Eur. Phys. J. B 27, 153-159 (2002)
https://doi.org/10.1140/epjb/e20020140

Landau expansion for a metamagnetic model

¹ Departamento de Física, Universidade Federal de Santa Catarina 88040-900, Florianópolis, SC, Brazil
² Instituto de Física, Universidade de São Paulo, Caixa Postal 66318, 05389-970 Sao Paulo, SP, Brasil

Corresponding author: ^a wagner@fisica.ufsc.br

Received: 28 November 2001
Published online: 15 May 2002

Abstract

We performed a detailed Landau expansion of the free energy for a metamagnetic model considering terms up to twelfth order. We obtained explicit expressions for the coefficients as a function of the temperature and the ratio between ferro- and antiferromagnetic interactions. We showed that a naive analysis based on the signs of these coefficients cannot always give us sufficient guarantee about the correctness of the phase diagram of the model. In these cases it is necessary to resort to the full expression of the free energy in order to characterize the nature of the phase transition.