Re-entrant ferromagnetism in diluted two-dimensional Ising models with competitive nearest- and next-nearest-neighbour interactions

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Abstract
Using the finite-cluster approximation, phase diagrams of bond- and site-diluted two-dimensional square-lattice Ising models with competitive nearest-neighbour (NN) and exhibit tricritical points for -0.238< alpha <0( alpha being the ratio of NNN to NN interactions) and re-entrant ferromagnetism for -0.173< alpha <0 in the case of bond dilution. For site dilution, tricritical points are found for -0.238< alpha <0 and re-entrant ferromagnetism for -0.182< alpha <0. These results indicate that re-entrant behaviour seems to be a characteristic feature of systems in which frustration and disorder are present.