title: Phase transitions in the two-dimensional superantiferromagnetic Ising model with next-nearest-neighbor interactions.
abstract: We use Monte Carlo and transfer matrix methods in combination with extrapolation schemes to determine the phase diagram of the two-dimensional superantiferromagnetic (SAF) Ising model with next-nearest-neighbor (NNN) interactions in a magnetic field. The interactions between nearest-neighbor (NN) spins are ferromagnetic along x, and antiferromagnetic along Y. We find that for sufficiently low temperatures and fields, there exists a region limited by a critical line of second-order transitions separating a SAF phase from a magnetically induced paramagnetic phase. We did not find any region with either first-order transition or with reentrant behavior. The NNN couplings produce either an expansion or a contraction of the SAF phase. Expansion occurs when the interactions are antiferromagnetic, and contraction when they are ferromagnetic. There is a critical ratio R(c)=1/2 between NNN and NN couplings, beyond which the SAF phase no longer exists.
authors.affiliation: Departamento de Física, Universidade Federal Fluminense, Avenida Litorânea s/n, Niterói, 24210-340, Rio de Janeiro, Brazil. amen@if.uff.br
authors.forename: A
authors.initials: A
authors.lastname: Saguia
authors.forename: B
authors.initials: B
authors.lastname: Boechat
authors.forename: J
authors.initials: J
authors.lastname: Florencio
authors.forename: O F
authors.initials: OF
authors.lastname: de Alcantara Bonfim
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D060526:Magnetic Fields; D015233:Models, Statistical; D009010:Monte Carlo Method; D044367:Phase Transition