Tesi sul tema "Aimantation en dynamique"
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Ouari, Bachir. "Dynamique de l'aimantation des particules superparamagnétique avec anisotropie triaxiale". Perpignan, 2006. http://www.theses.fr/2006PERP0739.
In this thesis, a theoretical study of the dynamics of the magnetization of superparamagnetic nanoparticles with triaxial (orthorhombic) anisotropy has been carried out using the Néel-Brown model. Numerical and analytical solutions of the Fokker-Planck equation given by Brown, which describes the relaxation of the magnetization in the nanoparticles, have been obtained in order to facilitate this study. The process of relaxation of the magnetization is characterized by the longest relaxation time, integral relaxation time, and, in the frequency domain, by the longitudinal and transverse components of the magnetic susceptibility tensor. The numerical solutions allows us to evaluate these characteristics for typical values of the dissipation constant α, temperature T, anisotropy constants with and without a uniform external magnetic field H0. By using the approach of Kramers-Brown-Coffey, analytical equations for the magnetization relaxation times and for the longitudinal and transversals components of the magnetic susceptibility have been deduced. These analytical equations are in complete agreement with the results of our numerical calculations. They have simple analytical forms and allow one to quantify the dependence of the relaxation times and the magnetic susceptibility on the temperature T, angular frequency , strength of the external field H, and dissipation constant α. Moreover they can be used to estimate the relaxation times and the magnetic susceptibility in wide ranges of variation of T,, H, and α. The results obtained may be considered as a complete solution of the problem of relaxation of the magnetization in nano particles with triaxial anisotropy
Deb, Marwan. "Spectroscopie magnéto-optique de grenat magnétique de bismuth fer : études statique et dynamique". Versailles-St Quentin en Yvelines, 2013. http://www.theses.fr/2013VERS0065.
The objective of this thesis is the extensive study of the magnetic, magneto-optical (MO) and electronic properties of the bismuth iron garnet (Bi3Fe5O12, BIG). BIG is a novel transparent magnetic material with exceptional MO properties. The first part of the thesis presents the studies of the static MO properties of BIG performed over a wide range of thickness (5nm-220nm) of photon energy (5nm-220nm) and of temperature (5K-740K). The obtained results have allowed understanding several intrinsic properties of this complex material such as its abnormal hysteresis loops and its electronic band structure. In the second part of the thesis, the optically induced magnetization dynamics has been studied. We have demonstrated that the excitation of BIG with linearly or circularly polarized femtosecond laser pulse triggers a coherent precession of the magnetization
Fessant, Alain. "Etude de la dynamique d'aimantation dans les couches minces magnétiques amorphes". Brest, 1991. http://www.theses.fr/1991BRES2028.
Venuat, Julien. "Etude statique et dynamique du renversement d'aimantation de petits objets d'anisotropie perpendiculaire". Université Louis Pasteur (Strasbourg) (1971-2008), 2006. https://publication-theses.unistra.fr/public/theses_doctorat/2006/VENUAT_Julien_2006.pdf.
This work deals with the study of the magnetization reversal of submicrometric dots with perpendicular anisotropy. The 1st part describes the fabrication of the dots (characteristic size between 200nm and 1μm) by e-beam lithography and ionic beam etching from continuous CoPt3 films and (CoxPt10Å)nx multilayers. Moreover, a magnetic field up to 1. 5T is applied via a micro-coil that is lithographied directly on the dots network. The study of the magnetic properties, described in the 2nd part of this manuscript, shows that the alloy films and the multilayers with tCo<0. 7nm present a perpendicular anisotropy. Magneto-optic experiments with Kerr effect prove that the coercivity of the dots increases when their size decreases. This tendency can be explained by the reversal mode that is dominated by the propagation of the domains walls, which is limited by the size of the dots. Finally, the 1st steps of the magnetization reversal of the dots under magnetic impulsions of few ns was observed by MFM experiments
Venuat, Julien Kappler Jean-Paul. "Etude statique et dynamique du renversement d'aimantation de petits objets d'anisotropie perpendiculaire". Strasbourg : Université Louis Pasteur, 2007. http://eprints-scd-ulp.u-strasbg.fr:8080/782/01/Venuat2006.pdf.
Franco, Galeano Andres Felipe. "Effets de couplage sur la dynamique de couches magnétiques". Perpignan, 2012. http://www.theses.fr/2012PERP1106.
Due to its potential applications in the industry of magnetic recording media and the rapidly developing field of spintronics, the physics of stacked magnetic nanostructures has attracted a growing interest from the scienfic community during the last decades. One of the underlying issues of the multilayered magnetic systems used concerns the origin and effect of interlayer coupling as it plays a crucial role in the optimization of the magnetization switching. Accordingly, we have devoted the large part of the present thesis work to the study of the effect of such a coupling by considering various types thereof, and the switching mechanisms and magnetization profile they entail. We believe that our work will contribute to further optimizing the physical properties of magnetic multilayers as promising candidates for efficient information storage on magnetic media such as the Magnetic Random Access Memory (MRAM)
Raquet, Bertrand. "Dynamique d'aimantation dans une couche ultramince ferromagnétique. Application au système or/cobalt/or". Toulouse, INSA, 1996. http://www.theses.fr/1996ISAT0043.
