First principles study of the spin state transitions in GdBaCo$_2$O$_{5.5}$

TL;DR

This study uses first principles calculations to explore how the spin state of Co$^{3+}$ ions affects the electronic structure and orbital ordering in GdBaCo$_2$O$_{5.5}$, predicting anisotropy and orbital moments.

Contribution

It provides a detailed first-principles analysis of spin state transitions, orbital ordering, and anisotropy in GdBaCo$_2$O$_{5.5}$, including predictions of magnetic properties.

Findings

Insulating phases are characterized and scenarios for metallic states are proposed.

Orbital ordering is identified and its electronic origin is explained.

Unquenched orbital angular momenta are calculated and their origins are described.

Abstract

Electronic structure calculations were carried out on the compound GdBaCo$_2$O$_{5.5}$. The electronic structure variation with a change in the spin state of the Co$^{3+}$ ion in an octahedral environment has been studied. All the insulating phases are described and possible scenarios for the metallic ones are presented. Orbital ordering is shown to take place and the electronic structure leading to it is determined. The Ising-like anisotropy shown experimentally can be predicted. Also, big unquenched orbital angular momenta are calculated and their origin is described.