Electronic origin of magnetic and orbital ordering in insulating LaMnO_3

TL;DR

This paper develops a comprehensive spin-orbital model for insulating LaMnO_3, explaining its magnetic and orbital ordering through purely electronic mechanisms and accurately predicting transition temperatures and exchange interactions.

Contribution

It introduces a realistic SU(2)-symmetric model including superexchange and Jahn-Teller effects, providing a quantitative explanation of LaMnO_3's magnetic properties.

Findings

Magnetic ordering is stabilized by e_g superexchange alone.

The model quantitatively explains the transition temperature.

It accounts for anisotropic exchange interactions.

Abstract

We derive a spin-orbital model for insulating LaMnO_3 which fulfills the SU(2) symmetry of S=2 spins at Mn^{3+} ions. It includes the complete e_g and t_{2g} superexchange which follows from a realistic Mn^{2+} multiplet structure in cubic site symmetry, and the Jahn-Teller induced orbital interactions. We show that the magnetic ordering observed in LaMnO_3 is stabilized by a purely electronic mechanism due to the e_g-superexchange alone, and provide for the first time a quantitative explanation of the observed transition temperature and the anisotropic exchange interactions.