Disrupted chimera ordering of magnetization within FeCl2 layers

Abstract

As a follow-up to a recent report about chimera ordering in Monte Carlo simulations of a three-dimensional Ising spin model (Singh R. et al., EPL, 95 (2011) 10004), further simulations are performed to ascertain the validity and the applicability of the initial results. In the initial work only nearest-neighbour interactions were considered within a cubic lattice of spins, having ferromagnetic interaction between spins within the same plane and anti-ferromagnetic interaction between spins in adjacent planes. This model was proposed as a prototype for certain layered magnetic systems, such as FeCl2. In the present work two main deficiencies in the initial work are addressed. First, use is made of parallel tempering to explore whether or not the reported chimera ordering could be a simulation artefact. This step is important because it is well known that, at lower temperatures, Monte Carlo simulations can often become trapped in local minima of the energy landscape. Furthermore, in the case of frustrated systems, such as the one that was considered, the energy landscape is well known to be complicated, typically containing many local minima. Second, the initial model of a cubic lattice of spins is extended to the face-centred cubic structure for FeCl2. Our extended model, consisting of the frustrated 3-dimensional face-centred cubic lattice of Ising spins, has the correct coupling topology and known exchange interactions for FeCl2. We find that the chimera ordering is robust to the parallel tempering and that it is influenced by the boundary conditions and the number of layers in the fcc lattice. In general one can expect to find small disruptions in the chimera ordering of the magnetization within different layers.