THE MAGNETIC TORQUE OF THE HEAVY-FERMION SYSTEM UPD2AL3

The basal-plane anisotropy of the antiferromagnetic phase of the hexag onal heavy-fermion superconductor UPd2Al3 has been studied via the mag netic torque. Torque measurements were performed as functions of magne tic field and angle, with the field rotated in the a-b-plane, at tempe ratures between 4.2 and 30 K and in fields of up to 20 T. We interpret our results within a mean-field model and derive expressions for the basal-plane anisotropy energy. Further, we studied the anisotropy and temperature dependence of the metamagnetic transition of UPd2Al3 at 18 T and we discuss its nature.