Robust triple-q magnetic order with trainable spin vorticity in Na$_2$Co$_2$TeO$_6$

TL;DR

This paper investigates the unique triple-q magnetic order in Na$_2$Co$_2$TeO$_6$, demonstrating its insensitivity to certain strains and its ability to generate trainable fictitious magnetic fields via spin vorticity.

Contribution

It provides experimental evidence supporting the existence of triple-q magnetic order and its distinctive properties, advancing understanding of Kitaev magnets.

Findings

Triple-q order is unaffected by in-plane uniaxial strains.

Large Faraday rotations indicate spin vorticity in the ordered state.

Fictitious magnetic fields can be trained via ferrimagnetic moments.

Abstract

Recent studies suggest that the candidate Kitaev magnet Na$_2$Co$_2$TeO$_6$ possesses novel triple-$\mathbf{q}$ magnetic order instead of conventional single-$\mathbf{q}$ zigzag order. Here we present dedicated experiments in search for distinct properties expected of the triple-$\mathbf{q}$ order, namely, insensitivity of the magnetic domains to weak $C_3$ symmetry-breaking fields and fictitious magnetic fields generated by the spin vorticity. In structurally pristine single crystals, we show that $C_3$ symmetry-breaking in-plane uniaxial strains do not affect the order's magnetic neutron diffraction signals. We further show that $\mathbf{c}$-axis propagating light exhibits large Faraday rotations in the ordered state due to the spin vorticity, the sign of which can be trained via the system's ferrimagnetic moment. These results are in favor of the triple-$\mathbf{q}$ order in Na$_2$Co$_2$TeO$_6$ and reveal its unique emerging behavior.