Effect of crystal-field anisotropy on the magnetization of a spin pair within various decoupling schemes

The Green's function theory for a Heisenberg Hamiltonian with exchange parameter plus a single-ion anisotropy term is applied to a system of two spins S = 1. In order to assess the accuracy of the various decoupling schemes of the Green's functions, which involve products of operators at the same site, the magnetization of a spin pair is calculated within various decoupling procedures, and the results compared with exact solutions. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)