Zagdoud, Amani. "Dynamique d’aimantation des systèmes ferromagnétiques induite par des impulsions laser femtosecondes dans le domaine spectral infrarouge". Strasbourg, 2011. https://publication-theses.unistra.fr/restreint/theses_doctorat/2011/ZAGDOUD_Amani_2011.pdf.
The aim of the study is to show how the ultrafast demagnetization and the subsequent rapid re-magnetization occur when exciting a ferromagnetic material with low energy infrared pulses. Towards that goal, we have used mid-infrared femtosecond laser pulses (l = [3-10 µm]) to excite CoPt3, Ni and Co ferromagnetic thin films. The magneto-optical response is then probed in the visible (l = 798 nm). Our results show that even though only intraband transitions occur, the demagnetization process and its subsequent relaxation to the lattice and to the environnement are still the dominant processes involved in the magnetization dynamics. We also show that the material band structure is important to interpret the thermalization synamics of the spins that occur before the heating of the lattice. For specific experimental configurations, we show that it is possible to induce a motion of precession of the magnetization around the effectif magnetic field and observe it while it is damped. Such approach gives an accurate description of the precession dynamics that can be modelled with Landau-Lifschitz Gilbert equations. The magnetization dynamics induced at 6. 5 µm in nickel shows an oscillatory behaviour with a period of 2 ps. Those oscillations are indpendents from the external magnetic filed angle, the pump intensity and the film thickness. We attribute this result to the excitation of a two-magnons mode on the NiO by an acoustic mode generated in nickel
Spenato, David. "Dynamique de l'aimantation et distribution de l'anisotropie magnétique dans les couches minces ferromagnétiques douces amorphes : modélisation et étude expérimentale". Brest, 1994. http://www.theses.fr/1994BRES2025.
El, Mrabti Halim. "Dynamique de l’aimantation des nanoparticules magnétiques en présence d’un champ magnétique alternatif". Perpignan, 2012. http://www.theses.fr/2012PERP1082.
In the present work, the dynamics of the magnetization of single domain magnetic nanoparticles assisted by an external alternative current (ac) magnetic field of arbitrary strength and orientation, in presence of the thermal agitation, is treated in the context of the Brown’s model of coherent rotation of the magnetization. Our main objective was to treat nonlinear effects due to strong ac magnetic excitations in the dynamics of the magnetization of an individual nanoparticle and an assembly of non-interacting nanoparticles across a wide frequency range (up to 10 GHz). Our study has been focused on the nanoparticles both with a uniaxial and biaxial anisotropy. We have calculated the relevant physical quantities such as nonlinear dynamical susceptibility, magnetization reversal time, and dynamic magnetic hysteresis (DMH). The results show a strong dependence of nonlinear response and the DMH on the anisotropy constant, biaxiality constant, temperature, amplitudes and orientations of the dc and ac fields. Furthermore, in contrast to uniaxial particles, the nonlinear ac stationary response and DMH strongly depend on the azimuthal direction of the ac field and not only the polar angle between the easy axis and the external field vector. In the present work, we have developed a theoretical approach to treat the dynamics of the magnetization of the magnetic nanoparticles subjected to a strong ac field, opening a new way to the solution of other nonlinear problems
Moritz, Jérôme. "Enregistrement ultra-haute densité sur réseau de plots magnétiques nanométriques à aimantation perpendiculaire au plan". Grenoble 1, 2003. http://www.theses.fr/2003GRE10226.
Arrays of out-of-plane magnetized nano-dots have been realized in two different steps : nano-structuration of a Silicon substrate by e-beam lithography first, deposition of Co/Pt multilayers by magnetron sputtering second. Writing and reading tests achieved by using a quasi-static tester, on which commercial heads have been mounted, have shown the writability on these pre-patterned media, as well as the good, competitive and constant signal to noise ratio obtained for any bit length. High frequencies measurements have been carried out either and it can be concluded the data rates reach the GHz mark for this new storage technology. On a fundamental point of view, the thermal activation processes in out-plane-magnetized thin layers and their effects on the magnetization reversal and dynamics have been studied. It was been shown the activation law follows an inverse field dependence (droplet model), which leads to other stability criteria for the information retention
Rassam, Mhamed. "Dynamique du retournement de l'aimantation de nanoparticules magnétiques dans l'approche multi-spins". Perpignan, 2012. http://www.theses.fr/2012PERP1172.
In this work, we investigate the effect of a time-dependent microwave field on magnetization switching of a magnetic nanoparticle in atomic approach. The main objective is to establish conditions conducive to a reversal optimized in terms of power and static magnetic field. To achieve this, we proceed by two steps: first, we adopt a macroscopic approach and develop a general method to optimize a microwave field (direction, magnitude and frequency) to achieve the magnetization’s switch. In the second step, we take into account the effects of finite size and edge and study the effect of misalignment of the atomic spins on the reversal field. The results of this work are directly compared with experimental measurements on isolated nanoparticles and meet some of the goals of our ANR DYSC project
Hrabec, Ales. "Etude de la dynamique de l'aimantation dans des nanostructures magnétiques à aimantation perpendiculaire : effet du champ magnétique et du courant électrique". Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00767418.
