Magnetic anisotropy and spin-reorientation in HoAl2

Torque measurements have been performed at several temperatures and magnetic fields, on a single crystal of HoAl₂ in the (1 1 0) plane. The easy magnetization direction changes from the [1 0 0] to [1 1 0] near T_R = 20 K in magnetic fields between 0.2 and 1.6 T. At temperatures below T_R a new non-major cubic symmetry easy direction appears which rotates with temperature in the plane of the sample. This behaviour and that of the complete torque curves have been interpreted on the basis of a single ion model.