The effect of a single-ion anisotropy on the phase diagram of a mixed ferro-ferrimagnetic ternary alloy

The phase diagram of the ABpC1−p mixed ferro-ferrimagnetic ternary alloy consisting of Ising spins sA=1, , and is investigated by the use of a mean-field theory based on the Bogoliubov inequality for the Gibbs free energy. The effect of the single-ion anisotropy on the transition temperature is discussed and topologically different kinds of phase diagrams are achieved by changing values of the parameters in the model Hamiltonian. Besides second-order transitions, lines of first-order transitions terminating either at a tricritical point, or an isolated critical point, are found. The former lines separate ferrimagnetic (or ferromagnetic) and paramagnetic phases, while the latter separate two ordered ferrimagnetic phases within the ordered region.