Shihab, Sylvain. "Excitation et détection optiques de la dynamique de l’aimantation dans le semi-conducteur ferromagnétique (Ga,Mn)(As,P)". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066548/document.
Development of impulsional laser enhanced the study of the magnetization dynamic in the temporal domain (fs-ns) with optical techniques. In thin ferromagnetic films with a weak optical absorption, excitation and optical mechanisms are not yet fully understood. To increase our understanding, variations of magnetic parameters are required. To that end, the magnetic semiconductor like (Ga,Mn)(As,P) are a good choice due to their magnetic properties easily adjustable thanks to the coupling between magnetic and semiconductor properties. In this thesis, conditions for optimal excitations were established. Supposing a thermal excitation origin, we assessed the transient change of temperature and anisotropy constant. I also established the role of the optical absorption and dephasing due to the finite magnetic layer thickness in the spin-waves detection process. The observation of several spin-waves gave me the opportunity to assess the spin-stiffness constant as a function of phosphorus. On the contrary of theoretical prediction, I showed that the spin-stiffness hardly vary with the phosphorus concentration
Ghaddar, Abbas. "Dynamique de renversement de l’aimantation dans les nanofils ferromagnétiques". Brest, 2010. http://www.theses.fr/2010BRES2016.
Nanotechnology encompasses large number of scientific and technical areas with a common length of interest, the nanometer (a thousandth of a micron). Progress in the control of matter al the nanometer scale opens new opportunities, scientific challenge, technical and economic challenges in various economy sectors and at the crossing point of several fields. The study and use of reduced dimension (2D films, 1D wires and 0D grains) nanostructured materials generates substantial progress due to their unique properties compared to bulk materials (3D). The objective of this thesis is to correlate conditions of preparation, to structural and magnetic properties of materials through the study of nanowires made of nickel and cobalt. The first part of this work involves production of nanowires in polycarbonate membrane pores. Determination of growth conditions allowed us to obtain high quality nanowires. Analysis of the electroplating process led to the understanding of growth mechanisms pertaining to nanomaterials. Structural characterization and determination of the chemical composition of electrodeposited nanowires are also presented. In the second part, we study the magnetic properties of the nanowires. Magnetic characterisation is based on VSM magnetometry and FMR. The quasi-static study of magnetization reversal reveals the presence of several modes of magnetization reversal depending on the nanowire geometry. Dynamic (frequency) studies confirm our static (zero frequency) results and allow us to control the effective anisotropy field strength in nanowire arrays. FMR measurements at low temperature unveiled the presence f novel terms in addition b tire magnetic anisotropy of the sample. Our studies are interpreted using several theoretical models such as Stoner-Wohlfarth, “Curling”, “Preisach” and “Landau-Lifshitz-Cilbert”. Good agreement is obtained between theory and experiment in our work
Laire-Peirano, André de. "Quelques problèmes liés à la dynamique des équations de Gross-Pitaevskii et de Landau-Lifshitz". Paris 6, 2011. http://www.theses.fr/2011PA066513.
Piquerel, Raoul. "Retournement de l'aimantation assisté par un champ micro-onde d'une nanoparticule individuelle". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00767410.
Chaves, Dayane de Souza. "Dynamique de parois chirales dans les multicouches magnétiques avec anisotropie perpendiculaire". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY019/document.
The aim of this thesis has been to study domain wall dynamics in magnetic thin films with perpendicular magnetic anisotropy embedded in a non centrosymmetric stack. In this kind of system the competition between the symmetric Heisenberg exchange and an antisymmetric exchange term, called the interfacial Dzyaloshinskii-Moriya interaction (DMI), favours non collinear magnetic textures with a fixed chirality, like chiral Néel domain walls and skyrmions. In this work we have been interested in the field and current-driven dynamics of chiral Néel walls in trilayer stacks, typically consisting of a thin Co film deposited on Pt and capped with an oxide.We have shown that the statics and dynamics of a domain wall (DW) is strongly affected by the DMI. The DMI favours Néel internal structure (rather than the Bloch structure usually found in symmetric systems) with a fixed chirality. By comparing DWs in Pt/Co/Pt (no DMI) and Pt/Co/AlOx (strong DMI), we have shown that in the presence of DMI, DWs can be moved more efficiently by a magnetic field. The stabilization of the internal DW structure by the DMI allows the precessional regime to be pushed to large magnetic fields and large velocities to be reached.Opposite to what is predicted by 1D models we show that in the presence of DMI, the DW velocity saturates after the Walker field, and that the saturation velocity is proportional to the ratio of the DMI strength and the saturation magnetization (D/Ms). The enhancement of the saturation velocity in systems with reduced Ms is shown by comparing DW dynamics in Pt/Co/GdOx and Pt/Co/Gd stacks. This also means that, knowing Ms, measuring the DW saturation velocity provides an original method to quantify the interfacial Dzyaloshinskii-Moriya interaction, as we show in this work.This method has been used to measure the DMI interaction in Pt/Co/AlOx trilayers in which the top Co interface presents a varying degree of oxidation. We show that besides the strong DMI at the Pt/Co interface, the Co/oxide interface also provides a DMI contribution of the same sign, whose strength depends on the degree of oxidation of the Co/AlOx interface. We also observe that this DMI scales with the perpendicular magnetic anisotropy, which suggest a common origin for the two effects. Finally we have shown preliminary results of field- and current-driven dynamics of DWs in a ferrimagnetic system (GdCo). While close to the compensation composition domain walls in Pt/GdCo/Ta trilayers can be moved to high velocities only by very high magnetic fields, the current driven dynamics is very efficient and depinning currents low. This effect is attributed to the 1/ Ms dependence of the spin-orbit torque acting on the DW magnetization
Houssameddine, Dimitri. "Dynamique de l'aimantation de nano-oscillateurs micro-ondes à transfert de spin". Phd thesis, Université Joseph Fourier (Grenoble), 2009. http://tel.archives-ouvertes.fr/tel-00466637.
