Non-equilibrium magnetic response in concentrated spin-glass Au0.89Fe0.11 alloy

We report a detailed study of dc magnetization and ac susceptibility performed on the zero field cooled (ZFC.) and field cooled (FC..) state of polycrystalline Au0.89Fe0.11 alloy. The temperature variation of ZFC and FC dc magnetization at low fields shows a distinct peak around T-f = 33 K, which indicates the cooperative freezing of the finite size spin clusters. A weak thermomagnetic irreversibility between ZFC and FC magnetization appears at a temperature T-tr, which is slightly below T-f. Further down the temperature at T-sh < T-tr, the ZFC and FC magnetization curves exhibit strong thermomagnetic irreversibility. The ac susceptibility recorded after cooling in presence of field shows significant dispersion below T-f, and also, the FC state of Au0.89Fe0.11 alloy exhibits a pronounced memory effect in the dc magnetization which clearly underline that the FC state is not an equilibrium state. In contrast to the general perception obtained through the mean-field theories of thermodynamic phase transition in spin-glass envisaging the FC state to be an equilibrium state, the present experimental results clearly indicate that the energy landscape of the FC state of Au0.89Fe0.11 alloy is a nontrivial one.

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We conducted a detailed study on the dc magnetization and ac susceptibility of the ZFC and FC state of polycrystalline Au0.89Fe0.11 alloy. The temperature dependence of ZFC and FC magnetization shows a distinct peak at T-f = 33 K, indicating the cooperative freezing of finite size spin clusters. A weak thermomagnetic irreversibility is observed between ZFC and FC magnetization at T-tr, slightly below T-f. At lower temperatures (T-sh < T-tr), strong thermomagnetic irreversibility is observed in the ZFC and FC magnetization curves. The AC susceptibility recorded after cooling in the presence of a field exhibits significant dispersion below T-f, and the FC state of Au0.89Fe0.11 alloy shows a pronounced memory effect in the dc magnetization, indicating that it is not an equilibrium state.