Test of Spin-Wave Theory with Precision Magnetization Measurements

Abstract

Magnetic moment measurements of single crystal nickel, made from 4.2° to 290°K in a uniform magnetizing field applied along principal crystallographic directions, are presented. The precision of the measurements permits accurate comparison with predictions of spin‐wave theory. At low temperatures (less than 150°K) ${\mathrm{\Delta \sigma \hspace{0.17em}\propto \hspace{0.17em}T}}^{\text{1.5±0.1}}$ in agreement with spin‐wave theory. Deviations from the $T^{\text{1.5}}$ law, observed at high temperatures, are much larger than predicted by high‐order terms of spin‐wave theory. Possible sources for the effect, including temperature variation of $g$ value and/or exchange constant, are summarized. Estimates of exchange constant are given.