Bianchini, Laurence. "Dynamique hyperfréquence d'aimantation induite par transfert de spin". Phd thesis, Université Paris Sud - Paris XI, 2010. http://tel.archives-ouvertes.fr/tel-00846804.
Shihab, Sylvain. "Excitation et détection optiques de la dynamique de l’aimantation dans le semi-conducteur ferromagnétique (Ga,Mn)(As,P)". Electronic Thesis or Diss., Paris 6, 2015. http://www.theses.fr/2015PA066548.
Development of impulsional laser enhanced the study of the magnetization dynamic in the temporal domain (fs-ns) with optical techniques. In thin ferromagnetic films with a weak optical absorption, excitation and optical mechanisms are not yet fully understood. To increase our understanding, variations of magnetic parameters are required. To that end, the magnetic semiconductor like (Ga,Mn)(As,P) are a good choice due to their magnetic properties easily adjustable thanks to the coupling between magnetic and semiconductor properties. In this thesis, conditions for optimal excitations were established. Supposing a thermal excitation origin, we assessed the transient change of temperature and anisotropy constant. I also established the role of the optical absorption and dephasing due to the finite magnetic layer thickness in the spin-waves detection process. The observation of several spin-waves gave me the opportunity to assess the spin-stiffness constant as a function of phosphorus. On the contrary of theoretical prediction, I showed that the spin-stiffness hardly vary with the phosphorus concentration
Houssameddine, Dimitri. "Dynamique de l'aimantation de nano-oscillateurs micro-ondes à transfert de spin". Phd thesis, Grenoble 1, 2009. http://www.theses.fr/2009GRE10137.
This thesis addresses a current topie of spinelectronics which are steady-state oscillations of the magnetization induced by spin transfer torque. Ln magneticl nanostructures, the large oscillation amplitude is of interest since it allows probing of the magnetization dynamics in the non-linear regime but also fo~ integrated microwave components. Here the small size of the devices and the relatively large frequency tuning range are promising properties for futurel telecommunications. However, before integration major issues need to be addressed such as increasing the output power and understanding the spectral purity. Therefore, we studied experimentally the dynamic behaviour of two types of spin transfer oscillators. The fll"st type focuses on a spin valve structure with a perpendicularly magnetized polarizing layer. We show that large amplitude magnetization oscillations around its energy maximum can be established as a resuh of the perpendicular polarizer. With the help of micromagnetic simulations, we were able to interpret qualitatively the experimental resuhs. The second type of structures are MgO based magnetic tunnel junction oscillators of large output power. We developed an experimental set-up to follow the magnetization dynamics in the time domain as well as a data processing protocol to analyze the spectral purity. We identified different transient processes limiting the coherence of the magnetic oscillations, in particular frequency fluctuations on tens of nanoseconds time-scale
Gorchon, Jon. "Current and field induced magnetization reversal in Pt/Co/Pt and (Ga, Mn)(As, P) ferromagnetic films". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112143.
Effectively manipulating the magnetic state of a ferromagnet has a great interest for possible technological applications. Understanding the underlying fundamental mechanisms is thus particularly important. In some cases, the understanding of some mechanisms may even importantly impact other areas of physics. This is the case for example with field induced magnetic domain walls motion in the creep regime, where the wall can be assimilated to an elastic interface and follows an universal behavior. This thesis presents through an experimental work on Pt/Co/Pt ultra-thin samples, a complete description of the temperature and field dependent domain wall dynamics. A self-consistent analysis allows the extraction of all control parameters, identifying the new Thermally Activated Flux Flow regime, and confirming universal thermal scaling exponents. A second study focuses on current induced domain wall motion in an extended geometry of a (Ga,Mn)(As,P) ferromagnetic film. This study unveils domain wall shape instabilities under a gradient of current. The instability limits are analytically predicted in agreement with the experimental observations. A third work concerns the magnetization reversal mechanism evidenced at the interface between a (Ga,Mn)(As,P) film and a non-ferromagnetic electrode under a current flow. The reversal is shown to be stochastic and mainly governed by the spin accumulation at the interface, which reduces importantly the local magnetization. A simplified model allows the description of the reversal probability and the time scales involved in the mechanism of reversal are accessed and discussed
Camilleri, Christophe. "Etude de la dynamique de spin des porteurs et des ions Mn2+ par des expériences d'effet Kerr magnéto-optique résolu en temps de type pompe-sonde sur des puits quantiques semimagnétiques de Cd1-xMnxTe de type p et n". Montpellier 2, 2000. http://www.theses.fr/2000MON20119.
