Inverse freezing in a cluster Ising spin-glass model with antiferromagnetic interactions

摘要

Inverse freezing is analyzed in a cluster spin-glass (SG) model that considers infinite-range disordered interactionsnbetween magnetic moments of different clusters (intercluster interaction) and short-range antiferromagneticncoupling J1 between Ising spins of the same cluster (intracluster interaction). The intercluster disorder J isntreated within a mean-field theory by using a framework of one-step replica symmetry breaking. The effectivenmodel obtained by this treatment is computed by means of an exact diagonalization method. With the resultsnwe build phase diagrams of temperature T/J versus J1/J for several sizes of clusters ns (number of spins innthe cluster). The phase diagrams show a second-order transition from the paramagnetic phase to the SG order atnthe freezing temperature Tf when J1/J is small. The increase in J1/J can then destroy the SG phase. It decreasesnTf /J and introduces a first-order transition. In addition, inverse freezing can arise at a certain range of J1/J andnlarge enough ns . Therefore, the nontrivial frustration generated by disorder and short-range antiferromagneticncoupling can introduce inverse freezing spontaneously.