IRREVERSIBILITY CROSSOVER IN A CU-MN SPIN-GLASS IN HIGH MAGNETIC-FIELDS - EVIDENCE FOR THE GABAY-TOULOUSE TRANSITION

The longitudinal components of the zero-field-cooled (M(ZFC)) and field-cooled (M(FC)) magnetization of dilute Cu:Mn have been measured in magnetic fields between 2 G and 30 kG. The difference, DELTA-M(irr) = M(FC) - M(ZFC), is taken to be the irreversible magnetization. Above almost-equal-to 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 agree quantitatively with the mean-field d'Almeida-Thouless-like H-T crossover relation for longitudinal freezing in a Heisenberg system.