet Kerr magnéto-optique et l'effet magnéto-résistif. Nous présentons la préparation des échantillons en utilisant le dépôt de couches minces par pulvérisation cathodique, la lithographie UV, ainsi que différentes techniques de gravure. Les résultats sur la dynamique de l'aimantation correspondent au régime des petites perturbations (de type Résonance Ferromagnétique) et à celui des grandes perturbations (ex. le renversement de l'aimantation). Nous avons mis en évidence le renversement par précession dans des vannes de spin de taille micronique et dans des couches minces continues.
3
Xu, Lei. "Magnetization Dynamics at Elevated Temperatures." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/311342.
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The area of ultrafast (sub-nanosecond) magnetization dynamics of ferromagnetic elements and thin films, usually driven by a strong femtosecond laser pulse, has experienced intense research interest. In this dissertation, laser-induced demagnetization is theoretically studied by taking into account interactions among electrons, spins, and lattice. We propose a microscopic approach under the three temperature framework and derive the equations that govern the demagnetization at arbitrary temperatures.To address the question of magnetization reversal at high temperatures, the conventional Landau-Lifshitz equation is obviously unsatisfactory, since it fails to describe the longitudinal relaxation. So by using the equation of motion for the quantum density matrix within the instantaneous local relaxation time approximation, we propose an effective equation that is capable of addressing magnetization dynamics for a wide range of temperatures. The longitudinal and transverse relaxations are analyzed, magnetization reversal processes near Curie temperatures is also studied. Furthermore, we compared our derived Self-consistent Bloch equation and Landau-Lifshitz-Bloch equation in detail. Finally, the demagnetzation dynamics for ferromagnetic and ferrimagnetic alloys is studied by solving the Self-consistent Bloch equation.
4
Rantaharju, J. (Jyrki). "Magnetization dynamics in paramagnetic systems." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526221205.
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This thesis reports simulations of direct observables in electron and nuclear spin relaxation experiments in an example paramagnetic system, as well as polarization transfer occurring in a spin-exchange optical pumping (SEOP) experiment. Studies of paramagnetic relaxation are important, e.g., in the development of agents used for enhanced contrast in magnetic resonance imaging. SEOP is used to produce hyperpolarized noble gases, which are then used to, e.g., enhance sensitivity in structural studies of matter with nuclear magnetic resonance. Presently the theory, available software and hardware for such computational modeling have reached a state in which quantitative reproduction of the experimentally observed magnetization decay is possible from first principles.
The present multiscale computations are carried out from first principles combining molecular dynamics simulations of atomistic motion and quantum-chemical electronic structure calculations of the spin interaction parameters that enter the effective spin Hamiltonian. A time series of the spin Hamiltonian is then explicitly used to propagate spin dynamics in the system, and dynamical time constants of the magnetization are obtained through ensemble averaging. The complete decay of electron spin magnetization could be followed directly within the duration of the simulation, whereas the nuclear spin relaxation rates were extracted using Kubo’s theory regarding generalized cumulant expansion and stochastic processes.
The extracted electron and nuclear spin relaxation rates for the chosen prototypic system, the aqueous solution of Ni²⁺, are in quantitative and semi-quantitative agreement, respectively, with the available experimental results. The simulations of polarization transfer corroborate the empirical observations on the importance of van der Waals complexes and binary collisions in the spin-exchange process. Long van der Waals complexes represent the overwhelmingly most significant kind of individual events, but the short binary collisions can also give a relatively important contribution due to their vast abundance. This thesis represents a first study in which first principles-calculated trajectories of individual events could be followed.
The simulations reported in this thesis were run without any empirical parametrization and thus represent a significant step in first-principles computational modeling of magnetization dynamics.
5
Méndez, Édgar. "Effective Visualization of Magnetization Dynamics." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-372080.
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Simulations on magnetization dynamics are of great interest on current research. Unlike computational fluid dynamics, magnetization dynamics has not received much attention from the visualization community. In this work a design and preliminary implementation of a visualization tool for magnetization dynamics simulations is introduced, based on methods used in the literature of the field. Although immature, the introduced design and implementation provide some advantages over some tools in use, and further development could lead to a unified and complete visualization utility.
6
Neudecker, Ingo. "Magnetization dynamics of confined ferromagnetic systems." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980172160.
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Kirste, Alexander. "Magnetization measurements in ultrahigh magnetic fields." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972633928.
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Krone, Philipp. "Magnetization Reversal Processes of Nanostructure Arrays." Doctoral thesis, Universitätsbibliothek Chemnitz, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-71358.
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In the thesis at hand, different concepts of magnetic recording were investigated both from an experimental and theoretical point of view. On the one hand, micromagnetic simulations of bit patterned media were performed examining the influence of magnetic and geometrical parameters on the magnetization reversal mechanism of the bit array. In this regard, the recording concept called exchange coupled composite (ECC) media was applied in combination with bit patterned media (BPM). It was demonstrated that ECC/BPM is superior in terms of narrowing the SFD which is vital for the implementation of BPM as a recording scheme in magnetic data storage deviced. Moreover, the stability of the magnetic state was calculated for single nanomagnets using the nudged elastic band algorithm. It was found out that the magnetic and geometrical properties have a severe influence on both, the energy barrier for magnetization reversal and the magnetization reversal process of the single nanomagnets. On the other hand, experimental studies of granular CoCrPt:SiO2 films deposited on self-assembled arrays of SiO2 nanoparticles with a size from 10 nm to 330 nm have been carried out, showing a distinct size-dependence of the coercive field and remanent magnetization with changing nanoparticle size. Moreover, these films have been irradiated with Co+ ions with different fluences, resulting in a change of the magnetic properties of the films due to both a change of the intergranular exchange coupling of the film and a degredation of the magnetic layers at higher irradiation fluences.
9
Chess, Jordan J. "Mapping Topological Magnetization and Magnetic Skyrmions." Thesis, University of Oregon, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10684160.
