Measurements of the magnetic anisotropy of gadolinium

Abstract

Measurements of the magnetocrystalline anisotropy constants of gadolinium have been made using a torque method. Torque observations were made on a single crystal oblate spheroid of the material which contained the hexagonal axis in its plane. The system for measuring torque was null-reading and a counter - torque was provided by passing currents through a small coil running in an instrument magnet. Balancing was done automatically with a photocell feed-back amplifier system. Values of the anisotropy constants have been derived from observed torque curves by a least - squares fit to the theoretical curves. The process was carried out on the Perranti Pegasus computer. The anisotropy constants were obtained over the temperature range from the Curie point (~289 K) to 20 K and they are presented graphically. K(_1) found to be negative below ~ 235 K indicating an easy direction in the basal plane and the crystal only exhibits a uniaxial character above this temperature. The change in sign of prevents any comparison with the Zener theory.