Half-metallic Ferrimagnetism Driven by Coulomb Enhanced Spin-Orbit Coupling in PdCrO3

TL;DR

This study predicts that Coulomb interactions and spin-orbit coupling in PdCrO$_3$ induce a transition from compensated half-metallic ferrimagnetism to a stable half-metallic ferrimagnet, highlighting the role of Coulomb-enhanced SOC.

Contribution

It introduces a theoretical prediction of Coulomb-enhanced spin-orbit coupling leading to half-metallic ferrimagnetism in PdCrO$_3$, an as-yet-unsynthesized compound.

Findings

Coulomb interactions compensate Cr spin with Pd and oxygen moments.

SOC enhancement leads to large orbital moments on Pd.

Half-metallicity persists despite SOC enhancement.

Abstract

Recently, in the seemingly narrow gap insulating NiCrO$_3$ with the trigonally distorted (R-3c) perovskite-like structure, a compensated half-metal (CHM) is predicted, as applying a modest pressure. Using ab initio calculations including both Coulomb correlations and spin-orbit coupling (SOC), we investigate the as-yet-unsynthesized PdCrO$_3$, isostructural and isovalent to NiCrO$_3$. Upon applying the on-site Coulomb repulsion $U$ to both Pd and Cr ions, the Cr spin moment is precisely compensated with the antialigned spin moments of Pd and oxygens. Coincidentally only one spin channel remains metallic due to the twice larger width of the Pd 4d bands than the Ni 3d bands in NiCrO$_3$, indicating CHM in ambient pressure. Inclusion of SOC as well as correlation effects (LDA+U+SOC) produces a SOC constant enhanced twice over the value of LDA+SOC, leading to unusually large orbital moment of --0.25 $\mu_B$ on Pd. However, the half-metallicity still survives, so that a transition of CHM to a half-metallic ferrimagnet occurs due to Coulomb enhanced SOC. On the other hand, an isovalent, but presumed cubic double perovskite La$_2$PdCrO$_6$ is expected to be a half-metal ferromagnet with tiny orbital moments.