Phase diagram and phase separation of cuprate oxides in decorated Ising model

Abstract

In application to lanthanum cuprates the Ising model with random antiferromagnetic (AF) and ferromagnetic (FM) interactions between Cu atoms in CuO 2 layers is investigated by the mean-field approximation. The effective interaction between holes as well as their participation in a formation of the intermediate oxygen valency of CuO 2 layer are taken into account. In the phase diagram temperature–hole concentration which exhibits a range of phase separation and contains the critical point AF phase with low hole concentration, AF phase with rich hole concentration is found. Depending on doping level the suggested model describes both the absence of phase separation and the separation into paramagnetic (PM)–AF, PM–FM, and AF–FM phases.