Temperature effects in a spin-orbital model for manganites

TL;DR

This paper investigates how temperature influences magnetic and orbital correlations in a layered manganite model, revealing the delicate balance between ferromagnetic and antiferromagnetic states and the persistence of orbital order at higher temperatures.

Contribution

It introduces a two-dimensional orbital superexchange model capturing the competition between magnetic orders and their temperature dependence in layered manganites.

Findings

Small parameter changes switch magnetic order.

Spin order is easily destroyed with temperature.

Orbital correlations persist beyond the loss of ferromagnetic order.

Abstract

We study a two-dimensional effective orbital superexchange model derived for strongly correlated e_g electrons coupled to t_{2g} core spins in layered manganites. One finds that the ferromagnetic and antiferromagnetic correlations closely compete, and small changes of parameters can switch the type of magnetic order. For the same reason, spin order is easily destroyed with rising temperature, while alternating orbital correlations can persist to temperatures where FM order has already melted. A scenario for the AF phase observed in LaSrMnO_4 is presented.