Double exchange and orbital correlations in electron-doped manganites

¹ Department of Physics & Meteorology and Centre for Theoretical Studies Indian Institute of Technology - Kharagpur 721302, India
² Department of Physics & Astronomy, Michigan State University East Lansing, MI 48823-1116, USA

Corresponding authors: tulika@phy.iitkgp.ernet.in, arghya@phy.iitkgp.ernet.in

Received: 14 May 2002
Accepted: 2 July 2002

Abstract

A double-exchange model for degenerate e_g orbitals with intra- and inter-orbital interactions has been studied for the electron-doped manganites _x (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.