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<p> A 2014 study by the US Department of Energy conducted at Lawrence Berkeley National Laboratory estimated that U.S. data centers consumed 70 billion kWh of electricity. This represents about 1.8% of the total U.S. electricity consumption. Putting this in perspective 70 billion kWh of electricity is the equivalent of roughly 8 big nuclear reactors, or around double the nation's solar panel output. Developing new memory technologies capable of reducing this power consumption would be greatly beneficial as our demand for connectivity increases in the future. One newly emerging candidate for an information carrier in low power memory devices is the magnetic skyrmion. This magnetic texture is characterized by its specific non-trivial topology, giving it particle-like characteristics. Recent experimental work has shown that these skyrmions can be stabilized at room temperature and moved with extremely low electrical current densities. This rapidly developing field requires new measurement techniques capable of determining the topology of these textures at greater speed than previous approaches. In this dissertation, I give a brief introduction to the magnetic structures found in Fe/Gd multilayered systems. I then present newly developed techniques that streamline the analysis of Lorentz Transmission Electron Microscopy (LTEM) data. These techniques are then applied to further the understanding of the magnetic properties of these Fe/Gd based multilayered systems. </p><p> This dissertation includes previously published and unpublished co-authored material.</p><p>
10
Levesque, Ives. "Magnetization transfer imaging of multiple sclerosis." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79030.
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Magnetization transfer (MT) imaging is a magnetic resonance imaging techniqu ewhich permits indirect observation of the macromolecular component of biological tissue. Semi-quantitative implementations such as magnetization transfer ratio (MTR) imaging are very useful in the study of neuro-degenerative diseases, despite the relatively limited information provided by such single measurement methods. Quantitative techniques provide estimated measures of model parameters that more accurately describe the MT process. This thesis presents the application of quantitative MT imaging in a cross-sectional study of multiple sclerosis (MS) patients and healthy controls, exploring the on-going changes that occur in MS. Quantitative results are investigated to determine which model parameters play a role in the MTR. The findings demonstrate regional variations in white matter structures, and significant differences between healthy and normal-appearing MS tissue. The results also indicate the dominant role of macromolecular content in MTR, and confirm the destructive nature of T 1-hypointense lesions.
11
Schulze, Carsten. "Magnetization Reversal in Film-Nanostructure Architectures ." Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-142720.
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The concept of percolated perpendicular media (PPM) for magnetic data storage is expected to surpass the areal storage density of 1 Tbit in -², which is regarded as the fundamental limit of conventional granular CoCrPt:oxide based recording media. PPM consist of a continuous ferromagnetic thin film with densely distributed defects acting as pinning sites for magnetic domain walls.
In this study, practical realizations of PPM were fabricated by the deposition of [Co/Pt]8 multilayers with perpendicular magnetic anisotropy onto nanoperforated templates with various perforation diameters and periods. The structural defects given by the templates serve as pinning sites for the magnetic domain walls within the [Co/Pt]8 multilayers. Magnetometry at both the integral and the local level was employed to investigate the influence of the template on the magnetization reversal and the domain wall pinning.
It was found, that magnetic domains can be pinned at the ultimate limit, between three adjacent pinning sites. The coercivity and the depinning field, which both are a measure for the strength of the magnetic domain wall pinning, were found to increase with increasing perforation diameter. The size of magnetic domains within the magnetic film appeared not to depend solely on the diameter of the nanoperforations or on the period of the template, but on the ration between diameter and period. By means of micromagnetic simulations it was found, that the presence of ferromagnetic material within the pinning site given supports the pinning of magnetic domain walls, compared to a pinning site that is solely given by a hole in the magnetic thin film.
Investigation of the evolution of the magnetization in magnetic fields smaller than the coercive field revealed, that the energy barrier against thermally induced magnetization reversal is sufficiently large to provide long-term (> 10 years) stability of an arbitrary magnetization state. This could also be qualitatively supported by micromagnetic simulations.
Static read/write tests with conventional hard disk recording heads revealed the possibility of imprinting bit patterns into the PPM under study. The minimum bit pitch that could be read back thereby depended on the period of the nanoperforated template.
12
Berdahl, James Scott. "Remanent magnetization in angrite NWA 4931." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/114342.
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Thesis: S.B. in Geoscience, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 26-27).<br>Angrites are among the oldest known rocks and may record planetesimal dynamo activity and protoplanetary disk fields in the early solar system. Towards this goal, the natural remanent magnetism and its origin were examined in newly discovered angrite NWA 4931. Measurements were conducted on subsamples cut from various distances along a drilled core sample of the meteorite. The samples were then progressively demagnetized to isolate primary magnetization from contaminant overprints and to calculate paleofield intensity. Dust produced during the subsampling process was analyzed to determine that the mineralogical source of the magnetism was magnetite. Analyses of fusion crusted and adjacent samples showed that the exterior of the meteorite had been contaminated by a collector's hand magnet. However, the interior of the core yielded a pristine record, indicative of a paleointensity strength on the order of 25 [mu]T. These results, in light of magnetic measurements on other angrite samples, are suggestive of a core dynamo active for at least seven million years on the angrite parent body, beginning by 4564 Ma.<br>by James Scott Berdahl.<br>S.B. in Geoscience
13
Kesserwan, Hassan. "Ultrafast magnetization dynamics of magnetic nanostructures." Strasbourg, 2011. http://www.theses.fr/2011STRA6034.
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Divisé en deux parties, cette thèse décrit la dynamique d'aimantation de nanoparticules magnétiques. Dans la première partie, nous avons décrit une étude expérimentale détaillée de la dynamique d'aimantation dans des nanoparticules de CoPt sous forme de coeur/coquille. Pour cela, nous avons effectué des mesures d’effet Kerr magnéto-optique résolues en temps utilisant une pompe de 150 fs à 400 nm et une sonde de 150 fs à 800 nm. Nous avons étudié les différents processus qui ont lieu sur des échelles de temps bref : comme la démagnétisation ultrarapide et la précession du vecteur d’aimantation. Les résultats obtenus indiquent une possibilité d'induire un ordre supra-cristallin des nanoparticules par un recuit doux effectué par le faisceau laser absorbé par les nanoparticules. Nous avons montré qu’il y a une influence importante du recuit thermique sur les propriétés magnétiques des nanoparticules. Par exemple, ce recuit induit une transition de phase magnétique de super paramagnétique à ferromagnétique au dessus de la température ambiante. Ce ferromagnétisme se manifeste comme une augmentation de l’anisotropie magnétique des nanoparticules et par une précession du vecteur d’aimantation. La deuxième partie est consacrée à la simulation numérique des processus de renversement d'aimantation dans des nanoparticules isolées et en interaction. Dans les nanoparticules isolées, les temps de relaxation suivent la loi d'Arrhenius donnée par le modèle de Néel-Brown. Pour prendre en compte l'interaction magnétique dipolaire, nous avons introduit un modèle simple et efficace basé sur l'approximation de champ moyen. D’une manière générale, nous avons montré que l'interaction dipolaire accélère le processus de renversement d’aimantation<br>Divided in two parts, this PhD thesis concerns the magnetization dynamics of magnetic nanoparticles. In the first part, we have described a detailed experimental study of the magnetization dynamics in core/shell CoPt nanoparticles. Towards that goal, we have performed Time Resolved Magneto-Optical Effect measurements using a femtosecond pump and probe set-up with pulse durations and wavelengths : pump 150 fs/400 nm and probe 150 fs/800 nm probe. We studied the different magneto-dynamical processes taking place on short time scales such as : the ultrafast demagnetization and the precession of the magnetization vector. The obtained results indicate a possibility of inducing a supra-crystalline ordering of the nanoparticles due to a mild laser annealing. We showed that there is an important influence of the thermal annealing on the magnetic properties of the nanoparticles. For example, it leads to a magnetic phase transition form super-paramagnetic to ferromagnetic above the room temperature. This ferromagnetism manifested itself as an increase in the magnetic anisotropy of the nanoparticles and in the precession of the magnetization vector induced by the pump pulses. The second part is devoted to the numerical simulations of the magnetization reversal in isolated and interacting nanoparticles. In isolated nanoparticles, the relaxation times follow the Arrhenius law provided by the Néel-Brown’s model. To account for the magnetic dipolar interaction, we have introduced a simple and effective model based on the mean field approximation. In general, we have observed deviations from the Arrhenius law, and showed that the dipolar interaction accelerates the reversal process
14
Grassi, Matías Pablo. "Spin waves in inhomogeneous magnetization distributions." Thesis, Strasbourg, 2021. http://www.theses.fr/2021STRAE014.
