| Popis: |
We have measured the static susceptibility $\ensuremath{\chi}$ 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 $5{T}_{f}$ (${T}_{f}$ is the freezing temperature), a Curie-Weiss law is obeyed with an effective Bohr magneton number ${p}_{0}=(5.07\ifmmode\pm\else\textpm\fi{}0.10){\ensuremath{\mu}}_{B}$ which is, within 2%, independent of concentration, and a paramagnetic Curie temperature $\ensuremath{\Theta}$ which is a strong, linear function of the concentration. Below $5{T}_{f}$ 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. |