Ciornei, Mihaela-Cristina. "Rôle de l'inertie dans la dynamique dissipative du macrospin". Phd thesis, Ecole Polytechnique X, 2010. http://tel.archives-ouvertes.fr/tel-00460905.
Nguyen, Van Dai. "Magnétorésistance de magnon reversement de l'aimantation et dynamique de parois dans FePt et NiFe nanostructures". Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENY039/document.
In the first part of this thesis, we study the magnetization reversal process of FePt nanowires with high magnetocrystalline anisotropy. When reducing the wire width below the mean dendrite width, the magnetization reversal favors a transition from the dendrite growth to the propagation of a single domain wall (DW). Further decreasing of the width towards the disorder length and/or the mean edge roughness leads to a large increase of coercivity, which finally results in a mix of DW propagation and nucleation in ultra-narrow wires. The second part focuses on the use of Magnon magnetoresistance (MMR), i.e., the magnon contribution to the resistivity, to study the magnetization reversal in nanostructures with either perpendicular (FePt) or planar magnetization (NiFe). We showed that MMR can be used in nanowires and nanomagnets, in particular to detect DW position in nanowires processed in a single layer. Finally, the dynamic of DW depinning under field and current in both FePt and NiFe systems has been studied. We observe three different modes of DW depinning, which depend on the nature of defects, or on the geometry of the constriction. Statistical analysis of the pinning time indeed shows that the depinning path can be described as simple path, serial paths or alternative paths. Additionally, the effect of DC current on all depinning mechanisms is found to be equivalent to the effect of applied field which, allow measuring the spin transfer efficiency in these systems
Klughertz, Guillaume. "Dynamique d'aimantation ultra-rapide de nanoparticules magnétiques". Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE004/document.
The goal of this thesis is to explore analytically and numerically the magnetization dynamics in magnetic nanoparticles. Firstly, we study the Néel dynamics of fixed. We show that one can efficiently control the magnetization reversal of a nanoparticle by using a chirped excitation (autoresonance). This study reveals that the Gilbert damping and the temperature alter the efficiency of the reversal, while dipolar interactions can improve it. The stationary properties of a monolayer of nanoparticles are then examined by computing ZFC curves with a Monte Carlo method. We observe that structural disorder has no effect on the blocking temperature. Finally, we investigate the behavior of an ensemble of interacting nanoparticles moving in a fluid with a molecular dynamics approach. Our numerical simulations reproduce the usual chain and ring-like equilibrium configurations. We then study the dynamics of these structures and show the existence of super-spin waves
Balestrière, Pierrick. "Dynamique de l'aimantation assistée par un champ électrique dans des dispositifs à base de (Ga,Mn)As". Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00568896.
Rakii, Abdelmoula. "Films minces amorphes de CoZr et CoZrRe superdoux et d'aimantation élevée : élaboration par pulvérisation cathodique et étude magnétique statique et dynamique". Grenoble 1, 1992. http://www.theses.fr/1992GRE10083.
EL, HARFAOUI MOHAMMED. "Etude de l'etat magnetique localement cante et de sa dynamique dans le ferrite de lithium-titane dilue". Paris 6, 1988. http://www.theses.fr/1988PA066650.
Berthelot, Christel. "Modélisation de la dynamique d'aimantation par effet de transfert de spin dans des vannes de spin de taille nanométrique". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0076/document.
Ever since its prediction, spin transfer has spawned a lot of interest, and some applications have already been commercialized. However the spin transfer effect is still not fully understood. This thesis focused on magnetization dynamics and spin transfer effect in spin valves with out of plane magnetization, proven to be more efficient. With this in mind, we developped a software simulating magnetization dynamics in spin valve. We then confronted the software with experimental results to check our model and its hypotheses veracity. Another part of this thesis was to study current-field state diagrams, which offer a global perspective on magnetization behavior. We managed to show the applied field and the anisotropy could produce a symmetry breaking of the system and thus explain the experimental results. We were also able to highlight canted states of the magnetization. Those are frozen states of the magnetization for certain angles. The last part describes magnetization dynamics at different time scales from a second to a hundred picoseconds. We showed the macrospin model is not appropriate for short current pulses, although we could highlight the influence of some parameters. We finally the micromagnetics model allowed for a better description of the experimental results
Brinis, Drifa. "Dynamique d'aimantation dans les assemblées d'agrégats ferromagnétiques : effets des interactions". Thesis, Normandie, 2017. http://www.theses.fr/2017NORMR049/document.
