Photo-Induced Magnetic Effects in FZ YIG Single Crystal

Highly pure single crystals of YIG were obtained by an FZ method, and a remarkable photoinduced change in permeability was observed. The permeability of samples held at a temperature of 77K was decreased by more than 90% by illumination. The photoinduced change remained, to some extent, at temperatures up to about 260 K. By annealing at 1100°C (in an oxygen atmosphere for six hours) in the sample preparation stage, the magnitude of the effect was reduced to 40%. After samples at 77K were strongly illuminated, the loss factor below 5 kHz showed a pair of peaks, in contrast with the flat curve for unilluminated samples on warming to 300 K. The activation energies corresponding to the peaks were found to be 0.3 and 0.1 eV. The mechanism of the effect is discussed in relation to relaxation processes related to these peaks, and F^o centers, or oxygen vacancies with two trapped electrons, are thought to play an essential role.