High-order J-mixing corrections to the generalized linear theory of magnetic anisotropy

A generalization of the linear theory for J-mixing compounds has recently been reported; this allows to describe the system as an effective isolated multiplet, keeping J-mixing effects into account as second-order perturbative corrections. Within this framework, analytical expressions for the free energy can be obtained. In the present paper the effect of fourth-order J-mixing corrections on the anisotropy is discussed for Sm-based intermetallic alloys, and it is found to be important for magnetic compounds with strong exchange interaction.