In our work, we used Monte Carlo technique to simulate the effect of dipolar interactions on the magnetization reversal of a ferromagnetic nanoparticles assembly. In our model, we considered nanoparticles with uniaxial anisotropy and specifically the Cobalt. With the condition KV/kBT >> 1, the magnetic moment of each nanoparticle is fixed in its equilibrium positions and it can not fluctuate around. We chose to our investigation the ac susceptibility because it provides the advantage of making the study with a wide frequency range without changing measurement technique, because the measurement time is equal to the inverse of the frequency of the alternating magnetic field applied. We studied twelve types of assemblies each one differs from the other by some properties : The shape of the assembly, the spatial distribution of the nanoparticles or the distribution of the anisotropy axes. And we discerned the influence of each of theses parameters on the effect of dipolar interactions on the magnetization reversal
Domingues, de Sousa Flávia. "Study and modeling of a Fe-Cr-Co magnet based Variable Flux Memory Machine for its supply and mechanical sensorless control at high speed". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0105.
Permanent Magnet Synchronous Machines (PMSMs) have been widely used for electrification transportation applications. Producing their magnet flux from rare-earth magnets (e.g. Nd-Fe-B magnets), these machines have had their long-term use increasingly questioned due to the risks of supply, price variability and the environmental challenges related to the extraction and recycling of these mentioned materials. To this scenario, can be also added the limitations of PMSMs for being used in large torque-speed ranges, requiring usually the implementation of flux-weakening strategies, based on supplying the machine with an increasingly negative direct stator current component as the rotor speed also increases. In case of non-salient pole machines the Joule losses can be enhanced and the efficiency consequently reduced. Capable of operating in a wide torque-speed range, the Variable Flux Memory Machines (VFMMs) have emerged as an option characterized by controllable magnetic flux density from short-time currents pulses supplying the armature windings. All this thanks to the highly non-linear hysteresis loop characterizing the low coercive force magnets used as source of flux. Al-Ni-Co alloys has been the choice of many researches for these applications. However, similar magnetic materials as Fe-Cr-Co are still little explored, besides advantageous characteristics as their lower content of Cobalt and mechanical proprieties. Within this framework, this thesis proposes the study of single-type AC-magnetized single pole pair VFMM, composed of a Fe-Cr-Co-based rotor. The machine geometry is designed from a PMSM, in which the rotor pf Nd-Fe-B is directly replaced by a solid cylinder of FeCrCo36/5. First, a focus on the study of the magnetic behavior of the magnet when inserted in the machine environment. Because of the anisotropy differentiating the hysteresis loop of the FeCrCo36/5 in the a easy or hard magnetization directions, two different methodologies are proposed for describing the partial magnetization profile via experimental tests at standstill and Finite Element Analysis simulations. The achieved results are compared with the reference obtained from an ideal measuring equipment (HysteresisGraph). The effects of a stator saturation and geometry as also the anisotropy shape are explored for justifying the differences observed. A following study focused on the magnetization under operation and the torque control is developed considering the an adapted sensorless algorithm. In this context, the present research proposes the use of a Proportional Integral Phase Locked-Loop for estimating the rotor position and speed. An attention is given to the offset angle compensation required for adjusting the mentioned position according to the acquisition system (active filters) and the characteristics of the estimation method used. A parametric sensitivity study allows the identification of the dq-axis inductances as the most critical parameters to an accurate correction angle estimation. For this reason, this research thesis is also interested in proposing a methodology to describe the d- and q-axis inductances from FEA simulations performed by considering the anisotropy effects of the magnet and also the saturation of the stator material. A variable reluctance is identified in the machine and its effect on the correction angle is studied
Rouabhi, Mokhtar. "Mécanismes d'aimantation et dynamique des parois dans des films minces magnétiques amorphes de CoNbZr". Rouen, 1993. http://www.theses.fr/1993ROUES034.
Guillemard, Charles. "Half-metal magnets Heusler compounds for spintronics". Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0110.
Improvements in thin film elaboration methods and a deeper understanding of condensed matter physics have led to new exciting phenomena in spin electronics (spintronics). In particular, magnetization reversal by spin-orbit and spin-transfer torque as well as the development of spin waves based devices have placed the Gilbert magnetic damping coefficient as a key parameter for future data storage and information processing technologies. The prediction of ultralow magnetic damping in Co2MnZ Heusler half-metal magnets is explored in this study and the damping response is shown to be linked to the underlying electronic structure. By substitution of the Z element in high quality Co2MnZ (Z=Al, Si, Ga, Ge, Sn and Sb) epitaxial thin films grown by molecular beam epitaxy, electronic properties such as the minority-spin band gap, Fermi energy position in the band gap, and spin polarization can be tuned and the consequences for magnetization dynamics analyzed. Experimental results allow us to directly explore the interplay of spin polarization, spin gap and Fermi energy position, with the magnetic damping obtained in these films (together with predictions from ab initio calculations). The ultralow magnetic damping coefficients measured in the range from 4.1 x10-4 to 9 x10-4 for Co2MnSi, Co2MnGe, Co2MnSn and Co2MnSb are the lowest values ever reported in conductive layers and offer a clear experimental demonstration of theoretical predictions on half metal magnetic Heusler compounds. Then, the relation between the Gilbert damping and the ultrafast demagnetization time in quaternary Co2MnSixAl1-x compounds with a tunable spin polarization is analyzed. This way, it is possible to confront theoretical models unifying those two quantities that live in different timescales. Finally, structural and magnetic properties of Mn3Ga/Co2YZ Heusler superlattices are investigated in order to combine ultralow Gilbert damping coefficient, minority spin band gap and perpendicularly magnetized heterostructures, another requirement for low energy consumption devices. Through the present work, we aim to prove that Heusler compounds provide an excellent playground to study fundamental magnetism and offer a pathway for future materials design
Ferté, Tom. "Dynamique ultrarapide de l'aimantation dans les alliages de métaux de transitions et de terres rares". Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE018/document.
