The ferrimagnetic mixed spin 1/2 and spin 1 Ising system

A cluster variational theory, within pair approximation, of the mixed spin 1/2-spin 1 ferrimagnet with single-ion anisotropy, is presented. General ex pressions for the Curie temperature and the tricritical point are obtained. The first-order transitions are located from a free energy analysis. The t hermal dependence of the magnetization is studied, and the existence and de pendence of a compensation point on single-ion anisotropy strength is inves tigated for different lattice coordination numbers. Results of the theory a re compared with those of other approximate methods, and with the exact res ults that are available in the case of the honeycomb lattice. (C) 1999 Else vier Science B.V. All rights reserved.