Thermal variation of imaginary part of permeability in previously photoexcited YIG single crystal

A photoinduced decrease in permeability µ' is observed over 90% at 77 K in the highly pure single crystal of YIG grown by a floating zone method. Furthermore, an imaginary part of permeability µ'' is found to show an increase unlike µ' on illumination at 77 K and on warming the double peaks below 10 kHz. From the frequency dependence of these peaks, the activation energies obtained are 0.1 and 0.3 eV, respectively. The peak at lower temperature shows a maximum, whereas the other peak at higher temperature shows a monotonous increase with an increase of strength of illumination. These features have been discussed in terms of a two levels-two minima model.