Critical Line for Strong Irreversibility in Spin-Glass and Ferro-Spin-Glass Alloys

Torque measurements have been made as a function of temperature on a Cu-2-at.%-Mn and a Au-18-at.%-Fe alloy. At a field-dependent temperature $T^{*}\mathrm{}\left(H\right)\mathrm{}$ torque effects go to zero indicating the frontier for the low-temperature strong-irreversibility regime. For the $\mathrm{Cu}\mathrm{Mn}$ sample the present experimental $T^{*}\mathrm{}\left(H\right)\mathrm{}$ curve coincides with the calculated mean-field-model de Almeida-Thouless line. For the $\mathrm{Au}\mathrm{Fe}$, $T^{*}\mathrm{}\left(H\right)\mathrm{}$ also follows the behavior predicted for the strong-irreversibility crossover on the mean-field model.