Ground-state phase diagrams of Ising metamagnet in a mixed longitudinal and transverse magnetic field

The ground-state magnetic properties of a two-sublattice Ising metamagnet in a mixed longitudinal and transverse magnetic field are studied within the effective-field theory. A parameter j(2) = J(2)/J(1) is introduced, which reflects the strength ratio of spin coupling between adjacent planes and in each plane. In addition to the second-order transition lines, the first-order transition lines are also presented, since the ground-state energy can be calculated numerically. The ground-state phase diagrams in h(x)-h(z) are presented. The results show that when j(2) <0 the phase transition of the system is always first-order for h(x) < 2.751, and when -1000 <= j(2)<0 it is always second-order for h(x) > 4.36. For the given h(x) (0<h(x)<14.71), the longitudinal critical magnetic field increases as j(2) decreases. The reentrant phenomenon occurs in the range of j2 < -11.89, h(x) > 14.71. There is no fourth-order critical point in the phase diagrams given by using EFT as found by using mean field theory (MFT). (C) 2008 Elsevier B. V. All rights reserved.