Phase-transition problem and magnetic short-range order in Heisenberg spin glasses.

Abstract

We report on measurements of the nonlinear susceptibility for the spin glasses ${\mathrm{Eu}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{S}}_{y}{\mathrm{Se}}_{1\ensuremath{-}y}$ which, depending on the concentration $y$, possess either ferromagnetic or antiferromagnetic short-range order. Only for the case of ferromagnetic short-range order does the nonlinear susceptibility diverge for $T\ensuremath{\rightarrow}{T}_{f0}$; for antiferromagnetic short-range order it is nearly temperature independent for $T\ensuremath{\rightarrow}{T}_{f0}$. The results are in favor of a nonequilibrium transition at ${T}_{f0}$ and demonstrate the misleading role of magnetic short-range order developing above the freezing temperature for the phase-transition problem in real spin glasses.