My PhD work describes the pico and femtosecond magnetization dynamics using the time structure of X-rays. I studied the ultrafast demagnetization of thin films (~ 20 nm) for various transitions metals (TM) - rare earths (RE) alloys. My studies have been performed by using two experimental techniques which are sensitive to the magnetization and which are time resolved: tr-XMCD and tr-MCDAD. These two experimental techniques also show chemical selectivity allowing to distinguish the TM and RE dynamics. They are both based on pump-probe experiments which were used at the SOLEIL and BESSY II synchrotrons
Clédière, Jessy. "Simulation des processus d'aimantation dans des matériaux à anisotropie aléatoire et propriétés dynamiques d'aimantation dans des rubans nanocristallins doux". Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10085.
Shokeen, Vishal. "Ultrafast magnetization dynamics in ferromagnetic transition metals : a study of spins thermalization induced by femtosecond optical pulses and of coupled oscillators excited by picosecond acoustic pulses". Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE035.
In this thesis, we have investigated the magnetization dynamics at picosecond and femtosecond time scale using time resolved magneto-optical pump probe technique. At picosecond time scale, the magnetization precession is induced by ultrafast acoustic pulses in a three layered structure with two ferromagnetic layers separated by varying thickness of metallic spacer layer (Ni/Au/Py). The magnetization precession dynamics of the Ni layer is modified due to the interlayer exchange interaction with the Py layer and the synchronized precession of the coupied ferromagnetic layers has been observed. At the timescale of 50fs, coherent magneto-optical, non-thermal, thermal and relaxation dynamics of charges and spins in ferromagnetic transition metals (Ni, Co and Fe) is studied by using 11fs optical pulses in a very low perturbation regime. The spin orbit interaction and exchange interaction play a significant role in the demagnetization of the ferromagnetic metals induced by femtosecond pulses
Grolier, Valérie. "Propriétés magnétiques statiques et dynamiques des couches ultra-minces co/au : étude magnéto-optique". Paris 11, 1994. http://www.theses.fr/1994PA112095.
Fan, Xiaofei. "Contrôle ultrarapide de l'aimantation dans des hétérostructures à base de VO₂". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0271.
(1) We have investigated the phase transition in ultrathin amorphous VO₂ and its physical mechanism: We have successfully prepared ultrathin (nano-scale) amorphous VO₂ films with significant phase transition by magnetron sputtering and demonstrated the phase transition of amorphous VO₂ - EGT. In addition, we quantitatively modeled the phase transition of amorphous VO₂ and classified different thicknesses of VO₂ into "strong system" (>5 nm) and "fragile system" (0-2 nm). For the strong system, the material properties are less affected by temperature, and the Arrhenius model is used to describe the electron transport of VO₂ phase transition. While for the fragile system, the material properties are more affected by temperature fluctuations, and the Vogel-Tammann-Fulcher model can be used for analysis. The results demonstrate the phase transition mechanism of amorphous materials and provide a new idea for understanding phase transition. In addition, this direct method of growing ultrathin VO₂ using magnetron sputtering is convenient and fast, and it can be grown in the same batch with other materials within the heterostructure, which is expected to promote the application of phase transition materials in practical devices.(2) We explored a method to dynamically regulate the interlayer exchange coupling by phase transition: we introduced the VO₂ into the ferromagnetic/nonmagneticspacer/ferromagnetic heterostructure, and successfully realized the reversible transformation of the antiferromagnetic coupling and ferromagnetic coupling through regulating conduction electrons by MIT of VO₂. At the same time, from the analysis of the change of magnetic properties, we clarify that the IEC induced by VO₂ in different electronic states is dominated by the RKKY and spin dependent tunneling. Furthermore, we fully investigate the physical root behind the regulation of IEC by the VO₂, and reveal the regulation mechanism of the interface spin effect by the regulation of electronic states of non-magnetic spacer. This part of the work proposes a novel approach to the dynamic regulation of IEC, which provides new ideas for the application of IEC in spintronic devices.(3) We study the dynamic regulation of spin-polarized hot electron transport by phase transition: In a ferrimagnetic/nonmagnetic diffusion channel/ferromagnetic heterostructure, we introduce VO₂ into the diffusion channel to control the electrical properties of the channel by MIT, and then dynamically regulate the transport of spin-polarized hot electrons generated by the ultrafast demagnetization of GdCo. By regulating the on/off of hot electrons in the channel, we achieve dynamic regulation of the magnetization of adjacent ferromagnetic layers. Meanwhile, with the optical property changes introduced by VO₂, we have successfully achieved the switching of the magnetization of ferromagnetic materials without AOS in ferrimagnetism excited by a single-pulse femtosecond laser. Furthermore, we have verified and analyzed the mechanism of this ultrafast modulation. In this work, we use the phase transition material VO₂ as a diffusion channel with controllable electrical properties to control the hot electron transport through MIT. The results show that the non-magnetic materials play an important role in various types of heterostructures
Grassi, Matías Pablo. "Spin waves in inhomogeneous magnetization distributions". Thesis, Strasbourg, 2021. http://www.theses.fr/2021STRAE014.
