Extended reduced s-d model with anisotropic interactions

An anisotropic generalization of the reduced s-d model with antiferromagnet ically coupled impurities is proposed. This extension consists in introduci ng different coupling constants of s-d interaction and interimpurity coupli ng 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 thermod ynamic limit to the corresponding mean-field Hamiltonian. Equations for the mean-field parameters are derived. The discussion of the possible solution s of these equations is carried out. The predictions of the AERs-dM are com pared with experimental data for magnetization of uranium Kondo compounds U AsS, UAsSe, as function of external magnetic field and temperature. Appropr iate adjustment of the parameters of the model allows the theory to reprodu ce basic features of the substances discussed, viz., c-axis oriented sponta neous magnetization of the system which does not change significantly even in strong external magnetic held perpendicular to this axis. (C) 2001 Elsev ier Science B.V. All rights reserved.