Eur. Phys. J. B (2015) 88: 148
https://doi.org/10.1140/epjb/e2015-60170-x

Regular Article

Magnetic order in the two-dimensional compass-Heisenberg model

¹ Joint Institute for Nuclear Research, 141980 Dubna, Russia
² Institut für Theoretische Physik, Universität Leipzig, 04109 Leipzig, Germany

^a e-mail: plakida@theor.jinr.ru

Received: 4 March 2015
Received in final form: 28 April 2015
Published online: 8 June 2015

Abstract

A Green-function theory for the dynamic spin susceptibility in the square-lattice spin-1/2 antiferromagnetic compass-Heisenberg model employing a generalized mean-field approximation is presented. The theory describes magnetic long-range order (LRO) and short-range order (SRO) at arbitrary temperatures. The magnetization, Néel temperature T_N, specific heat, and uniform static spin susceptibility χ are calculated self-consistently. As the main result, we obtain LRO at finite temperatures in two dimensions, where the dependence of T_N on the compass-model interaction is studied. We find that T_N is close to the experimental value for Ba₂IrO₄. The effects of SRO are discussed in relation to the temperature dependence of χ.