Ferromagnetic resonance spectra in reduced Ca-rich CaGe:YIG film

Abstract

Ferromagnetic resonance (FMR) spectra have been obtained in an 11-μm-thick charge uncompensated garnet film having the composition of Y2.0Ca1.0Ge0.9Fe4.1O12 as a function of the reducing time up to 80 h in a solution of FeCl2 and in a N2 atmosphere at 1100 °C for up to 16 h. The temperature dependence of the cubic anisotropy field, the effective uniaxial anisotropy field, the g factor, and the linewidth were determined between 80 K and room temperature. The results show that, contrary to previous data based on the measurements of averaged properties, surface reduction is the dominant process and a surface layer having magnetic properties that differ significantly from the bulk region of the film is developed during reduction. The internal field parameters of the bulk layer of the film in the case of FeCl2 reduction are observed to be only slightly changed from those of the as-grown material, while for the nitrogen reduction process the growth-induced uniaxial anisotropy of the film is annealed out. The results are interpreted in the frame of the reduction of the charge compensating non-S-state Fe4+ ions to Fe3+ with the introduction of oxygen vacancies.