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Des distributions inhomogènes de l’aimantation existent lorsque le matériau n’est pas uniforme, ou lorsqu’une texture magnétique se forme dans un matériau homogène. Dans les deux cas, les symétries brisées modifient l’excitation et la propagation des ondes de spin et donnent lieu à des phénomènes surprenants. Dans ce contexte, nous avons étudié la propagation des ondes de spin dans une bicouche avec un contraste de l’aimantation de saturation dans la configuration Damon-Eshbach. Nous avons trouvé, à l’aide de simulations et expériences (spectroscopie d'ondes de spin propagatives et diffusion de Brouillon), que le système montre une très forte non-réciprocité en fréquence qui peut être utilisée pour réaliser une diode magnonique. Par ailleurs, nous avons étudié la dynamique des ondes de spin dans des couches minces qui présentent des domaines magnétiques en rubans faibles. Nous avons montré que ces ondes de spin peuvent être interprétées comme une extension des modes de Damon-Eshbach dans l’état saturé, qui s’adaptent à la brisure de symétrie. Nous avons également montré que les deux modes d’ondes de spin de plus basse fréquence correspondent aux modes de Goldstone et Higgs de la texture en rubans. Ces résultats ont été confirmés par des mesures de diffusion Brillouin et de résonance ferromagnétique<br>Inhomogeneous magnetization distributions may exist because the magnetic parameters are distributed, or because magnetic textures nucleate in homogenous materials. In both cases, the broken symmetries affect the spin-wave excitation and propagation, leading to a number of intriguing phenomena. In this context, we have studied the propagation of spin waves in a bilayer with a saturation magnetization contrast for the Damon-Eshbach configuration. We have found, by means of simulations and experiments (Propagating Spin Wave Spectroscopy and Brillouin Light Scattering), that this system shows a strong frequency non-reciprocity which can be used for the realization of a spin-wave diode. We have also studied the spin-wave dynamics in thin films which exhibit weak magnetic stripe domains. We have shown how these modes can be interpreted as an extension of the Damon-Eshbach spectrum of the saturated state, which adapts to the symmetry breaking. Furthermore, we have identified the two lowest frequency modes to the Goldstone- and Higgs- modes of the stripe texture. These results were confirmed by Brillouin Light Scattering and Ferromagnetic Resonance experiments
15
Wang, Suqin. "Magnetization dynamics of single domain nanomagnets /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2007. http://uclibs.org/PID/11984.
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Lu, Shu. "Power transformer magnetization under GIC/GMD." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-09232008-144706/.
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Rumberger, Evan Michael Wong. "Magnetization dynamics in single-molecule magnets /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3153694.
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Chess, Jordan. "Mapping topological magnetization and magnetic skyrmions." Thesis, University of Oregon, 2018. http://hdl.handle.net/1794/23188.
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A 2014 study by the US Department of Energy conducted at Lawrence Berkeley National Laboratory estimated that U.S. data centers consumed 70 billion kWh of electricity[1]. This represents about 1.8% of the total U.S. electricity consumption. Putting this in perspective 70 billion kWh of electricity is the equivalent of roughly 8 big nuclear reactors, or around double the nation's solar panel output[2]. Developing new memory technologies capable of reducing this power consumption would be greatly beneficial as our demand for connectivity increases in the future. One newly emerging candidate for an information carrier in low power memory devices is the magnetic skyrmion. This magnetic texture is characterized by its specific non-trivial topology, giving it particle-like characteristics.
Recent experimental work has shown that these skyrmions can be stabilized at room temperature and moved with extremely low electrical current densities. This rapidly developing field requires new measurement techniques capable of determining the topology of these textures at greater speed than previous approaches. In this dissertation, I give a brief introduction to the magnetic structures found in Fe/Gd multilayered systems. I then present newly developed techniques that streamline the analysis of Lorentz Transmission Electron Microscopy (LTEM) data. These techniques are then applied to further the understanding of the magnetic properties of these Fe/Gd based multilayered systems.
This dissertation includes previously published and unpublished co-authored material.
19
Uhlíř, Vojtěch. "Current Induced Magnetization Dynamics in Nanostructures." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-233903.
