Orbital Polarization and Fluctuation in Manganese Oxides

TL;DR

This paper investigates the role of orbital polarization and fluctuations in manganese oxides using an extended Hubbard model, revealing their importance in magnetic phases and colossal magnetoresistance phenomena.

Contribution

It introduces a comprehensive meanfield and RPA analysis of orbital effects across doping levels, highlighting the significance of orbital polarization and fluctuations.

Findings

Large orbital polarization is crucial for magnetic phase reproduction.

Orbital fluctuations are significant in the ferromagnetic metallic region.

Spin wave softening occurs near the zone boundary.

Abstract

In a form which include the mother compound, we studied the extended Hubbard-type model with the orbital degeneracy for any doping concentration. Meanfield phase diagram and the spin wave excitation in RPA are calculated. It turned out that a large orbital polarization is essential to reproduce the magnetic phases depending on the doping concentration. Base on this result, we discuss the spin canting, the spin wave dispersion, and spin wave stiffness from the standing point of the large orbital polarization. We also discuss the orbital fluctuation which turned out to be important in the ferromagnetic metallic region where the CMR is observed. Spin wave softening near the zone boundary is also discussed in this context.