New information on the spin-glass state of AuFe from transport measurements

Abstract

The author has investigated the influence of the state of remanent magnetisation on the transverse and longitudinal magnetoresistances of AuFe spin-glass alloys. Large hysteresis effects have been observed for the first time. Whatever the magnetic history of the sample, the magnetoresistance depends only on the macroscopic magnetisation m= chi H+m_r where chi H and m_r are the reversible and the irreversible magnetisations. This dependence is very simple and quadratic in m: Delta rho / rho ₀=- alpha ( chi H+m_r)². The coefficient alpha is found to be almost independent of the concentration when this concentration is varied from 200 PPM to 70000 PPM (at least). These data contradict a cluster model for AuFe spin-glass alloys but are consistent with a homogeneous picture for both the reversible and the irreversible magnetisations. The anisotropy field concept is not found to be useful in the case of AuFe spin-glass alloys.