Gold-iron spin glasses in low DC fields. I. Susceptibility and thermoremanence

Detailed studies of low-field susceptibility chi (T), thermoremanence and isothermal remanence in gold-iron alloys containing 0.25, 2, 4, 7at% Fe are presented. The susceptibilities show sharp but not discontinuous reversals of slope at T f . Below the maximum in chi (T), the zero-field cooled susceptibility shows a marked shoulder at 0.6T f which coincides with a maximum in the incremental isothermal remanence as a function of temperature. Below T f the total magnetisation decreases slowly, flattening out to a constant value of approximately 0.9M(T f ). Thermoremanence increases almost linearly with decreasing temperature from zero at T f . Both total magnetisation M(T)/M(T f ) and TRM/M(T f ) follow functions of temperature which are almost independent of composition. The results suggest a finite susceptibility at T=0, approximately 0.35 chi (T f ) indicating the presence of a reversible component to the magnetisation at absolute zero. Analogies with the behaviour of rock magnetism are indicated and the variation of TRM is analysed in terms of a spectrum of blocking temperatures deduced from isothermal remanence experiments.