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Předkládaná dizertační práce pojednává o problematice pohybu doménových stěn (DS) vyvolaného spinově polarizovaným proudem v magnetických nanodrátech na bázi spinového ventilu NiFe/Cu/Co. Jedná se o tzv. efekt přenosu spinového momentu. Multivrstevnatý systém NiFe/Cu/Co, kde se doménová stěna pohybuje ve vrstvě NiFe, vykazuje velmi vysokou účinnost přenosu spinového momentu, což bylo v literatuře potvrzeno na základě magnetotransportních měření. Tato práce má za cíl pozorovat stav DS během jejich pohybu, pomocí fotoelektronové mikroskopie kombinované s kruhovým magnetickým dichroismem. Tato technika využívá synchrotronové záření, které svým časovým rozlišením umožňuje sledovat dynamickou odezvu magnetizace na elektrický proud. Podstatnou částí řešení byla optimizace růstu vrstev NiFe/Cu/Co kvůli snížení magnetické dipolární interakce mezi vrstvami. V práci je také řešen způsob přípravy nanodrátů litografickými metodami. Byly provedeny dva módy měření: i) kvazistatický, tj. pozorování DS před a po injekci proudu do nanodrátu a ii) dynamické měření, kde je DS sledována během působení proudového pulzu. S využitím kvazistatickém módu byla vypracována rozsáhlá statistika pohybu DS: i) byly naměřeny jejich vysoké rychlosti přesahující 600 m/s za působení průměrné proudové hustoty nutné k posuvu doménové stěny - 5x10^11 A/m^2; ii) DS jsou v systému NiFe/Cu/Co velmi silně zachycovány dipolární interakcí mezi NiFe a Co způsobenou nehomogenitou krystalové struktury ve vrstvě Co. V dynamickém módu bylo odhaleno, že působením Oerstedovského pole kolmého na nanodráty v rovině vzorku se magnetizace ve vrstvě NiFe silně natáčí. Tento efekt přispívá k vysokým rychlostem DS pozorovaných v nanodrátech NiFe/Cu/Co.
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Kneip, Martin K. "Magnetization dynamics in diluted magnetic semiconductor heterostructures." kostenfrei, 2008. http://hdl.handle.net/2003/25822.
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Mondal, Ritwik. "Relativistic theory of laser-induced magnetization dynamics." Doctoral thesis, Uppsala universitet, Materialteori, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-315247.
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Ultrafast dynamical processes in magnetic systems have become the subject of intense research during the last two decades, initiated by the pioneering discovery of femtosecond laser-induced demagnetization in nickel. In this thesis, we develop theory for fast and ultrafast magnetization dynamics. In particular, we build relativistic theory to explain the magnetization dynamics observed at short timescales in pump-probe magneto-optical experiments and compute from first-principles the coherent laser-induced magnetization. In the developed relativistic theory, we start from the fundamental Dirac-Kohn-Sham equation that includes all relativistic effects related to spin and orbital magnetism as well as the magnetic exchange interaction and any external electromagnetic field. As it describes both particle and antiparticle, a separation between them is sought because we focus on low-energy excitations within the particle system. Doing so, we derive the extended Pauli Hamiltonian that captures all relativistic contributions in first order; the most significant one is the full spin-orbit interaction (gauge invariant and Hermitian). Noteworthy, we find that this relativistic framework explains a wide range of dynamical magnetic phenomena. To mention, (i) we show that the phenomenological Landau-Lifshitz-Gilbert equation of spin dynamics can be rigorously obtained from the Dirac-Kohn-Sham equation and we derive an exact expression for the tensorial Gilbert damping. (ii) We derive, from the gauge-invariant part of the spin-orbit interaction, the existence of a relativistic interaction that linearly couples the angular momentum of the electromagnetic field and the electron spin. We show this spin-photon interaction to provide the previously unknown origin of the angular magneto-electric coupling, to explain coherent ultrafast magnetism, and to lead to a new torque, the optical spin-orbit torque. (iii) We derive a definite description of magnetic inertia (spin nutation) in ultrafast magnetization dynamics and show that it is a higher-order spin-orbit effect. (iv) We develop a unified theory of magnetization dynamics that includes spin currents and show that the nonrelativistic spin currents naturally lead to the current-induced spin-transfer torques, whereas the relativistic spin currents lead to spin-orbit torques. (v) Using the relativistic framework together with ab initio magneto-optical calculations we show that relativistic laser-induced spin-flip transitions do not explain the measured large laser-induced demagnetization. Employing the ab initio relativistic framework, we calculate the amount of magnetization that can be imparted in a material by means of circularly polarized light – the so-called inverse Faraday effect. We show the existence of both spin and orbital induced magnetizations, which surprisingly reveal a different behavior. We establish that the laser-induced magnetization is antisymmetric in the light’s helicity for nonmagnets, antiferromagnets and paramagnets; however, it is only asymmetric for ferromagnets.
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Chandra, Sayan. "Magnetization Dynamics and Related Phenomena in Nanostructures." Thesis, University of South Florida, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3604829.
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<p> Collective magnetic behavior in nanostructures is a phenomenon commonly observed in various magnetic systems. It arises due to competing inter/intra&ndashparticle; interactions and size distribution and can manifest in phenomena like magnetic freezing, magnetic aging, and exchange bias (EB) effect. In order to probe these rather complex phenomena, conventional DC and AC magnetic measurements have been performed along with radio&ndashfrequency; transverse susceptibility (TS) measurements. We also demonstrate the magnetic entropy change as a parameter sensitive to subtle changes in the magnetization dynamics of nanostructures. The focus of this dissertation is to study the collective magnetic behavior in core-shell nanostructures of Fe/γ&ndashFe;<sub>2</sub>O<sub>3</sub> and Co/CoO, La<sub>0.5</sub>Sr<sub>0.5</sub>MnO<sub>3</sub> nanowires, and LaMnO<sub>3</sub> nanoparticles.</p><p> In the case of core/shell Fe/γ&ndashFe;<sub>2</sub>O<sub>3</sub>, we found the particles to critically slow down below the glass transition temperature, below which they exhibit aging effects associated with a superspin glass (SSG) state. We demonstrate that it is possible to identify individual magnetic responses of the Fe core and the γ&ndashFe;<sub>2</sub>O<sub> 3</sub> shell. Consistently, a systematic study of the magnetocaloric effect (MCE) in the Fe/γ&ndashFe;<sub>2</sub>O<sub>3</sub> system reveals the development of inverse MCE with peaks associated with the individual magnetic freezing of the core and the shell. From these obtained results, we establish a general criterion for EB to develop in core/shell nanostructures, that is when the core is in the frozen state and the magnetic moments in the shell begin to block. This criterion is shown to be valid for both ferromagnetic/ferrimagnetic (FM/FIM) Fe/γ&ndashFe;<sub>2</sub>O<sub>3</sub> and ferromagnetic/antiferromagnetic (FM/AFM) Co/CoO core&ndashshell; nanostructures. We also elucidate the physical origin of the occurrence of asymmetry in field-cooled hysteresis loops and its dependence on magnetic anisotropy in the Co/CoO system by performing a detailed TS study.</p><p> We have performed a detailed magnetic study on hydrothermally synthesized single crystalline La<sub>0.5</sub>Sr<sub>0.5</sub>MnO<sub>3</sub> nanowires. The temperature and field dependent evolution of the different magnetic phases leading to development of the inverse MCE and EB in the nanowires is discussed. Finally, we have studied the collective magnetic behavior of LaMnO<sub>3</sub> nanoparticles synthesized by the sol&ndashgel; technique. The nanoparticle ensemble shows the unusual co&ndashexistence; of super-ferromagnetism (SFM), as well as the SSG state, which we term the &lsquoferromagnetic; superglass’ (FSG) state. The existence of FSG and the characteristics of its magnetic ground state are discussed.</p>
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Chandra, Sayan. "Magnetization Dynamics and Related Phenomena in Nanostructures." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4877.
