Photoinduced magnetic effects in amorphous spin glasses

We report on photoinduced magnetic phenomena in amorphous insulating spin glasses, the cobalt and manganese aluminosilicate glasses, below their freezing temperature. The homogeneity of the samples has been checked by electron microscopy. X-ray and optical-absorption measurements proved that manganese and cobalt ions are only in their divalent state. This photomagnetism cannot be interpreted by previously developed theories for other magnetic crystalline materials. A semiphenomenological theory, which assumes a pseudolocalized character of the photoinduced magnetic effects, is proposed to interpret the experimental data. All experimental results on the temperature, magnetic-field, and light-wavelength dependences of the effect strongly support the hypotheses put forward in our model. The proposed microscopic origin of the phenomenon deals with localization of nonthermalized phonons, created during the optical excitation of the 3d metal ions in the investigated amorphous compounds. Magnetic frustration in these spin glasses also limits the extension of the magnetically perturbed region.