Temperature Dependence of the First- and Second-Order Cubic Anisotropy Constants in EuSe

The first- and second-order cubic anisotropy constants in EuSe have been measured as a function of temperature from 1.15 to 10 °K. Ferromagnetic resonance measurements at $K$-band frequencies (24 GHz) assured single-domain samples and internal fields high enough to produce the ferromagnetic phase over the entire temperature range. The results show structure in addition to a very weak temperature dependence below the zero-field ordering temperature (4.6 °K). The results are not explained by a single-ion theory of anisotropy. Changes in the anisotropy constants as well as the linewidth correspond in temperature to observed zero-field phase changes, indicating that the current description of EuSe, as being in a simple ferromagnetic phase for ${\overrightarrow{\mathrm{H}}}_{\mathrm{int}}>2\mathrm{}$ kOe, is incomplete.