Ab initio study of the CE magnetic phase in half-doped manganites: Purely magnetic versus double exchange description

TL;DR

This study uses ab initio calculations to analyze the electronic interactions in the CE magnetic phase of half-doped manganites, comparing magnetic and double exchange models to accurately describe their local physics.

Contribution

It introduces a refined double exchange model involving excited non-Hund states that accurately reproduces the ab initio spectra and local potential energy curves.

Findings

Double exchange configurations dominate low-energy states.

The refined double exchange model outperforms the Heisenberg model.

The model accurately reproduces the local potential energy curves.

Abstract

The leading electronic interactions governing the local physics of the CE phase of half-doped manganites are extracted from correlated ab initio calculations performed on an embedded cluster. The electronic structure of the low-energy states is dominated by double exchange configurations and O-2$p_{\sigma}$ to Mn-3d charge transfer configurations. The model spectra of both a purely magnetic non-symmetric Heisenberg Hamiltonian involving a magnetic oxygen and two non-symmetric double exchange models are compared to the \textit{ab initio} one. While a satisfactory agreement between the Heisenberg spectrum and the calculated one is obtained, the best description is provided by a double exchange model involving excited non-Hund atomic states. This refined model not only perfectly reproduces the spectrum of the embedded cluster in the crystal geometry, but also gives a full description of the local double-well potential energy curve of the ground state (resulting from the interaction of the charge localized electronic configurations) and the local potential energy curves of all excited states ruled by the double exchange mechanism.