Study of the ferromagnetic-insulator phase in manganites

TL;DR

This paper investigates the ferromagnetic-insulator phase in manganites, proposing a localized-band model that explains how magnetic polarons form and percolate, leading to ferromagnetic insulating behavior.

Contribution

It introduces a new localized-band model involving intermediate-range electron-electron and electron-phonon interactions to explain ferromagnetic insulators in manganites.

Findings

Magnetic polarons form via double exchange in an antiferromagnetic background.

Percolation of magnetic polarons results in ferromagnetic insulating phase.

Ferromagnetism intensifies with increased doping or dominant hopping energy.

Abstract

Understanding the coexistence of ferromagnetism and insulating behavior in manganites is an unsolved problem. We propose a localized-band model involving effective intermediate-range electron-electron (electron-hole) repulsion (attraction) generated by cooperative electron-phonon interaction. Double exchange mechanism, involving holes virtually hopping to nearest neighbors and back, produces magnetic polarons in an antiferromagnetic environment; when these magnetic polarons coalesce and percolate the system, we get a ferromagnetic insulator. Ferromagnetism gets more pronounced when the holes (doping) increases or when the ratio hopping/polaronic-energy dominates over superexchange-coupling/hopping.