Phase diagram of an Ising model for ultrathin magnetic films: Comparing mean field and Monte Carlo predictions

SANTIAGO A. PIGHÍN; SERGIO A. CANNAS

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Año: 2007 vol. 75 p. 1 - 9

0163-1829

   We study the critical properties of a two-dimensional Ising model with competing ferromagnetic exchangeand dipolar interactions, which models an ultrathin magnetic film with high out-of-plane anisotropy in themonolayer limit. In this work, we present a detailed calculation of the (d,T) phase diagram, d being the ratiobetween exchange and dipolar interaction intensities. We compare the results of both mean field approximationand Monte Carlo numerical simulations in the region of low values of d, identifying the presence of a recentlydetected phase with nematic order in different parts of the phase diagram, besides the well-known striped andtetragonal liquid phases. We also found that, in the regions of the phase diagram where Monte Carlo simula-tions display nematic order, the mean field approximation predicts hybrid solutions composed by stripes ofdifferent widths. Another remarkable qualitative difference between both calculations is the absence, in thisregion of the Monte Carlo phase diagram, of the temperature dependency of the equilibrium stripe widthpredicted by the mean field approximation.