Spiral order in the honeycomb iridate Li2IrO3

TL;DR

This paper explains the incommensurate spiral magnetic order in Li2IrO3 using an extended Heisenberg-Kitaev model, aligning with experimental observations and highlighting the role of second-neighbor interactions.

Contribution

It introduces an extended Heisenberg-Kitaev model that accounts for the spiral order in Li2IrO3, incorporating second-neighbor exchanges and matching experimental data.

Findings

The magnetic susceptibility peak is within the first Brillouin zone.

The Curie-Weiss temperature is negative, indicating antiferromagnetic fluctuations.

Second-neighbor spin-exchange significantly influences magnetic order.

Abstract

The honeycomb iridates A2IrO3 (A=Na, Li) constitute promising candidate materials to realize the Heisenberg-Kitaev model (HKM) in nature, hosting unconventional magnetic as well as spin liquid phases. Recent experiments suggest, however, that Li2IrO3 exhibits a magnetically ordered state of incommensurate spiral type which has not been identified in the HKM. We show that these findings can be understood in the context of an extended Heisenberg-Kitaev scenario satisfying all tentative experimental evidence: (i) the maximum of the magnetic susceptibility is located inside the first Brillouin zone, (ii) the Curie-Weiss temperature is negative relating to dominant antiferromagnetic fluctuations, and (iii) significant second-neighbor spin-exchange is involved.