Photomagnetic effects

Direct influence of electromagnetic radiation on magnetic properties has been detected at low temperatures (T < 150°K) in Si-doped YIG (Y3Fe5-xSixO12) and in Ga-doped CdCr2Se4(Cd1-yGayCr2Se4. Its manifestations are 1) a change in crystalline anisotropy observed in ferromagnetic resonance and torque measurements at high dopes ( ) and 2) a reduction in initial permeability and an increase in coercive forceoccurring for low dopes ( ). These changes are produced by irradiation with light of wavelength <1.3 μm. The effects depend upon the product of light intensity and irradiation time, and are attributed to light-induced electron transfer resulting in a redistribution of Fe²⁺(or Cr²⁺) ions. At low temperature the redistribution and its manifestations are permanent; at higher temperature there is a competition with thermal electron motion. Quantitative results of a simple 2-center model are shown to agree well with experiment. Potential applications are in the field of information storage.