An analysis of the rare earth contribution to the magnetic anisotropy in RCo5 and R2Co17 compounds

An attempt has been made to treat the rare earth contribution to the magnetocrystalline anisotropy in RCo5 and R2Co17 compounds with a single ion model using a Hamiltonian of the form: H=B20O20+gμBJ·HexHex is regarded as arising mainly from the cobalt sublattice. Eigenvalues and eigenfunctions for the above Hamiltonian were obtained when the exchange field is perpendicular to the c-axis and compared with those when it is parallel to the c-axis. For values of Hex estimated from experiment it is found that the sign of B20 determines the direction preference of the rare earth sublattice magnetization. Comparison of theory with experiment shows that the correct sign of B20 can be predicted on the point charge model considering only the effect of rare earth nearest neighbors. The calculations also predict that the quantity |K1R(0) + K2R(0)| is nearly equal to the crystal field overall splitting (CFOAS) determined in the absence of exchange and is independent of the magnitude of the exchange field, provided that the exchange field is sufficiently large. The temperature dependence of |K1R + K2R| has also been calculated and found to agree semiquantitatively with available experimental results.