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Collective magnetic behavior in nanostructures is a phenomenon commonly observed in various magnetic systems. It arises due to competing inter/intra–particle interactions and size distribution and can manifest in phenomena like magnetic freezing, magnetic aging, and exchange bias (EB) effect. In order to probe these rather complex phenomena, conventional DC and AC magnetic measurements have been performed along with radio–frequency transverse susceptibility (TS) measurements. We also demonstrate the magnetic entropy change as a parameter sensitive to subtle changes in the magnetization dynamics of nanostructures. The focus of this dissertation is to study the collective magnetic behavior in core-shell nanostructures of Fe/γ–Fe2O3 and Co/CoO, La0.5Sr0.5MnO3 nanowires, and LaMnO3 nanoparticles.
In the case of core/shell Fe/γ–Fe2O3, we found the particles to critically slow down below the glass transition temperature, below which they exhibit aging effects associated with a superspin glass (SSG) state. We demonstrate that it is possible to identify individual magnetic responses of the Fe core and the γ–Fe2O3 shell. Consistently, a systematic study of the magnetocaloric effect (MCE) in the Fe/γ–Fe2O3 system reveals the development of inverse MCE with peaks associated with the individual magnetic freezing of the core and the shell. From these obtained results, we establish a general criterion for EB to develop in core/shell nanostructures, that is when the core is in the frozen state and the magnetic moments in the shell begin to block. This criterion is shown to be valid for both ferromagnetic/ferrimagnetic (FM/FIM) Fe/γ–Fe2O3 and ferromagnetic/antiferromagnetic (FM/AFM) Co/CoO core–shell nanostructures. We also elucidate the physical origin of the occurrence of asymmetry in field-cooled hysteresis loops and its dependence on magnetic anisotropy in the Co/CoO system by performing a detailed TS study.
We have performed a detailed magnetic study on hydrothermally synthesized single crystalline La0.5Sr0.5MnO3 nanowires. The temperature and field dependent evolution of the different magnetic phases leading to development of the inverse MCE and EB in the nanowires is discussed. Finally, we have studied the collective magnetic behavior of LaMnO3 nanoparticles synthesized by the sol–gel technique. The nanoparticle ensemble shows the unusual co–existence of super-ferromagnetism (SFM), as well as the SSG state, which we term the 'ferromagnetic superglass' (FSG) state. The existence of FSG and the characteristics of its magnetic ground state are discussed.
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Wittmann, Andreas. "Magnetoresistance and magnetization dynamics in hybrid structures." München Verl. Dr. Hut, 2008. http://d-nb.info/991285271/04.
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Zhang, Zhen. "Magnetization reversal in a soft magnetic nanowire /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MATH%202009%20ZHANG.
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Chettouh, Louiza. "Investigating thermally assisted controlof magnetization using plasmons." Thesis, Uppsala universitet, Materialfysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388253.
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Adams, Daniel J. "Magnetization Dynamics in Coupled Thin Film Systems." ScholarWorks@UNO, 2019. https://scholarworks.uno.edu/td/2578.
Full textAbstract:
A study is presented detailing experimental investigations of magnetization dynamics in nanostructured systems which are coupled magnetically. This work seeks to characterize the anisotropy of such systems through experimental techniques which probe microwave resonant absorption in the materials.
A custom-built experimental setup, designed and assembled in our labs, is explained in detail. This setup allows for angular-dependent ferromagnetic resonance (FMR) measurements in the sample plane through vector network analyzer spectroscopy and is adaptable to two different types of coplanar waveguides. This technique has proven effective for characterization of multiple types of magnetic systems, including multilayered structures as detailed here, with different types of anisotropies while allowing us to draw analogies with more common characterization techniques. The angular FMR setup has been used to study coupled systems, such as those coupled through the Ruderman–Kittel–Kasuya–Yosida interaction as well as exchange-biased structures. These types of coupled systems have technological impacts and are highly applied in the components of magnetoresistive random access memory. Using this new characterization technique, properties of synthetic antiferromagnets have been revealed which had not been observed before.
In addition to these experiments, magnetic susceptibility and FMR in exchange biased systems have been investigated at temperatures as low as 2 K. This investigation used a new FMR spectrometer and was one of the first studies to use this instrument.
For the first time a new method of identifying several types of coupling which can be present in layered nanostructures is presented and supported through comparison with known techniques, thus connecting a new characterization technique for layered structures with decades-old procedures. Many results within this work are also supported theoretically with computer simulations.
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Totland, Karin. "Induced magnetization in metallic adlayers on Fe(100) /." [S.l.] : [s.n.], 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10481.
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Borlenghi, Simone. "Electronic transport and magnetization dynamics in magnetic systems." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2011. http://tel.archives-ouvertes.fr/tel-00590363.
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L'objectif de ce travail de thèse est de comprendre l'influence mutuelle entre le transport électronique et la dynamique de l'aimantation dans des nanostructures hybrides magnétiques métalliques. Dans une première partie on a développé un modèle théorique, basé sur la théorie des matrices aléatories, pour décrire au niveau microscopique le transport dépendent du spin dans une nanostructure hétérogène. Ce modèle, appélé CRMT (pour Continuous Random Matrix Theory) a ensuite été traduit dans un code de simulation qui permet de calculer les proprietés locales (couple de transfert de spin, accumulation de spin et courant de spin) et macroscopiques (résistance) du transport dans des conducteurs ohmiques. Le modèle a été validé en le comparant avec une théorie du transport quantique basée sur le calcul des fonctions de Green hors équilibre. Le couplage des ce deux modèles a permis d'effectuer une description multiéchelle du transport dans des nanostructures métalliques hybrides, où les parties ohmiques sont décrites par CRMT et les parties purement quantiques par le formalisme des fonctions de Green. CRMT a ensuite été incorporé dans un code de simulation micromagnétique, pour décrire de façon réaliste la texture spatiale de la dynamique de l'aimantation induite par le transfert de spin. L'originalité de cette approche réside dans la modélisation des mesures spectroscopiques utilisant une détection mécanique de la résonance ferromagnétique, conduites sur des oscillateurs à transport de spin. Ce travail a permis d'obtenir le diagramme de phase dynamique de l'aimantation, ainsi que les règles de sélection des ondes de spin et la compétition entre les modes propres du systeme lors du passage d'un courant continu à travers la multicouche, en accord partiel avec les données experimentales
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Mousavi, Seyed Ali. "Electromagnetic Modelling of Power Transformers with DC Magnetization." Licentiate thesis, KTH, Elektroteknisk teori och konstruktion, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105395.
