Double exchange and orbital correlations in electron-doped manganites

TL;DR

This study uses a double exchange model with orbital interactions to explain phase diagrams and orbital ordering in electron-doped manganites, showing Jahn-Teller effects are less influential in certain doping regimes.

Contribution

It demonstrates that a double exchange model with orbital interactions can accurately reproduce phase diagrams and orbital orderings without heavily relying on Jahn-Teller effects.

Findings

The model reproduces observed phase diagrams and orbital ordering.

Inclusion of interactions stabilizes the C-phase and shifts phase boundaries.

Jahn-Teller effects are less significant for x>0.5 in electron-doped manganites.

Abstract

A double exchange model for degenerate $e_g$ orbitals with intra- and inter-orbital interactions has been studied for the electron doped manganites A$_{1-x}$B$_{x}$MnO$_3$ ($x > 0.5$). We show that such a model reproduces the observed phase diagram and orbital ordering in the intermediate bandwidth regime and the Jahn-Teller effect, considered to be crucial for the region $x<0.5$, does not play a major role in this region. Brink and Khomskii have already pointed this out and stressed the relevance of the anistropic hopping across the degenerate $e_g$ orbitals in the infinite Hund's coupling limit. From a more realistic calculation with finite Hund's coupling, we show that inclusion of interactions stabilizes the C-phase, the antiferromagnetic metallic A-phase moves closer to $x=0.5$ while the ferromagnetic phase shrinks. This is in agreement with the recent observations of Kajimoto et. al. and Akimoto et. al.