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
Besbas, Jean. "Influence de la densité de trous sur la dynamique des charges et de l'aimantation du (Ga, Mn)As en couche". Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00798208.
Guillemard, Charles. "Half-metal magnets Heusler compounds for spintronics". Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0110.
Improvements in thin film elaboration methods and a deeper understanding of condensed matter physics have led to new exciting phenomena in spin electronics (spintronics). In particular, magnetization reversal by spin-orbit and spin-transfer torque as well as the development of spin waves based devices have placed the Gilbert magnetic damping coefficient as a key parameter for future data storage and information processing technologies. The prediction of ultralow magnetic damping in Co2MnZ Heusler half-metal magnets is explored in this study and the damping response is shown to be linked to the underlying electronic structure. By substitution of the Z element in high quality Co2MnZ (Z=Al, Si, Ga, Ge, Sn and Sb) epitaxial thin films grown by molecular beam epitaxy, electronic properties such as the minority-spin band gap, Fermi energy position in the band gap, and spin polarization can be tuned and the consequences for magnetization dynamics analyzed. Experimental results allow us to directly explore the interplay of spin polarization, spin gap and Fermi energy position, with the magnetic damping obtained in these films (together with predictions from ab initio calculations). The ultralow magnetic damping coefficients measured in the range from 4.1 x10-4 to 9 x10-4 for Co2MnSi, Co2MnGe, Co2MnSn and Co2MnSb are the lowest values ever reported in conductive layers and offer a clear experimental demonstration of theoretical predictions on half metal magnetic Heusler compounds. Then, the relation between the Gilbert damping and the ultrafast demagnetization time in quaternary Co2MnSixAl1-x compounds with a tunable spin polarization is analyzed. This way, it is possible to confront theoretical models unifying those two quantities that live in different timescales. Finally, structural and magnetic properties of Mn3Ga/Co2YZ Heusler superlattices are investigated in order to combine ultralow Gilbert damping coefficient, minority spin band gap and perpendicularly magnetized heterostructures, another requirement for low energy consumption devices. Through the present work, we aim to prove that Heusler compounds provide an excellent playground to study fundamental magnetism and offer a pathway for future materials design
Hinschberger, Yannick. "Etude théorique des effets relativistes induits par une impulsion lumineuse ultra-rapide dans la matière". Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00923154.
Haidar, Mohammad. "Role of surfaces in magnetization dynamics and spin polarized transport : a spin wave study". Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00869643.
Pouget, Stéphanie. "Contribution à l'étude de l'influence de la dilution sur les propriétés magnétiques de composés isolants frustrés". Toulouse, INSA, 1993. http://www.theses.fr/1993ISAT0039.
Tranchida, Julien. "Multiscale description of dynamical processes in magnetic media : from atomistic models to mesoscopic stochastic processes". Thesis, Tours, 2016. http://www.theses.fr/2016TOUR4027/document.
Detailed magnetic properties of solids can be regarded as the result of the interaction between three subsystems: the effective spins, that will be our focus in this thesis, the electrons and the crystalline lattice. These three subsystems exchange energy, in many ways, in particular, through relaxation processes. The nature of these processes remains extremely hard to understand, and even harder to simulate. A practical approach, for performing such simulations, involves adapting the description of random processes by Langevin to the collective dynamics of the spins, usually called the magnetization dynamics. It consists in describing the, complicated, interactions between the subsystems, by the effective interactions of the subsystem of interest, the spins, and a thermal bath, whose probability density is only of relevance. This approach allows us to interpret the results of atomistic spin dynamics simulations in appropriate macroscopic terms. After presenting the numerical implementation of this methodology, a typical study of a magnetic device based on superparamagnetic iron monolayers is presented, as an example. The results are compared to experimental data and allow us to validate the atomistic spin dynamics simulations
Callahan, Michael. "Analyse de la cinétique de transformation et des instabilités de déformation dans des aciers TRIP "Moyen Manganèse" de 3ème génération". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC065/document.
This thesis studies the mechanical behavior of a 0.2C-5Mn-2.5Al Medium Mn steel that exhibits a very high degree of work hardening due to transformation-induced plasticity (TRIP) during plastic deformation. During TRIP, paramagnetic retained austenite is transformed to ferromagnetic martensite with the application of plastic strain and generates a significant amount of work hardening. The rate of work hardening is seen to vary greatly depending on processing parameters—notably the intercritical annealing temperature. These steels also often deform heterogeneously through the propagation of Lüders or PLC strain bands.This research develops a method to characterize the kinetics of the TRIP effect through measurements of the samples magnetic properties. The method is novel in that it is performed in-situ with no effect on the tensile test and is able to correct for the effects of the applied stress on the magnetic properties. The results of these experiments were compared to characterizations of the strain bands to demonstrate that TRIP coincides with the passage of a Lüders or PLC band. The strain rate sensitivity of the steels is analyzed and the presence and type of PLC bands are characterized with respect to the transformation kinetics