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Study of the first-order transition in the spin-1 Blume–Capel model by using effective-field theory

2012; Elsevier BV; Volume: 376; Issue: 45 Linguagem: Inglês

10.1016/j.physleta.2012.09.003

1873-2429

Emanuel Costabile, Marcio A. Amazonas, J. Roberto Viana, J. Ricardo de Sousa,

Material Dynamics and Properties

The spin-1 Blume–Capel model on a square lattice is studied by using an effective-field theory (EFT) with correlation. We propose an expression for the free energy within the EFT. The phase diagram is constructed in the temperature (T) and single-ion anisotropy amplitude (D) plane. The first-order transition line is obtained by Maxwell construction (comparison between free energies). Our results predict first-order transitions at low temperatures and large anisotropy strengths, which correspond in the phase diagram to the existence of a tricritical point (TCP). We compare our results with mean-field approximation (MFA), that show a qualitative correct behavior for the phase diagram.