The general-spin Blume-Capel model: A study of the multicritical behavior using effective-field theory

The general-spin Blume-Capel model is studied by using an effective-field theory with correlation. An expression for the free energy within the effective-field theory is proposed, and the complete phase diagram is constructed in the temperature and single-ion anisotropy plane. The first-order transition lines are obtained by Maxwell construction (comparison between free energies). Beyond first-order transitions at low temperatures, the results show second-order transitions and tricritical points, as well as a variety of double critical endpoints. The existence of the tricritical point and the number of critical endpoints strongly depend on the value of the spin. (C) 2013 Elsevier B.V. All rights reserved.