Irreversible response in spin-glasses: An experimental study in amorphous Fe-Mn

Abstract

The equilibrium and nonequilibrium susceptibilities ${\chi }_{\mathrm{e}}$ and ${\chi }_{\mathrm{ne}}$ of the spin-glass ${\left({\mathrm{Fe}}_{0.64}{\mathrm{Mn}}_{0.36}\right)}_{75}$ ${\mathrm{P}}_{16}$ ${\mathrm{B}}_6$ ${\mathrm{Al}}_3$ have been measured as functions of temperature ($4.2<~T<~80$ K) and a cooling field ($8 \mathrm{Oe}<~H<~2 \mathrm{kOe}$). A phase transition occurs at a temperature $T_c\mathrm{}\left(H\right)\mathrm{}$ below which the irreversible response $\Delta \mathrm{}\left(T\right)\mathrm{}\propto T({\chi }_{\mathrm{e}}-{\chi }_{\mathrm{ne}})$ appears. $T_c\mathrm{}\left(H\right)\mathrm{}$ decreases from the freezing temperature ($T_f=41.6\mathrm{}$ K) as $H^{0.75\pm 0.1}$. For small $\tau \equiv 1-\frac{T}{T_c\mathrm{}\left(H\right)\mathrm{}}$, $\Delta$ behaves as $A\tau +B{\tau }^2$ with field-dependent coefficients $A$ and $B$ and $A(H=0\mathrm{})=0\mathrm{}$. The results are compared with the predictions of the mean-field theory of spin-glasses.