Nonlinear Susceptibilities of the Amorphous Spin Glass Fe10Ni70P20: Critical Exponents and Gabay-Toulouse Line

The nonlinear susceptibility, χ 2 , has been observed on the amorphous spin glass Fe 10 Ni 70 P 20 using a Hartshorn bridge. The critical exponents γ s =2.3±0.2 and δ=5.2±0.5 were estimated from the expressions χ 2 ∼ ε -γ s ( ε =|( T - T g )/ T g |) above T g and χ 2 ∼ h 0 2/δ-2 at T = T g ( h 0 is ac-field amplitude), which tend to confirm that the spin glass transition is characterized by critical exponents different from those of the mean field theory. The HT-phase diagram has also been determined from the anomalies of the transverse nonlinear susceptibility; χ 2 ⊥ . In the presence of a longitudinal static magnetic field, χ 2 ⊥ splits into one peak and a broad maximum with increasing the longitudinal static magnetic field. The temperature of the low temperature peak corresponds to the onset of strong irreversibility and can be assigned to the AT line, while the maximum corresponds to the GT line. These data confirm the phase diagram recently deduced by others from χ 0 ⊥ .