Magnetic ageing investigation of bulk low-carbon silicon steel

In this paper, the magnetic ageing of a bulk forged non-annealed magnetic core, used in claw pole synchronous machine, is investigated. The study is carried out by characterizing the material properties of two groups of samples subjected to a thermal ageing at 180 °C that corresponds to the maximum operating temperature of the claw pole rotor. The investigated characteristics are the electrical conductivity, the magnetic properties, the material microstructure and the Vickers hardness. They were characterized along with the ageing time. The results show that, during the thermal ageing, the hysteresis losses and the Vickers hardness have been affected by the magnetic ageing, whereas the electric conductivity and the normal B-H curve have not been modified. The microstructure analyses showed that carbides precipitates were the main cause behind the magnetic ageing. Moreover, the comparison between the results of two groups of samples revealed the possibility that the magnetic ageing of the material could have started during the manufacturing process of the magnetic core

Magneto-thermal characterization of bulk forged magnetic steel used in claw pole machine

During the operation of Claw Pole (CP) machines, and for some operating loads, the magnetic core temperature can reach 180°C in some hot spots. As a consequence, the core electromagnetic properties may considerably change, impacting the machine performances. In such a case, a deep knowledge of the electromagnetic behavior as a function of the temperature is required. In this paper, we present a dedicated study of the CP rotor made from a forged magnetic steel. In fact, the CP magnetic properties heterogeneity and the claw shape made it necessary to extract specific samples that are characterized with a miniaturized Single Sheet Tester (SST). To that end, this work proposes a specific methodology to characterize the electromagnetic properties of the CP rotor material as a function of the temperature in order to better predict the machine electrical performances, especially regarding the iron losses

Excitation et détection optiques de la dynamique de l’aimantation dans le semi-conducteur ferromagnétique (Ga,Mn)(As,P)

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.Le développement des lasers impulsionnels a permis l’émergence de l’étude de la dynamique de l’aimantation dans le domaine temporel (fs-ns) par des techniques optiques. Dans les couches minces ferromagnétiques présentant une faible absorption optique les mécanismes de couplage de la lumière avec les propriétés magnétiques permettant l’excitation de la précession de l’aimantation et sa détection ne sont qu’imparfaitement connus. Pour développer leur compréhension il est nécessaire de faire varier les paramètres magnétiques. Les alliages semi-conducteurs ferromagnétiques sont pour cela des matériaux de choix du fait de leurs propriétés magnétiques aisément ajustables grâce au couplage entre les propriétés semi-conductrices et magnétiques. Les conditions pour une excitation optimale ont été précisées. L’excitation par une variation thermique transitoire des constantes d’anisotropie a été quantifiée. Le rôle de l’absorption et du déphasage optique dans la détection a été établi. L’observation de plusieurs ondes de spin a permis la détermination de la constante d’échange en fonction de la concentration en phosphore. J’ai montré que celle-ci variait peu, contrairement aux prédictions théoriques

Excitation and detection optical processes of the magnetization dynamic in the diluted magnetic-semiconductor (Ga,Mn)(As,P)

Le développement des lasers impulsionnels a permis l’émergence de l’étude de la dynamique de l’aimantation dans le domaine temporel (fs-ns) par des techniques optiques. Dans les couches minces ferromagnétiques présentant une faible absorption optique les mécanismes de couplage de la lumière avec les propriétés magnétiques permettant l’excitation de la précession de l’aimantation et sa détection ne sont qu’imparfaitement connus. Pour développer leur compréhension il est nécessaire de faire varier les paramètres magnétiques. Les alliages semi-conducteurs ferromagnétiques sont pour cela des matériaux de choix du fait de leurs propriétés magnétiques aisément ajustables grâce au couplage entre les propriétés semi-conductrices et magnétiques. Les conditions pour une excitation optimale ont été précisées. L’excitation par une variation thermique transitoire des constantes d’anisotropie a été quantifiée. Le rôle de l’absorption et du déphasage optique dans la détection a été établi. L’observation de plusieurs ondes de spin a permis la détermination de la constante d’échange en fonction de la concentration en phosphore. J’ai montré que celle-ci variait peu, contrairement aux prédictions théoriques.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

Systematic study of the spin stiffness dependence on Phosphorus alloying in (Ga,Mn)As ferromagnetic semiconductor

We study the dependence of the spin stiffness constant on the phosphorus concentration in the ferromagnetic semiconductor (Ga,Mn)(As,P) with the aim of determining whether alloying with phosphorus is detrimental, neutral or advantageous to increase the spin stiffness. Time resolved magneto-optical experiments are carried out in thin epilayers. Laser pulses excite two perpendicular standing spin wave modes which are exchange related. We show that the first mode is spatially uniform across the layer corresponding to a $k\approx$0 wavevector. From the two frequencies and k-vector spacings we obtain the spin stiffness constant for different phosphorus concentrations using weak surface pinning conditions. The mode assessment is checked by comparison with the spin stiffness obtained from domain pattern analysis for samples with out-of-plane magnetization and with ferromagnetic resonance experiments when more than one spin wave mode is observed. The spin stiffness is found to exhibit little variation with phosphorus concentration in contradiction with ab-initio predictions

Effets de la taille de grain et de la déformation plastique sur un acier magnétique massif

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Spin transfer and spin-orbit torques in in-plane magnetized (Ga,Mn)As tracks

International audienceCurrent-driven domain wall motion is investigated experimentally in in-plane magnetized (Ga,Mn)As tracks. The wall dynamics is found to differ in two important ways with respect to perpendicularly magnetized (Ga,Mn)As: the wall mobilities are up to ten times higher and the walls move in the same direction as the hole current. We demonstrate that these observations cannot be explained by spin-orbit field torques (Rashba and Dresselhaus types) but are consistent with nonadiabatic spin transfer torque enhanced by the strong spin-orbit coupling of (Ga,Mn)As. This mechanism opens the way to domain wall motion driven by bulk rather than interfacial spin-orbit coupling as in ultrathin ferromagnet/heavy metal multilayers