Orbital ordering of Ir-t2g states in the double perovskite Sr2CeIrO6

TL;DR

This study combines experiments and first-principles calculations to reveal orbital ordering, magnetic properties, and the importance of spin-orbit coupling in the double perovskite Sr2CeIrO6, highlighting complex interactions in this geometrically frustrated lattice.

Contribution

It provides the first detailed analysis of orbital ordering and magnetic moments in Sr2CeIrO6, emphasizing the roles of electron correlation and spin-orbit coupling.

Findings

Ir$^{4+}$ exhibits anti-ferro orbital ordering with alternating d$_{yz}$ and d$_{xz}$ orbitals.

The Ir-5d orbital magnetic moment is approximately 1.3 times larger than the spin magnetic moment.

The AFM-insulating ground state requires both electron-electron correlation and spin-orbit coupling.

Abstract

The electronic and magnetic properties of monoclinic double perovskite Sr$_2$CeIrO$_6$ were examined based on both experiments and first-principles density functional theory calculations. From the calculations we conclude that low-spin-state Ir$^{4+}$ (5$\textit{d}^5$, S=$\frac{1}{2}$) shows t$_{2g}$ band derived anti-ferro type orbital ordering implying alternating occupations of $\textit{d}_{yz}$ and $\textit{d}_{xz}$ orbitals at the two symmetrically independent Ir sites. The experimentally determined Jahn-Teller type distorted monoclinic structure is consistent with the proposed orbital ordering picture. Surprisingly, the Ir-5$\textit{d}$ orbital magnetic moment was found to be $\approx$ 1.3 times larger than the spin magnetic moment. The experimentally observed AFM-insulating states are consistent with the calculations. Both electron-electron correlation and spin-orbit coupling (SOC) are required to drive the experimentally observed AFM-insulating ground state. This single active site double perovskite provides a rare platform with a prototype geometrically frustrated fcc lattice where among the different degrees of freedom (i.e spin, orbital, and lattice), spin-orbit interaction and Coulomb correlation energy scales compete and interact with each other.