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MICROWAVE PROPERTIES OF THIN FERRITE FILMS,
POLYTECHNIC INST OF BROOKLYN N Y MICROWAVE RESEARCH INST
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The magnetic properties of thin ferrite films were investigated both by conventional microwave methods, and by observation of the dc Hall effect voltage which is associated with ferromagnetic resonance. These measurements allow determination of the saturation magnetization, resonance linewidth or relaxation time, gyromagnetic ratio, extraordinary Hall coefficient, and magnetoresistance anisotropy. While the Hall effect measurement can be made on films too thin to measure by conventional microwave techniques, the Hall voltage is proportional to the microwave current density, and thus is largest in films of high conductivity. It has been possible thus far to study ferromagnetic resonance by the dc signal only in magnetite, while films of magnetite and nickel, magnesium, manganese, copper ferrites, mixed ferrites, and ferri-aluminates were studied by conventional microwave methods. The measurements reveal that the best films have magnetizations, gyromagnetic ratios, and linewidths which are quite comparable to those of the corresponding bulk ferrites. Films which are not prepared properly show deviations from bulk properties such as reduction of saturation magnetization and greatly increased linewidth. Possible explanations, such as strain and exchange anisotropy, are discussed. Author
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