Room-temperature spin glass and its photocontrol in spinel ferrite films

Room-temperature spin-glass states have been found in (Mg,Fe){Mg,Fe,Ti}(2)O -4 spinel ferrite thin films formed on Al2O3(0001) and SrTiO3(111) substrat es. This elevated-temperature spin-glass state has been achieved by the fin e tuning of spin states through the control of composition, random oxygen d eficiencies, and the stress induced by the film/substrate lattice mismatch in the ferrite films. We have demonstrated the change of magnetic state by means of light irradiation from spin glass to a ferrimagnet over a wide ran ge of temperatures below 290 K. The direct photoexcitation of spins with ph oton energy of 2.0 eV, which corresponds to the spin excitation energy for Fe ions, is the most effective for realizing photoinduced magnetization. (C ) 2000 American Institute of Physics. [S0003-6951(00)01750-2].