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Les effets de transfert de spin sont devenus un sujet de recherche majeur ces quinze dernières années. Cependant, un manque de vérifications expérimentales pour beaucoup de modèles décrivant les effets de transfert de spin peut être constaté. Ceci est surtout lié à un manque de systèmes magnétiques modèles permettant un contrôle précis des paramètres pertinents utilisés dans les modèles théoriques. Dans ce travail deux systèmes magnétiques à aimantation perpendiculaire ont été analysés : les alliages amorphes de Co1-xTbx élaborés par pulvérisation cathodique et les super-réseaux [Co/Ni](111) élaborés par épitaxie par jets moléculaires. L'anisotropie et l'aimantation, qui sont des paramètres pertinents dans beaucoup de modèles sur le transfert de spin, sont variables dans une large gamme. L'origine de cette anisotropie est discutée. La structure des domaines magnétiques est analysée et les résultats des mesures de transport sont interprétés. Pour les super-réseaux [Co/Ni](111) une forte polarisation en spin au niveau de Fermi est démontrée grâce à des expériences de photo émission résolue en spin et un coefficient d'amortissement intrinsèque [alpha] très faible est trouvé. Il est conclu que les alliages amorphes de Co1-xTbx et les super-réseaux [Co/Ni](111) sont des systèmes modèles pour le transfert de spin. / Spin transfer torque effects have become a research subject of high interest during the last 15 years. However, in order to probe the fundamental physics of spin transfer torque model systems are needed. For a model system it must be as simple as possible to tune the significant parameters (magnetic and structural). In this work we analyze the suitability of two materials for this need. The studied materials are amorphous Co1-xTbx alloys elaborated by sputtering and MBE grown [Co/Ni](111) superlattices. Both systems show perpendicular magnetic anisotropy (PMA), which provides a uniaxial anisotropy to the system. This anisotropy and the magnetization, which are significant parameters for many models on spin transfer torque, can be tuned in a large range of values. The origin of this PMA is discussed. The domain structure is analyzed and transport measurements are interpreted. In addition we show a strong spin polarization of the electrons close to the Fermi level by doing photoemission experiments. A small intrinsic Gilbert damping parameter [alpha] is found by FMR spectroscopy. We conclude that both materials are good candidates to be used as model systems for spin transfer torque

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In the foundation of this work is the issue for production of non-magnetic materials with predetermined weak magnetic properties. Preferable solution is to dope these materials with ferromagnetic impurities in low concentrations. One of the efficient ways to obtain such materials is the use of powder metallurgy which gives an opportunity to produce complex powder compositions with variety of components in precisely specified concentrations.

The main objective of this thesis was to bring the first experimental evidence about the spin-Hall magnetoresistance (SMR) in the Terahertz (THz) spectral range. The time-domain THz spectroscopy (TDTS) was chosen as the main method, and we presented a new experimental scheme, which allows us to observe SMR or magnetoresistive effects with similar symmetry at a wide range of THz frequencies very efficiently. We focused on the study of SMR in the bilayers consisting of either a prototypical ferrimagnetic isolator or of heavy metal (FI/HM) and metallic stacks of ferromagnetic CoFeB and heavy metal Pt layer (FM/HM). While SMR shows a rapid decrease already at the lowest THz frequencies (< 1 THz) in the FI/HM structures, the SMR in FM/HM bilayers persists above 30 THz. These observations are then explained by a different mechanism of SMR. The second part of the thesis is devoted to the construction of the new TDTS setup and an easy-to-use model of the THz setup using the Gaussian description of THz radiation. The simulated results have been compared to corresponding experimental measurements using a spintronic THz emitter (STE). The last part of the thesis describes the emission of intensive THz pulses from large-area STE.

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<p>Predicting core losses in electromagnetic and electromechanical devices such as electric machines is crucial to avoid overheating or oversizing. This work focuses on predicting core loss under a dc bias condition which results in hysteresis loop distortion and an increase in the core loss. The interest in dc biased materials is to facilitate design of electric drive systems wherein the electric machine core is subject to a dc bias such as in homopolar machines. Owing to their simplicity and ease of use, Steinmetz-based models are considered in this work. Herein, four models based on Steinmetz Equations are studied and compared for dc offset sinusoidal field intensity waveforms. The model parameters are then characterized for a sample of M15 steel. Finally, the four models are compared with regards to their accuracy and performance under saturated conditions.</p>

No description available.

The development of Magnaquench in 1985 by the Delco-Remy laboratories, increased the research of applications of permanent magnets for use in automobiles. However the application of permanent magnet machines for cranking purposes has not been investigated much. Difficult operating conditions, like, a maximum current density of 35A/mm², and the ability to withstand demagnetizing armature currents up to 250% of the stall current require a new design approach to be developed. Commutation in the permanent magnet machine is obtained by a three phase full wave inverter. The machine - inverter model was simulated by a standard method (SPICE), and an second analytical method we developed. A permanent magnet brushless motor and a drive for cranking purposes is designed and simulated as a part of this thesis. / Master of Science

Additive manufacturing (AM) procedures involving the fusion of metal powders or wires tend to produce textured columnar grains, which can have positive effects on the magnetic performance of Fe-Si electrical steels in soft magnetic applications. This work focuses on understanding the impact of energy density (fluence) evolution of grain morphology and texture in Fe-3.8wt%Si and Fe-6wt%Si alloys produced by fusion-based AM. The results show that the development of texture in these alloys is promising for transformers and motor core applications. The desired texture observed in these alloys is obtained in one step unlike conventional manufacturing techniques. The alloys with higher energy fluence exhibited columnar grains with preferential growth orientation along <001> along the build axis, while those with lower energy fluences showed growth orientation in <111> direction. Further, the presence of ordered B2, D03 phases observed in AM processed Fe-6wt%Si improved the overall magnetic performance of these alloys. Additionally, due to relatively high saturation magnetization and sustainability at high operating temperatures, Fe-Co-2V (Hiperco) is an attractive alternative for soft magnetic applications. In this study, Fe-Co-2V alloy is successfully manufactured using fusion based AM techniques and was found to exhibit equiaxed grains in the AM processed conditions. The microstructure was found to have a significant influence on the magnetic properties, leading to intriguing microstructure-property connections. This study will cover these links between microstructure and properties as well as how energy density (fluence) affects the microstructure of the two potential Fe-Si and Fe-Co-2V soft magnetic systems.