Light modified switching properties of garnets and ferrites

The influence of light on the switching behavior of Si-doped Y
3
Fe
5
O
12
and Co-substituted Ni-Zn ferrites is investigated. After irradiation with light, YIG (Si) has an extremely square hysteresis loop, and the switching transients display anomalous behavior. When a step field is applied, there is a certain period of time during which no flux is switched irreversibly. After this delay, which depends on the amplitude of the applied step field, the material switches in the normal way. At 4.2 and 77°K these changes are permanent; at 200°K the effects disappear after illumination is terminated. The results are discussed in terms of a two-center model, which was proposed earlier to explain results for changes in permeability. Co-substituted Ni-Zn ferrites show similar behavior already in the nonirradiated state. Irradiation increases the coercive force and also the break-free behavior becomes more pronounced. These changes are still permanent at 200°K.