Intrinsic and Field-Induced Anisotropy of Si-Doped YIG from 4.2 to 300 K

Abstract

The effect of Si additions on the crystal anisotropy and on the field-induced anisotropy in yttrium iron garnet crystals has been measured from 4.2 to 300 K, using a rotating-sample magnetometer (RSM). Use of the RSM makes it possible to separate the effects of induced anisotropy from those of the crystal anisotropy, which has not been possible in previous torque and resonance measurements. The experiments reported here were all done with the sample shielded from light, so that photoinduced effects have been deliberately avoided. Silicon in amounts up to about one atom per formula unit Y3Fe5O12 has almost no effect on the anisotropy of YIG at temperatures above about 150 K; at lower temperatures there is a large positive contribution to K1. Over most of the composition range studied, K1 (negative for pure YIG) becomes positive at low temperatures. The change in K1 is approximately linear with Si content, and hence presumably with Fe2+ content. The induced anisotropy, which is also measured in the RSM experiment, becomes significant at the same temperature (150 K) where departures from the anisotropy of pure YIG are observed. This induced anisotropy is remarkable in that it shows a very wide range of relaxation times (10−3–10−1 sec in our work, and 1–100 sec in previous work) which vary relatively slowly with temperature.