High-temperature susceptibility of theCuMnspin-glass

Abstract

We have measured the static susceptibility $\chi$ of a series of $\mathrm{Cu}\mathrm{Mn}$ spin-glass alloys with concentrations 1 to 6 at.% Mn in the temperature range 4 to 300 K. A sensitive pendulum magnetometer was used with external fields up to 6000 G (0.6T). For temperatures above $5T_f$ ($T_f$ is the freezing temperature), a Curie-Weiss law is obeyed with an effective Bohr magneton number $p_0=(5.07\mathrm{}\pm 0.10){\mu }_B$ which is, within 2%, independent of concentration, and a paramagnetic Curie temperature $\Theta$ which is a strong, linear function of the concentration. Below $5T_f$ there are deviations, which increase with decreasing temperature, in the susceptibility from the Curie-Weiss law. We analyze these deviations by means of the temperature derivative of the inverse measured susceptibility, a quantity which becomes very large near $T_f$. This behavior demonstrates that short-range ferromagnetic correlations and fluctuations exist among the Mn spins far above $T_f$ and further that these interactions are a precursor of the cooperative freezing at $T_f$. Our results illustrate the need for a new theoretical approach to describe spin-glass freezing.