Ferromagnetic Polarons in La0.5Ca0.5MnO3 and La0.33Ca0.67MnO3

TL;DR

This study uses Hartree-Fock calculations to reveal that La0.5Ca0.5MnO3 and La0.33Ca0.67MnO3 have magnetic ground states composed of ordered ferromagnetic polarons, aligning with recent experimental observations.

Contribution

It demonstrates the polaronic magnetic structure in these compounds, supporting the Zener polaron model with detailed electronic and magnetic properties.

Findings

Polarons form herring-bone patterns with strong intra-polaron coupling.

Each polaron has a net magnetic moment of 7.0 Bohr magnetons.

Magnetic moments on Mn ions are approximately 3.8-3.9 Bohr magnetons.

Abstract

Unrestricted Hartree-Fock calculations on La0.5Ca0.5MnO3 and La0.33Ca0.67MnO3 in the full magnetic unit cell show that the magnetic ground states of these compounds consist of 'ferromagnetic molecules' or polarons ordered in herring-bone patterns. Each polaron consists of either three or five Mn ions separated by O- ions with a magnetic moment opposed to those of the Mn ions. Ferromagnetic coupling within the polarons is strong while coupling between them is relatively weak. Magnetic moments on the Mn ions range between 3.8 and 3.9 Bohr magnetons in La0.5Ca0.5MnO3 and moments on the O- ions are -0.7 Bohr magnetons. Each polaron has a net magnetic moment of 7.0 Bohr magnetons, in good agreement with recently reported magnetisation measurements from electron microscopy. The polaronic nature of the electronic structure reported here is obviously related to the Zener polaron model recently proposed for Pr0.6Ca0.4MnO3 on the basis of neutron scattering data.