Spin-orbit coupled j=1/2 iridium moments on the geometrically frustrated fcc lattice

TL;DR

This study investigates the magnetic properties of spin-orbit coupled iridium moments on a frustrated face-centered cubic lattice, revealing complex magnetic orders and emphasizing the dominant role of Kitaev exchange in related materials.

Contribution

It provides a comprehensive analysis of possible magnetic orders in iridates with spin-orbit coupling on a fcc lattice, highlighting the significance of Kitaev interactions and explaining experimental observations.

Findings

Multiple magnetic orders including antiferromagnetism and spirals identified.

Kitaev exchange is dominant in the studied iridates.

Explanation for differing magnetic behaviors in La2ZnIrO6 and La2MgIrO6.

Abstract

Motivated by experiments on the double perovskites La2ZnIrO6 and La2MgIrO6, we study the magnetism of spin-orbit coupled j=1/2 iridium moments on the three-dimensional, geometrically frustrated, face-centered cubic lattice. The symmetry-allowed nearest-neighbor interaction includes Heisenberg, Kitaev, and symmetric off-diagonal exchange. A Luttinger-Tisza analysis shows a rich variety of orders, including collinear A-type antiferromagnetism, stripe order with moments along the [111]-direction, and incommensurate non-coplanar spirals, and we use Monte Carlo simulations to determine their magnetic ordering temperatures. We argue that existing thermodynamic data on these iridates underscores the presence of a dominant Kitaev exchange, and also suggest a resolution to the puzzle of why La2ZnIrO6 exhibits `weak' ferromagnetism, but La2MgIrO6 does not.