Scaling of susceptibility and the size of the critical region in an amorphous GdAl spin glass (invited)

We extend our earlier SQUID magnetometry studies of the susceptibility of amorphous Gd37A63 spin glass to a temperature range 5≤T≤100 K and a field range 0.5≤H<50 000 Oe. This enables us to determine the size of the critical region around the spin glass transition at TG=15.5 K; it extends to approximately 22 K in temperature and 15 000 Oe in field. We show that the range of reduced temperature t=(T-T G)/TG for spin glass critical behavior is determined by the parameter 1/Z1/2, where Z is the number of interacting neighbors, in rough agreement with experiment, and that the field range can be estimated from a crossover relation Hαtφ/2. We also find that nonanalyticity in χ(H) as H→0 persists at all temperatures below T G and argue that this can cause apparent nonanalyticity above T G as well in the presence of sample inhomogeneity.