Basal-plane anisotropy forSm2Co17:The crucial role ofJmixing

Abstract

The sixth-order basal-plane anisotropy constant ${K}_{3}^{\ensuremath{'}}$ was deduced at different temperatures for ${\mathrm{Sm}}_{2}{\mathrm{Co}}_{17}.$ The values were derived from measurements of the anisotropy field ${H}_{A}$ performed along the two hard directions corresponding to the crystallographic a and b axes. In the frame of a single-ion model with exchange and crystal field, ${K}_{3}^{\ensuremath{'}}$ is proportional to the sixth-order crystal-field term. However, the sixth-order term is zero for the ${\mathrm{Sm}}^{3+}$ ion within the ground state multiplet. The experimental data were then compared with a curve ${K}_{3}^{\ensuremath{'}}(T)$ calculated considering the three lowest-lying J multiplets. Using perturbation theory it was shown that ${K}_{3}^{\ensuremath{'}}$ is directly proportional to the sixth-order crystal-field parameter ${B}_{66}$ even in the case of strong J mixing due to the exchange field. The best fit of the experimental data was obtained by means of a set of parameters which are consistent with those given in the literature, and in particular an accurate determination of ${B}_{66}$ was possible. The results of the theoretical calculation were also compared with anisotropy field measurements on the isostructural compound ${\mathrm{Er}}_{2}{\mathrm{Co}}_{17},$ for which the J mixing is not expected to be significant.