Metamagnetic transitions in an Ising antiferromagnet

An Ising antiferromagnet of arbitrary spin is examined in the molecular field approximation. It is found that the field induced transition can be of four different types: second order, first order, a first order followed by a second order and two successive first order, depending on the temperature and the ratio of the nn to nnn exchange interactions. Landau's theory of second order phase transition in conjunction with a detailed examination of the behavior of the free energy is employed to map the regions of the different types of transition.