Long-time cooling-rate dependence of spin-glass freezing

Superconducting-quantum-interference-device magnetometry is used to study the long-time cooling-rate dependence of the susceptibility cusp of the spin-glasses, CuMn 4.6 at.% and AlGd 37 at.%. Over a range of time delay ΔT=6 to 2400 min per temperature change ΔT=0.2 K, no change is observed in the position of the cusp. These long-time results do not fit an extrapolation from Tholence's earlier ac susceptibility data as a function of frequency (ν=10 to 30000 Hz). Thus, they appear to be inconsistent with current nonequilibrium models for spin-glass freezing and rather suggest a phase-transition phenomenon.