Non-Mean-Field Interpretation of the Irreversibility Line in Spin-Glasses

Abstract

Susceptibility data on an amorphous GdAl spin-glass show an irreversibility onset line $t=\ensuremath{-}A_{\ensuremath{-}}H^{\frac{2}{{\ensuremath{\varphi}}_{\ensuremath{-}}}}$ and a susceptibility crossover line $t=+A_{+}H^{\frac{2}{{\ensuremath{\varphi}}_{+}}}$ ($t$ is reduced temperature; $H$ is field). The exponents $\ensuremath{\varphi}$ are both close to 3, and the amplitudes $A$ differ only by a factor of 2. In contrast to earlier explanations of the irreversibility in terms of a de Almeida-Thouless mean-field instability, here both crossovers are explained in terms of a non-mean-field scaling theory.