Measurement of the Spin-Glass Order Parameter in AmorphousGd0.37Al0.63

Amorphous films of composition ${\mathrm{Gd}}_{0.37}$ ${\mathrm{Al}}_{0.63}$ are found to exhibit a transition to a spin-glass state below 16 K. The magnetic properties show thermal hysteresis and relaxation below the spin-glass transition. The susceptibility maximum at 16 K, when measured in dc fields ≤10 Oe, sharpens into an asymmetric cusp, consistent with the Edwards-Anderson picture of the transition as one into a random, but rigid, state. Using the theory of Sherrington and Kirkpatrick, we extract the spin-glass order parameter from the observed cusp, and find deviations from simple mean-field behavior.