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DC currents that flow through the ground can be injected to the star windings of power transformers from their grounded neutral points and close their path with transmission lines. The geomagnetically induced currents (GICs) and AC/DC convertors of high voltage direct current (HVDC) systems are the sources of such DC currents. These currents may cause saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomenon results in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and misoperation of protective relays menaces the power network. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC. Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis. In this project until now, a new algorithm for digital measurement of the core materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Three dimensional finite element models of various core types of power transformers are created to study the effect on them due to DC magnetization. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a distributed reluctance network method has been outlined. In this thesis a method for solving such a network problem with coupling to an electrical circuit and taking hysteresis into account is suggested.<br><p>QC 20121121</p>
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Alekhin, Alexandr [Verfasser]. "Ultrafast hot carrier driven magnetization dynamics / Alexandr Alekhin." Berlin : Freie Universität Berlin, 2016. http://d-nb.info/1088402275/34.
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Binder, Michael. "Magnetization dynamics of rare earth doped magnetic films." Berlin Logos-Verl, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?id=2917185&prov=M&dok_var=1&dok_ext=htm.
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Binder, Michael. "Magnetization dynamics of rare-earth doped magnetic films /." Berlin : Logos-Verl, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=2917185&prov=M&dok_var=1&dok_ext=htm.
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Neufeldt, Bryan. "A pulsed magnet for high-field magnetization measurements /." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61254.
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The design and construction of a capacitor-discharge pulsed magnet is described. The magnet is capable of generating peak fields up to 22 T in a multi-turn solenoid coil with a 3/4" (19 mm) bore. The coil design, calculation of peak field, and an analysis of the eddy currents in the metal surrounding the coil are discussed in detail. The pulsed magnet includes a magnetometer and a data acquisition system which measure the coil field and sample magnetization. A series of magnetization curves have been obtained for a sample of Nd$ rm{ sb2 Fe sb{14} B}$.
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Jones, J. Nicholas. "Flux creep and magnetization in high temperature superconductors." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307081.
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Kendall, Danny. "Magnetization processes and the magnetomechanical properties of Terfenol." Thesis, University of Brighton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293327.
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Meng, Tiejun. "Magnetization properties and magnetotransport of cobalt nano-structures." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611529.
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Lorite, Israel, Yogesh Kumar, Pablo Esquinazi, et al. "Photo-enhanced magnetization in Fe-doped ZnO nanowires." American Institute of Physics, 2016. https://ul.qucosa.de/id/qucosa%3A31213.
Full textAbstract:
An emerging branch of electronics, the optospintronics, would be highly boosted if the control of
magnetic order by light is implemented in magnetic semiconductors’ nanostructures being
compatible with the actual technology. Here, we show that the ferromagnetic magnetization of low
Fe-doped ZnO nanowires prepared by carbothermal process is enhanced under illumination up to
temperatures slightly below room temperature. This enhancement is related to the existence of an
oxygen vacancy VO in the neighborhood of an antiferromagnetic superexchange Fe3+-Fe3+ pair.
Under illumination, the VO is ionized to to V+O giving an electron to a closeFe3+ ion from the antiferromagnetic
pair. This light excited electron transition allows the transition of Fe3+ to Fe2+ forming
stable ferromagnetic double exchange pairs, increasing the total magnetization. The results presented
here indicate an efficient way to influence the magnetic properties of ZnO based nanostructures
by light illumination at high temperatures.
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Lu, Jie. "Field-driven magnetization dynamics of nanoparticles and nanowires /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202009%20LUJ.
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Bianco, Raffaello. "Chern invariant and orbital magnetization as local quantities." Doctoral thesis, Università degli studi di Trieste, 2014. http://hdl.handle.net/10077/9959.
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2012/2013<br>La geometria, e la topologia in particolare, rivestono un profondo ruolo in molti campi della fisica ed in particolare in materia condensata ove è possibile identificare diversi stati quantistici della materia attraverso proprietà topologiche. L'invariante di Chern è un invariante topologico
che caratterizza lo stato isolante dei cristalli. Esso è definito attraverso la descrizione in spazio reciproco di un cristallo perfetto, per cui
è necessario considerare un sistema infinito oppure finito ma con condizioni periodiche al bordo. In questa tesi il concetto di invariante di Chern
viene generalizzato definendo un opportuno marcatore locale di Chern in spazio reale. Infatti se si considera un cristallo perfetto infinito oppure finito e con condizioni periodiche al bordo, la media sulla cella elementare di questo marcatore restituisce il consueto invariante di Chern. Tuttavia, grazie al suo carattere locale, il marcatore di Chern è ben definito e può essere utilizzato per identificare il carattere
locale di Chern anche di un sistema microscopicamente disordinato o macroscopicamente disomogeneo (ad esempio etorogiunzioni di diversi cristalli) e
con qualsiasi tipo di condizioni al bordo (periodiche o aperte).
Nella seconda parte della tesi l'invariante locale di Chern viene utilizzato per fornire una descrizione locale in spazio reale della magentizzazione
orbitale. Questa descrizione è utilizzabile sia con condizioni al bordo aperte che periodiche e quindi unifica i due separati approcci utilizzati
in questi due casi. La nuova formula permette, inoltre, di ottenere anche una migliore comprensione del ruolo che gli stati di bordo rivestono nella
magnetizzazione di un sistema. In entrambi i casi vengono presentati i risultati di simulazioni numeriche che confermano i risultati teorici
derivati.<br>The geometry and the topology play a profound role in many fields of physics and in particular in condensed matter where it is possible to identify different quantum states of matter through their topological properties. The Chern invariant is a topological invariant
which characterizes the insulating state of crystals. It is defined through the description in the reciprocal space of a perfect crystal, which
then has to be considered as an infinite system or a finite size system with periodic boundary conditions. In this thesis the concept of Chern invariant
is generalized by defining a local Chern marker in the real space. For an infinite crystal or a finite crystal with periodic boundary conditions, the average of this marker over an elementary unit cell returns the usual invariant Chern.
