Elastic Anomalies in Fe–Al Spin Glasses

Abstract

The temperature dependence of elastic constants of quenched Fe 1- x Al x ( x =0.26, 0.30 and 0.32) single crystals was measured by a ultrasonic pulse-echo technique from 4.2 K to 300 K under applied magnetic fields. For the ferromagnetic alloy with x =0.26, the Δ E effect was observed in the C 44 mode. The reentrant spin glass alloy with x =0.30 also shows the Δ E effect in C 44 above 90 K, which corresponds to the reentrant spin glass freezing temperature, T f . Below T f the Δ E effect completely disappears, indicating freezing of spins or magnetic clusters. In the spin glass alloy with x =0.32 a slight softening of C 44 was observed around T f determined by magnetization measurements. These observations indicate that the elastic measurement provides an useful experimental method of determining the spin glass freezing temperature, in particular, for reentrant type spin glasses.