Random local anisotropy in spin glasses

Field-cooled ${\mathrm{Au}}_{82.5}$ ${\mathrm{Fe}}_{17.5}$ in a large demagnetization configuration shows a very pronounced decrease of the magnetization below 50 K, while on field heating, a steep increase of the magnetization follows above 50 K. This behavior is explained by a previously proposed model involving the effect of quasirandom local anisotropy on magnetic cluster moments, which is overcome at ∼50 K by thermal activation. The time-dependent, viscous reorientation of the cluster moments also needs to be taken into consideration.