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Composites multiferroїques pour dispositifs magnéto-électriques intégrés

Abstract : This work is focused on the study of laminated magnetoelectric composites aiming at the realization of novel components integrated on silicon, such as variable inductors. Thanks to the mechanical coupling between two adjacent layers of ultra-soft magnetostrictive and piezoelectric materials it is possible to obtain an indirect magnetoelectric effect which is several orders of magnitude higher than in natural multiferroics. Firstly, we used an energy-based phenomenological approach to describe a range of expected effects in such laminated magnetoelectric composites. Thereupon, macroscopic magnetoelectric composites based on piezoelectric MFC substrates and magnetostrictive thin films of FeCoB were realized. The study of the magnetoelectric coupling vs. FeCoB composition leads to the identification of the key material parameters, such as λs/Ms, that are essential for high magnetoelectric effect. A record magnetoelectric coefficient of 250 V∙cm‐1Oe‐1 is obtained. In parallel, a specific Kerr effect microscope devoted to live observation of the magnetic domains change vs. applied electrical field was developed. For the first time, direct observation of the magnetic easy-axis rotation with voltage in such composites is reported. The second part of this work concerns the design, simulation, fabrication and characterization of a hybrid MEMS variable inductor. This device exploits the indirect magnetoelectric effect between a PZT sol gel driving element and a FeCoB-based inductive element. The unusual multi-physics nature of the device prompted us to deploy a set of electrical, mechanical, optical and magnetic tests throughout the manufacturing. The results conclude with partially functional proof of concept, mainly due to the lack of management of internal stress during the fabrication. Areas for improvement of design, materials and process are identified.
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Gor Lebedev. Composites multiferroїques pour dispositifs magnéto-électriques intégrés. Energie électrique. Université de Grenoble, 2012. Français. ⟨tel-00782536⟩

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