Temperature effects in a spin-orbital model for manganites

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.