The temperature dependence of the anomalous effective g value of BiTm:YIG

Abstract

Bi- and Tm-substituted YIG have shown [V. R. K. Murthy et al., in Digest of INTERMAG Conference (IEEE, New York, 1983)] anomalously low effective g values. The experimentally measured temperature dependence of BiTm:YIG shows that the effective g value decreases with decreasing temperature whereas the simple spin-wave theory predicts the opposite behavior. A recent paper [A. Lehmann-Szweykowska et al., J. Magn. Magn. Mater. 54, 1183 (1986)] predicts that the single ion anisotropy and spin-wave damping also make important contributions to the effective g value. These effects are due to the large crystal field effects of Tm in the garnet crystal host. The ground state of the Tm is J=6, L=5, and S=1. The large orbital angular momentum states enhance the spin-orbit coupling which is related to the crystal field effect. The temperature dependence of the effective g value was measured by FMR (ferromagnetic resonance) on BiTm:YIG. The experimental temperature dependence is fitted to the theoretical model and excellent agreement is obtained.