Critical effects in the reversible, nonlinear susceptibility ofPdMn spin glasses

The ac susceptibility of two PdMn spin glasses containing 5.0 and 5.5 at. % Mn have been measured as a function of temperature in a large number of static biasing fields between 0 and 500 Oe in the vicinity of the spin-glass (SG) temperature $T_{\mathrm{SG}}$. Our analysis of the field dependence of these data both above and below $T_{\mathrm{SG}}$ provides the first experimental observation of a nearly symmetric divergence in the coefficients of the leading terms in $H^2$ and $H^4$ in the nonlinear reversible susceptibility as T approaches $T_{\mathrm{SG}}$ from above and below. The exponents which characterize the temperature dependence of the divergences are in good agreement with estimates obtained above $T_{\mathrm{SG}}$ by other authors.