TB MAGNETIC-MOMENT BEHAVIOR IN A GD SINGLE-CRYSTAL - NUCLEAR ORIENTATION STUDY

Low-temperature nuclear orientation has been used to stud; the behavio ur of the Tb magnetic moment in a Gd + 1 at.% Tb single crystal. The g amma-ray anisotropy of several Tb-160 lines was monitored in the tempe rature range of 5-50 mK and in the external magnetic field (B-ext) ran ge of 0-8.5 T. The field was applied either along the a- or along the c-axis of the Gd single crystal. In the case of B-ext parallel to the a-axis the Tb magnetic moment was found to be almost aligned along B-e xt even at very low fields, as expected because the hexagonal basal pl ane is an easy magnetization plane for the Tb ion in terbium metal. On the other hand, when B-ext is along the c-axis the Tb magnetic moment rotates very slowly towards the c-axis. Even at B-ext = 8.5 T the Tb magnetic moment is not along the direction of B-ext. This is in contra st to the fast saturation of the gadolinium ions in pure Gd. Apparentl y, the Tb-Gd exchange interaction is in competition with the crystal f ield acting on the To ion in a hexagonal lattice, our data indicates t hat at B-ext = 8.5 T along the c-axis the angle between the Tb magneti c moment and the applied field is of the order of 30 degrees.