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Synthèses, mise en forme et étude des propriétés magnétiques de ferrites (NiZnCuCo)Fe2O4 en fréquence

Abstract : The high commutation rate of the wide gap semiconductor (GaN) allows operating with switching frequency above 1MHz in power converters. However, current magnetic materials comprising passive components in power converters cannot sustain the rise in the operating frequency, especially above 1 MHz. The main limitation comes from the sharp increase in power losses creating thermal dissipation inside the magnetic core. The core-losses are due to dynamic magnetization process (including domain wall movement and spin rotation) and they increase with the frequency. (Ni,Zn,Cu)Fe2O4 spinel ferrite is currently the best magnetic material with limited core-losses. The objective of the Ph.D. is to experimentally contribute to the understanding of the link between the microstructure and the static and dynamic magnetic properties.Synthesis process of (Ni,Zn,Cu)Fe2O4 spinel ferrite such as sold-state reaction and Pechini method were studied. The structural and magnetic properties were systematically measured and correlated together. We managed to master the elaboration and produce high density ferrite with controlled grain size (about few µm) and high density (d>92% dth). Results suggest that ferrites synthesized by Pechini method can be considered as an interesting basis for the design of low-loss magnetic components alternatively to the conventional route.The analysis on core-loss showed that the results are compatible with a dissipation mechanism linked to spin damping inside domain walls. It justifies the production of well-densified massive pieces composed of small grains and cobalt to obtain low core-loss for large amplitude excitation (up to 25mT).
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Submitted on : Wednesday, June 27, 2018 - 11:31:06 AM
Last modification on : Tuesday, October 6, 2020 - 8:38:48 AM

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Gaëlla Frajer. Synthèses, mise en forme et étude des propriétés magnétiques de ferrites (NiZnCuCo)Fe2O4 en fréquence. Science des matériaux [cond-mat.mtrl-sci]. Université Grenoble Alpes, 2018. Français. ⟨NNT : 2018GREAY002⟩. ⟨tel-01824459⟩

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