Multicritical behavior of the two-dimensional transverse Ising metamagnet in a longitudinal magnetic field

Magnetic phenomena of the two-dimensional anisotropic antiferromagnetic Ising model in both uniform longitudinal (H) and uniform transverse (Omega) magnetic fields are studied by employing a mean-field variational approach based on Bogoliubov inequality for the free energy. The phase diagrams in the magnetic fields and temperature (T) planes, namely H - T and Omega - T, are analyzed on an anisotropic square lattice for some values of the ratio alpha = J(y)/J(x), where J(x) and J(y) are, respectively, the exchange interactions along the x and y directions. Depending on the range of the Hamiltonian parameters, one has only second-order transition lines, only first-order transition lines, or both first- and second-order transition lines with the presence of tricritical points. In addition, the corresponding phase diagrams are free from any reentrant behavior. (C) 2017 Elsevier B.V. All rights reserved.