Neutron-spin-echo study of the reentrant spin glass EuxSr1−xS

Abstract

Neutron‐spin‐echo (NSE) experiments were performed on polycrystalline samples of Eu_xSr_1−xS for x=0.4 and 0.54 in the temperature range of 1.2<TQ−¹. The x=0.4 sample exhibits a paramagnetic (PM) to spin‐glass (SG) transition near T_g ∼2 K. In the x=0.54 sample, large ferromagnetic correlations develop below 5 K and a SG state appears at lower temperatures. In the NSE experiment, the spin‐spin correlation function S(Q,t) is measured directly for times between 0.03<tQ dependence in the dynamics and the spins are essentially frozen over the time range explored. On heating the x=0.4 sample, the spins start to fluctuate more rapidly, but no dramatic change occurs around T_g. On heating the x=0.54 sample, S(Q,t) decreases rapidly with time. Near 5 K, S(Q,t) is exponential (e^−Γt) with Γ being strongly Q dependent. Measurements of the depolarization of the scattered beam confirms the absence of true long‐range ferromagnetic order below T_c.