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

Abstract

Superconducting-quantum-interference-device magnetometry is used to study the long-time cooling-rate dependence of the susceptibility cusp of the spin-glasses, $\mathrm{Cu}\mathrm{Mn}$ 4.6 at.% and $Al\mathrm{Gd}$ 37 at.%. Over a range of time delay $\Delta T=6\mathrm{} \mathrm{to} 2400$ min per temperature change $\Delta T=0.2\mathrm{}$ 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 ($\nu =10\mathrm{} \mathrm{to} 30000$ Hz). Thus, they appear to be inconsistent with current nonequilibrium models for spin-glass freezing and rather suggest a phase-transition phenomenon.