Long range magnetic ordering in Na$_2$IrO$_3$

TL;DR

This study combines experimental and theoretical methods to reveal three-dimensional antiferromagnetic order with a zig-zag spin structure in Na$_2$IrO$_3$, a candidate for a gapless spin-liquid, below 13.3 K.

Contribution

It provides the first detailed magnetic structure determination of Na$_2$IrO$_3$ using resonant x-ray scattering and first principles calculations, proposing a novel zig-zag spin arrangement.

Findings

Na$_2$IrO$_3$ exhibits 3D long-range antiferromagnetic order below 13.3 K.

The magnetic moments are mainly aligned along the a-axis.

The proposed spin structure is a novel zig-zag configuration.

Abstract

We report a combined experimental and theoretical investigation of the magnetic structure of the honeycomb lattice magnet Na$_2$IrO$_3$, a strong candidate for a realization of a gapless spin-liquid. Using resonant x-ray magnetic scattering at the Ir L$_3$-edge, we find 3D long range antiferromagnetic order below T$_N$=13.3 K. From the azimuthal dependence of the magnetic Bragg peak, the ordered moment is determined to be predominantly along the {\it a}-axis. Combining the experimental data with first principles calculations, we propose that the most likely spin structure is a novel "zig-zag" structure.