Manganites at Low Temperatures and Light Doping:Band Approach and Percolation

TL;DR

This paper models low-temperature, lightly doped manganites using a band approach combined with percolation theory, revealing how Hund's coupling and Jahn-Teller effects influence magnetic and electronic phase transitions.

Contribution

It introduces a combined band and percolation model to explain magnetic ordering and phase transitions in manganites at low temperatures and light doping levels.

Findings

LaMnO₃ is a band insulator with 2D ferromagnetic layers.

Critical doping concentration for metallic behavior is approximately 0.16.

Percolation theory describes the phase transition to ferromagnetism and metallicity.

Abstract

A tight-band model is employed for the $e_{2g}$-orbitals in manganites. It is shown that a large intraatomic Hund's coupling, $J_H$ and the resulting double-exchange mechanism lead to antiferromagnetic ordering along one of the cubic axis stabilized by the cooperative JT effect which further decreases the band energy of electrons. As a result, LaMnO$_3$ is a band insulator built of 2D ferromagnetic layers. The critical concentration $x_c\simeq 0.16$, for onset of ferromagnetic and metallic behavior at low temperatures in La$_{1-x}$Sr$_x$MnO$_3$ and the phase transition are treated in the percolation approach.