Ising antiferromagnets in a nonzero uniform magnetic field

We evaluate the density of states g(M, E) as a function of energy E and magnetization M of Ising models on square and triangular lattices, using the exact enumeration method for small systems and the Wang-Landau method for larger systems. From the density of states the average magnetization per spin, m(T, h), of the antiferromagnets has been obtained for any values of temperature T and uniform magnetic field h. Also, based on g(M, E), the behaviour of m(T, h) is understood microcanonically. The microcanonical approach reveals the differences between the unfrustrated model (on the square lattice) and the frustrated one (on the triangular lattice).