However, thanks to its local character, the Chern marker is well defined and can be used to identify the local Chern character
also of microscopically disordered systems or macroscopically inhomogeneous systems (e.g. heterojunctions of different crystals) and
with any kind of boundary conditions adopted (periodic boundary conditions or open bounday conditions as well).
In the second part of the thesis the local Chern invariant is used to provide a local description in the real space of the orbital magnetization. This description can be used both with open and periodic boundary conditions, so it unifies the two separate approaches used
in these different cases. Moreover, the new formula makes it possible to get a better understanding of the role that the edge states play
in the magnetization of a system. In both cases we present the results of numerical simulations that confirm the theoretical results.<br>XXVI Ciclo<br>1979
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Borlenghi, Garoia Simone. "Electronic transport and magnetization dynamics in magnetic systems." Paris 6, 2011. http://www.theses.fr/2011PA066009.
Full textAbstract:
L'objectif de ce travail de thèse est de comprendre l'influence mutuelle entre transport électronique et dynamique de l'aimantation dans des nanostructures hybrides magnétiques métalliques. Dans une première partie on a développé un modèle théorique, basé sur la théorie des matrices aléatories, pour décrire à niveau microscopique le transport dépendent du spin dans une nanostructure hétérogène. Ce modèle, appélé CRMT (Continuous Random Matrix Theory) a ensuite été traduit dans un code de simulation qui permet de calculer les proprietés locales (couple de transfert de spin, accumulation de spin et courant de spin) et globales (résistance) de transport dans des conducteurs ohmiques. Le modèle a été validé en le comparant avec une théorie du transport quantique basée sur le calcul des fonctions de Green hors équilibre (NEGF-Non Equilibrium Green Function formalism). Le couplage des ce deux modèles a permis d'éffectuer une description multi-échelle du transport dans des nanostructures métalliques hybrides, où les parties ohmiques sont décrites par CRMT (plus pérformant du point de vue computationnel) et les parties purement quantiques par le formalisme des fonctions de Green. CRMT a ensuite été couplé à un code de simulation micromagnétique, pour prendre en compte la dynamique complexe de l'aimantation induite par le transfert de spin. L'originalité de cette approche réside dans la modélisation des expériences de résonance ferromagnétique conduites sur des oscillateurs a transport de spin. Ce travail a permis la mise en évidence des règles de sélection des ondes de spin induites par le transfert de spin, en accord avec les données experimentales
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Kaushalya. "Ultrafast manipulation of magnetization using on-chip THz." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0173.
Full textAbstract:
Le besoin de dispositifs de stockage de mémoire a explosé au cours des dernières décennies, en particulier après le développement d'Internet. Ce besoin a atteint des sommets énormes au cours des deux dernières années, peu après la pandémie due au COVID-19. Les disques durs (HDD) sont connus pour avoir le potentiel de répondre aux demandes de stockage de données haute densité. Cette thèse traite de l'un des défis majeurs rencontrés au sein de la communauté spintronique pour améliorer la vitesse et la consommation d'énergie des dispositifs de mémoire. La vitesse de fonctionnement lors de l'écriture d'un bit magnétique dépend du mécanisme de commutation de magnétisation utilisé. Le mécanisme de commutation est lui-même dépendant des propriétés magnétiques intrinsèques de l'échantillon et de l'excitation induite de l'extérieur qui entraîne l'inversion du trépan magnétique 1. Dans cette thèse, nous nous concentrerons sur l'utilisation des excitations du couple spin-orbite (SOT) pour entraîner l'inversion, qui sont une approche relativement nouvelle mais rapide et économe en énergie par rapport à d'autres méthodes de pointe. La vitesse typique d'inversion de magnétisation à l'aide des SOT est de l'ordre de quelques nanosecondes, bien plus lente que la commutation longue de la picoseconde qui est possible avec les dispositifs de mémoire basés sur la charge 2. En fait, une vitesse d'inversion record avec des impulsions électriques aussi courtes que ~ 200 ps a été signalée par Garello et. al., 3 en 2011 en utilisant des SOT. Cette thèse rapporte des efforts supplémentaires pour accélérer l'inversion de l'aimantation de près de 2 ordres de grandeur en exploitant de tels SOT. Dans ce but, des impulsions électriques THz ont été générées via l'utilisation de commutateurs photoconducteurs Auston. Nous démontrons qu'une seule impulsion électrique de 6ps de large peut induire un SOT sur une couche ferromagnétique de Co d'une épaisseur de 1 nm et entraîner une inversion complète de l'aimantation. Une étude systématique pour comprendre les SOT dans le régime temporel picoseconde est également entreprise via l'utilisation de différentes nanostructures magnétiques. Dans les dispositifs à mémoire magnétique, une "tête de lecture" est utilisée pour lire les informations stockées dans le dispositif. Typiquement, dans les dispositifs spintroniques, des têtes de lecture à magnétorésistance géante (GMR) ou à magnétorésistance tunnel (TMR) sont utilisées pour de telles opérations. Dans cette thèse, nous rapportons également les tentatives de développement d'un capteur GMR fonctionnant en régime THz. Pour entreprendre les études susmentionnées, un montage expérimental optique et optoélectrique pompe-sonde a également été construit et un rapport détaillé de celui-ci est également fourni dans la thèse<br>The need for memory storage devices has skyrocketed over the last few decades especially after the development of the internet. This need has reached enormous heights in the past two years, soon after the pandemic due to COVID-19. Hard disk drives (HDDs) are known to have the potential to meet up with the high-density data storage demands. This thesis deals with one of the major challenges faced within the spintronic community to improve the speed and the energy consumption of memory devices.The speed of operation during the writing of a magnetic bit depends on the magnetization switching mechanism employed. The switching mechanism is itself dependent on the intrinsic magnetic properties of the sample and the externally induced excitation that drives the reversal of the magnetic bit 1. In this thesis, we will focus on the use of spin-orbit torque (SOT) excitations to drive the reversal, which is a relatively new but fast and energy-efficient approach in comparison with other state-of-the-art methods.The typical speed of magnetization reversal using SOTs is in the range of few nanoseconds, far slower than the picosecond-long switching that is possible with charge-based memory devices2. In fact, a record reversal speed with electrical pulses as short as ~200ps was reported by Garello et. al., 3 in 2011 using SOTs. This thesis reports further efforts to speed up the magnetization reversal by almost 2 orders of magnitude by exploiting such SOTs. To this aim, THz electrical pulses were generated via the use Auston photoconductive switches. We demonstrate that a single 6ps wide electrical pulse can induce a SOT to a 1nm thin Co ferromagnetic layer and result in a full magnetization reversal. A systematic study to understand SOTs in the picosecond time regime is also undertaken via using different magnetic nanostructures.In magnetic memory devices, a “read-head” is used to read the stored information in the device. Typically, in spintronic devices, giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) based read heads are used for such operations. In this thesis, we also report on the attempts of developing a GMR sensor working in the THz regime.To undertake the aforementioned studies, a pump-probe optical and optoelectrical experimental setup has also been built and a detailed report of the same is also provided in the thesis
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Schulze, Carsten [Verfasser], Manfred [Akademischer Betreuer] Albrecht, Manfred [Gutachter] Albrecht, and Sibylle [Gutachter] Gemming. "Magnetization Reversal in Film-Nanostructure Architectures : Magnetization Reversal in Film-Nanostructure Architectures / Carsten Schulze ; Gutachter: Manfred Albrecht, Sibylle Gemming ; Betreuer: Manfred Albrecht." Chemnitz : Universitätsbibliothek Chemnitz, 2014. http://d-nb.info/1214302173/34.
