Phase transitions in two sublattice Ising systems

A two sublattice Ising systemis ionvestigated by the mean field (MF) and the renormalization group (RG) methods. The properties of the phases and the phase transitions are considered in details for the general case of nonequivalent sublattices. The MF analysis is performed by an expansion in powers of a suitable small parameter. The RG is used to establish the possibility for a fluctuation change of the order of the phase transitions to ferro- and antiferromagnetic states in systems with equivalent sublattices. It is shown that such systems exhibit fluctuation-induced weakly-first-order phase transitions. The RG investigation of systems with nonequivalent sublattices is also presented.