Magnetic order in the two-dimensional compass-Heisenberg model

TL;DR

This paper develops a Green-function theory for the 2D compass-Heisenberg model, capturing magnetic order and thermodynamic properties, and finds a finite Néel temperature consistent with experiments on Ba2IrO4.

Contribution

It introduces a generalized mean-field Green-function approach to analyze magnetic order in the 2D compass-Heisenberg model at finite temperatures.

Findings

Finite Néel temperature T_N close to experimental value for Ba2IrO4

The theory describes both long-range and short-range magnetic order

Temperature dependence of spin susceptibility is explained

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, N'eel temperature T_N, specific heat, and uniform static spin susceptibility $\chi$ 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 $\chi$.