Easy-plane multi-$\mathbf{q}$ magnetic ground state of Na$_3$Co$_2$SbO$_6$

TL;DR

This study reveals that Na$_3$Co$_2$SbO$_6$ maintains a multi-$ extbf{q}$ magnetic ground state despite structural anisotropy, highlighting the robustness of complex magnetic orders driven by higher-order interactions in honeycomb cobaltates.

Contribution

It demonstrates that Na$_3$Co$_2$SbO$_6$ exhibits a multi-$ extbf{q}$ magnetic ground state, influenced by higher-order interactions, contrasting with simpler models like the Kitaev framework.

Findings

The ground state remains multi-$ extbf{q}$ despite structural anisotropy.

Ordered moments are entirely in-plane and orthogonal to propagation vectors.

The ground state supports an XXZ easy-plane anisotropic model over a Kitaev model.

Abstract

Na$_3$Co$_2$SbO$_6$ is a potential Kitaev magnet with a monoclinic layered crystal structure. Recent investigations of the $C_3$-symmetric sister compound Na$_2$Co$_2$TeO$_6$ have uncovered a unique triple-$\mathbf{q}$ magnetic ground state, as opposed to a single-$\mathbf{q}$ (zigzag) one, prompting us to examine the influence of the reduced structural symmetry of Na$_3$Co$_2$SbO$_6$ on its ground state. Neutron diffraction data obtained on a twin-free crystal reveal that the ground state remains a multi-$\mathbf{q}$ state, despite the system's strong in-plane anisotropy. This robustness of multi-$\mathbf{q}$ orders suggests that they are driven by a common mechanism in the honeycomb cobaltates, such as higher-order magnetic interactions. Spin-polarized neutron diffraction results show that the ordered moments are entirely in-plane, with each staggered component orthogonal to the propagating wave vector. The inferred ground state favors a so-called XXZ easy-plane anisotropic starting point for the microscopic model over a Kitaev one, and features unequal ordered moments reduced by strong quantum fluctuations.