Irreversibility crossover in a Cu:Mn spin glass in high magnetic fields: Evidence for the Gabay-Toulouse transition

The longitudinal component of the zero-field-cooled (${\mathit{M}}_{\mathrm{ZFC}}$) and field-cooled (${\mathit{M}}_{\mathrm{FC}}$) magnetization of dilute Cu:Mn has been measured in magnetic fields between 2 G and 30 kG. The difference, Δ${\mathit{M}}_{\mathrm{irr}}$=${\mathit{M}}_{\mathrm{FC}}$-${\mathit{M}}_{\mathrm{ZFC}}$, is taken to be the irreversible magnetization. Above ≊500 G, a weak irreversibility and a strong irreversibility are observed. The onset temperature of the former, or weak irreversibility, follows the Gabay-Toulouse H-T relation with a coefficient close to the mean-field value for a Heisenberg system. The onset temperature of the latter is found to have quantitative agreement with the mean-field d’Almeida-Thouless–like H-T crossover relation for longitudinal freezing in a Heisenberg system.