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This thesis fits in the framework of magnetic materials for microwave applications. The magnetic materials most used in microwave devices are ferrites, especially garnets, which have a very low magnetic damping (about 0.0001). The needs of miniaturization in cur- rent technologies bring some problems related to the integration of ferrites in microwave components. Theses materials, containing iron oxides, generally require very high deposi- tion temperatures that may damage other parts within a same circuit. One solution lies in the use of ferromagnetic materials, which can be deposited at moderate temperatures. However, this type of material usually has high damping factors making them incompa- tible with the characteristics desired in microwave components. In this context, the Heusler alloys are particularly attractive. Indeed, the latter have high magnetizations and Curie temperatures, and ab initio calculations predict extremely low damping factors.
The first step of this work was to develop a Ferromagnetic Resonance setup capable of studying materials in the microwave domain. This step was followed by the preparation of epitaxial thin film of Co2MnSi, by sputtering deposition, on MgO (001) and MgO/Cr (001) substrates. A thorough structural study (RHEED, X-ray diffraction, transmission electron microscopy) allowed verifying the high crystalline quality of samples. Their ma- gnetic properties were studied by static and dynamic techniques in order to provide a complete characterization of their magnetic parameters as a function of thickness : satu- ration magnetization, exchange constant, damping factor, gyromagnetic ratio, anisotropy constants. Obtaining these parameters was assisted by modeling based on numerical tools developed during this work.
The samples studied show low magnetic damping factors ranging between 0.002 and 0.007. The magnetic parameters (magnetocrystalline anisotropy, gyromagnetic factor) are strongly modified with the implementation of a Cr buffer layer. This suggests that the magnetic properties of Heusler alloys thin films are closely related to strains at interfaces.
This work shows that Co2MnSi could constitute a building bloc for the realization of microwave components. The buffer layer engineering is set to be a key to making these alloys compatible with the needs of current technologies. This work should make possible the study of more complex systems such as magnonic crystals based on Heusler alloys.