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Meier, Florian. "Coherent spin dynamics and magnetization transport in nanoscale magnetism /." [S.l.] : [s.n.], 2003. http://edoc.unibas.ch/diss/DissB_6468.
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Bran, Cristina. "Domain structure and magnetization processes of complex magnetic multilayers." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-33319.
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The magnetization processes of antiferromagnetically (AF) coupled Co/Pt multilayers on extended substrates and of Co/Pd multilayers deposited on arrays of 58 nm spheres are investigated via magnetic force microscopy at room temperature by imaging the domain configuration in magnetic fields. Adding AF exchange to such perpendicular anisotropy systems changes the typical energy balance that controls magnetic band domain formation, thus resulting in two competing reversal modes for the system. In the ferromagnetic (FM) dominated regime the magnetization forms FM band domains, vertically correlated. By applying a magnetic field, a transition from band to bubble domains is observed. In the AF-exchange dominated regime, by applying a field or varying the temperature it is possible to alter the magnetic correlation from horizontal (AF state) to vertical (FM state) via the formation of specific multidomain states, called metamagnetic domains. A theoretical model, developed for complex multilayers is applied to the experimentally studied multilayer architecture, showing a good agreement. Magnetic nanoparticles have attracted considerable interest in recent years due to possible applications in high density data storage technology. Requirements are a well defined and localized magnetic switching behavior and a large thermal stability in zero fields. The thermal stability of [Co/Pt]N multilayers with different numbers of repeats (N), deposited on nanospheres is studied by magnetic viscosity measurements. The magnetic activation volume, representing the effect of thermal activation on the switching process, is estimated. It is found that the activation volume is much smaller than the volume of the nanosphere and almost independent of the number of bilayers supporting an inhomogeneous magnetization reversal process.
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Bocklage, Lars [Verfasser]. "Current-Induced Magnetization Dynamics of Ferromagnetic Nanostructures / Lars Bocklage." München : Verlag Dr. Hut, 2011. http://d-nb.info/1016531605/34.
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Bohlens, Stellan [Verfasser]. "Interplay of Inhomogeneous Currents and Magnetization Textures / Stellan Bohlens." München : Verlag Dr. Hut, 2011. http://d-nb.info/1011441519/34.
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Cywiński, Łukasz. "Magnetization dynamics and spin diffusion in semiconductors and metals." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3259622.
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Thesis (Ph. D.)--University of California, San Diego, 2007.<br>Title from first page of PDF file (viewed June 21, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 175-186).
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Kneip, Martin [Verfasser]. "Magnetization Dynamics in Diluted Magnetic Semiconductor Heterostructures / Martin Kneip." München : GRIN Verlag, 2009. http://d-nb.info/1187730718/34.
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Morales, Marienette B. "Magnetization Dynamics and Interparticle Interactions in Ferrofluids and Nanostructures." Scholar Commons, 2009. http://scholarcommons.usf.edu/etd/3913.
Full textAbstract:
Nanoparticle assemblies are of current interest as they are used in a wide variety of industrial
and biomedical applications. This work presents two studies aimed at understanding
the magnetization dynamics and interparticle interactions in nanoparticle assemblies
and various types of ferrofluids.
First, we studied the influence of varying strengths of dipolar interaction on the static
and dynamic magnetic properties of surfactant-coated monodispersed manganese-zinc ferrite
nanoparticles using reversible transverse susceptibility. We tracked the evolution of
the anisotropy peaks with varying magnetic field, temperature, and interaction strength.
The anisotropy peaks of weakly interacting particles appears as non-symmetric peaks and
at lower fields in a unipolar transverse susceptibility scan. On the other hand, a strongly
interacting particle system exhibits symmetric anisotropy peaks situated at higher field
values.
In the second study, we successfully synthesized stable ferrofluids out of high quality
Fe
3O4 and CoFe2O4
nanoparticles. Such ferrofluids are excellent systems for the investigation
of physics of relaxation phenomena in magnetic nanoparticles. Motivated by the
need to understand their peculiar magnetic response, a comparative study on Fe
3O4
- and
CoFe
2O4
-based ferrofluids was performed. We investigated cases in which particle blocking
and carrier fluid freezing temperatures were close and far apart from each other. Our
experimental results reveal the true origin of the glass-like relaxation peaks that have been
widely observed in ferrofluids by many groups but remained largely unexplained. Contrary
to the speculation of previous literature, we argue that the formation of the magnetic
anomaly is due not only to the particle blocking but also to its correlation with the the
carrier fluid freezing effects. It is also shown that the nature of these peaks is strongly
affected by varying particle size and carrier fluid medium. Quantitative fits of the frequency
dependent AC susceptibility to the Vogel-Fulcher scaling law clearly indicate that
the blocking of magnetic nanoparticles in the frozen state significantly affects the interparticle
dipole-dipole interaction, causing characteristic spin-glass-like dynamics. A clear
correlation between the blocking and freezing temperatures emerges from our studies for
the first time.