Extended reduced s–d model with anisotropic interactions

An anisotropic generalization of the reduced s–d model with antiferromagnetically coupled impurities is proposed. This extension consists in introducing different coupling constants of s–d interaction and interimpurity coupling for spin components along the c-axis and perpendicular to the c-axis. It is shown that the Hamiltonian of the anisotropic version of the reduced s–d model (AERs–dM), constructed in this manner, is equivalent in the thermodynamic limit to the corresponding mean-field Hamiltonian. Equations for the mean-field parameters are derived. The discussion of the possible solutions of these equations is carried out. The predictions of the AERs–dM are compared with experimental data for magnetization of uranium Kondo compounds UAsS, UAsSe, as function of external magnetic field and temperature. Appropriate adjustment of the parameters of the model allows the theory to reproduce basic features of the substances discussed, viz., c-axis oriented spontaneous magnetization of the system which does not change significantly even in strong external magnetic field perpendicular to this axis