Experimental evidence and theoretical criteria for a local-field rotational correlation length in metallic spin glasses.

Abstract

Detailed measurements of the temperature and field dependence of the ac susceptibility \ensuremath{\chi} for the spin glass Cu-${\mathrm{Mn}}_{\mathrm{x}}$ reveal a new cusp transition whose locus is a line in the \ensuremath{\chi}-T plane, independent of x. We have formulated a modified mean-field theory incorporating spin clusters whose parameters are deduced from a fit to the data. We find a correlation length associated with the rotational coherence of the local field and identify the cusp line as a physical feature corresponding to the divergence of the correlation length at the transition temperature ${T}_{g}$. We find that our data are well represented by scaling relations both above and below ${T}_{g}$, and from these relations we evaluate the critical exponents \ensuremath{\delta}, \ensuremath{\gamma}, \ensuremath{\delta}', and \ensuremath{\gamma}'.