Isothermal anisotropy rotation in a Au-Fe spin-glass alloy

Magnetization-vector measurements were made on a slowly rotating disk sample of Au₈₅ Fe₁₅ after cooling to 4.2 K from above T_g (=52 K) in a 15-kOe field that saturates the thermoremanence. For M_T, the magnetization component transverse to the applied field H, results are shown as HM_T vs θ, the sample-rotation angle relative to H, for θ cycled between 0°and 180°at each value of H. For H≲0.1 kOe, HM_T varies nearly reversibly in simple accord with an anisotropy field H_K (0.41 kOe in size) that rotates rigidly with the sample. At higher H, the rotational hysteresis grows rapidly until, for H≳0.4 kOe, another simple but highly irreversible behavior is observed. From this behavior, it is deduced that H_K rotates relative to the sample isothermally when the torque on it exerted by the sample magnetization reaches the magnitude of a frictional torque. The frictional-torque coefficient is seen to decrease steadily with increasing H, as confirmed by direct measurements of the rotations of the remanence that result from sample rotations in various H at 4.2 K.