The Local Magnetic Anisotropy Effects and Magnetic Resonance of Amorphous Neodymium Transition Metal Thin Films.

Model calculations and magnetic resonance experiments were employed to investigate the microscopic and macroscopic properties of amorphous neodymium-iron and neodymium-cobalt thin films. The calculations yielding the magnetization as a function of the applied field and temperature, the coercivity, and the ordering temperature, were performed on a random dense packed model of an amorphous neodymium -iron thin film. The model includes site dependent local random anisotropy, rare-earth rare-earth, transition-metal transition-metal, and rare-earth transition-metal exchange as well as the Zeeman energy. Variation in the intersubnetwork exchange coupling was found to lead to dramatic changes in the temperature dependence of the subnetwork magnetizations. The ordering temperatures predicted by the model calculations were found to vary monotonically with the exchange coupling constants. Nd-Co and Nd-Fe samples, examined in microwave absorption experiments, were prepared by conventional thermal co-evaporation techniques. Auger analysis, energy dispersive X-ray spectroscopy and X-ray diffraction were employed to determine the chemical composition and microscopic structure of these samples. Magnetic resonance data were compared with a ferromagnetic resonance theory which treats the random local anisotropy field. The resonance signals were recognized as arising from a cooperative mode resonance. The signals were broadened by the inhomogeneity in the magnitudes of the local anisotropy fields and spatial variation in the local magnetization. Macroscopic magnetic anisotropy was also observed.