Crystal field effects on the saturation magnetic moment of Sm³⁺ ion in ferronagnetic samarium compounds

Abstract

The effects of cubic crystal fields on the saturation magnetic moment of Sm³⁺ ion in ferromagnetic compounds have been investigated. In samarium compounds with magnetic elements, the exchange field H_ex acting on Sm³⁺ ion is taken to be proportional to the sublattice magnetization of the magnetic element, while in compounds with nonmagnetic elements H_ex is taken to be proportional to the spin average of the Sm³⁺ ion and is determined self-consistently. In both types of compounds H_ex is assumed to be along [001] direction. The saturation magnetic moment is calculated by taking into account the admixture of excited (J=7/2 and J=9/2) levels into the ground (J=5/2) level of Sm³⁺ ion by crystal fields and exchange fields. It is shown that depending upon the strength, the crystal fields quench or enhance the magnetic moment from the free ion value, and in some cases force Sm³⁺ ion to behave effectively like an (L+S) ion rather than an (L-S) ion. The crystal fields may have important bearing on the performance of samarium compounds as permanent magnet materials.