Photoinduced Changes in the Crystal Anisotropy of Si-Doped YIG

It is found that the cubic magnetocrystalline anisotropy of Si‐doped YIG can be changed by exposing a single crystal to light at 77 or 4.2 K. The experiment is done using a (110) plate sample in a rotating sample magnetometer (RSM). Doping levels of 0.01 to 0.017 Si per formula unit Y₃Fe₅O₁₂ have been studied. The experimental problem is to distinguish changes in the crystal anisotropy from changes in the induced anisotropy, since both are influenced by light. This separation is possible by analysis of the RSM outputs at different frequencies and phase angles. We observe changes in the quantity ($-\frac{3}{2}{K}_1-\frac{1}{4}{K}_2$ ); the changes are a few percent in magnitude, occur within a few seconds or tens of seconds after the light is turned on, and persist for long times (many minutes) after the light is turned off. For low levels of Si doping, irradiation at 77 K produces large changes in the part of the cubic anisotropy attributable to the Fe²⁺ present. The measured change in anisotropy for all samples is an increase in magnitude at 77 K, but a decrease at 4.2 K. The effect is not observed in Ca‐doped YIG, confirming previous conclusions that ferrous ions are principally responsible for photoinduced anisotropy effects.