J-mixing effects on the anisotropy of Sm₂Co₁₇

Measurements of the temperature dependence of the anisotropy field H_A for Sm₂Co₁₇, Er₂Co₁₇ , and Y₂Co₁₇ are reported. Two distinct values mere detected for the samarium compound at low temperature, as a result of the occurrence of in-plane magnetocrystalline anisotropy. From this data it was possible to derive the value of the sixth order anisotropy constant K₃'. However the crystal field model predicts zero value for the sixth-order anisotropy term if only the ground multiplet of the Sm³⁺ ion is considered. This contradiction between theory and experiment was removed by taking into account the mixing of the lowest spin-orbit multiplets of Sm³⁺ due to the exchange interaction. In this frame it was shown that a linear proportionality relation between K₃' and the sixth-order crystal field parameter B₆₆ is valid. This made possible a direct evaluation of B₆₆ from the experimental data. The influence of J mixing on the second-order anisotropy constant K₁ for Sm₂Co₁₇ and Er₂Co₁₇ was also investigated by analyzing the curve H_A(T) in the temperature range T>200 K