Basal-Plane Anisotropy of Gadolinium

The magnetocrystalline anisotropy in the basal plane of gadolinium (constant K4 in the usual notation) has been determined from torque measurements on a single-crystal disk in the temperature range 4.2° to 150°K. The easy direction in the basal plane is 〈112̄0〉, corresponding to K4<0. The use of anisotropy per unit mass instead of the customary anisotropy per unit volume is suggested for measurements which extend over a range of temperature, and the symbol Kn is suggested for anisotropy-per-unit mass. The value of K4 for Gd at 4.2°K is [minus]800 erg/g, and K4 approaches zero at about 170°K. The temperature dependence of K4 follows approximately the 21st power of the magnetization as predicted by theory.