New magnetic properties of a dilute spin-glass

Abstract

The insulating Sr_1−xEu_xS system exhibits spin‐glass properties for x≳0.05 due to competing ferro and antiferromagnetic interactions. A scaling law x/T_f=f (ln ν) represents the frequency (ν) dependence of T_f, the temperature of the maximum of χ_a.c. (or spin‐glass freezing temperature). This frequency dependence of T_f is at least an order of magnitude bigger than in a canonical spin‐glass such as AuFe. The dipolar interaction is responsible for the anisotropy inside magnetic clusters. For xa.c., doesn’t exhibit a single maximum, but after an initial maximum or plateau around T_p it increases to a second rounded maximum, at much lower temperatures. Below T_p, which is concentration independent, a remanent magnetization appears proportional to x². Furthermore, at this temperature deviations from a Curie law of χ_a.c. increase more rapidly than x. Moreover, the frequency dependence of T_p permits a determination of a blocking energy. This energy is in agreement with the anisotropy barrier due to the dipolar interaction for a ferromagnetic pair of first neighbors. All these results support the idea of short range order for individual pairs, and small magnetic clusters which are blocked below T_p on random anisotropy directions determined by the intra‐cluster dipolar interaction. A similar change in the magnetic properties of other spin‐glasses is expected.