Anisotropic Multi-Q Order in CoxTaS2

TL;DR

This study uncovers an anisotropic (2+1)Q magnetic phase in Co$_x$TaS$_2$ with complex spin structures and anomalous Hall effects, advancing understanding of multi-Q magnetic states in transition metal dichalcogenides.

Contribution

It identifies and characterizes an anisotropic (2+1)Q magnetic phase in Co$_x$TaS$_2$, revealing a new class of multi-Q states with scalar spin chirality.

Findings

Discovery of anomalous magneto-birefringence in Co$_x$TaS$_2$

Identification of the (2+1)Q magnetic phase with distinct symmetry properties

Correlation between magnetic structure and anomalous Hall effect

Abstract

The cobalt-intercalated transition metal dichalcogenide Co$_x$TaS$_2$ hosts a rich landscape of magnetic phases that depend sensitively on $x$. While the stoichiometric compound with $x=1/3$ exhibits a single magnetic transition, samples with $x\leq 0.325$ display two transitions with an anomalous Hall effect (AHE) emerging in the lower temperature phase. Here, we resolve the spin structure in each phase by employing a suite of magneto-optical probes that include the discovery of anomalous magneto-birefringence -- a spontaneous time-reversal sensitive rotation of the principal optic axes. A symmetry-based analysis identifies the AHE-active phase as an anisotropic (2+1)\textbf{Q} state, in which magnetic modulation at one wavevector (\textbf{Q}) differs in symmetry from that at the remaining two. The (2+1)\textbf{Q} state naturally exhibits scalar spin chirality as a mechanism for the AHE and expands the classification of multi-Q magnetic phases.