Spin-Lattice coupling on the two dimensional Ising Model

S. A. GRIGERA; L. PILI

Bariloche

Congreso; Exploratory Workshop on Condensed Matter Physics; 2017

CNEA - Balseiro - Max Planck Society

The Ising model is, without a doubt, the most studied magnetic model for insulating solids. One of its most salient features is that it has an exact solution for one and two dimensions. Despite this, the richness of behaviours and phases on real materials has lead people to consider more complex models which take into account, for example, dipolar interactions or lattice distortions. The latter has been the subject of extensive work over the last years and several extensions to the Ising model have been proposed that describe the coupling between elastic and magnetic degrees of freedom. In most of this work, the methodology has been to integrate out the elastic degrees of freedom in order to obtain a simpler effective Hamiltonian, written solely in terms of spin degrees of freedom. Onedrawback from this methodology is that it does not allow one to obtain information about the lattice distortion or to account for magnetic scenarios occurring after a possible structural phase transitions.In this work we consider a simple Ising magnetic model in two dimensions over a square lattice with Einstein-like distortions and do a Monte Carlo simulation that takes into account both degrees of freedom simultaneously. We find that at above a certain degree of coupling between the two degrees of freedom, the system undergoes a simultaneous structural and magnetic transition into a ?checkerboard like? phase. We have studied additional implications of this instability.