Evidence for magnetoelastic coupling and chiral magnetic ground state in quasi-van der Waals tr-Cr$_{1.22}$Te$_{2}$

TL;DR

This study uncovers the magnetic structure and evidence of magnetoelastic coupling in quasi-van der Waals tr-Cr$_{1.22}$Te$_{2}$, revealing a chiral magnetic ground state and topological Hall effect through comprehensive experimental analysis.

Contribution

It provides the first detailed magnetic structure of tr-Cr$_{1.22}$Te$_{2}$ and demonstrates the existence of a chiral magnetic ground state linked to topological Hall effect.

Findings

Two magnetic transitions at 197 K and 211 K.

Chiral umbrella-like spin structure with finite spin chirality.

Presence of topological Hall effect due to chiral magnetic order.

Abstract

Trigonal tr-Cr$_{1+\delta}$Te$_{2}$ is a well-known ferromagnetic material that has recently drawn much attention due to the discovery of zero-field skyrmion state, unusual anomalous Hall effect, topological Hall effect, and topological Nernst effect. This quasi-van der Waals (vdW) layered material with intercalated Cr atoms possesses many peculiar features that depend on the amount of Cr intercalation, although the microscopic magnetic ground state is still elusive. We reveal the structural and magnetic properties of tr-Cr$_{1.22}$Te$_{2}$ by low-temperature x-ray diffraction, magnetization, temperature-dependent Raman spectroscopy, and single-crystal neutron diffraction studies. Magnetization measurements under small applied magnetic field indicate two successive magnetic transitions, one from a ferromagnetic (FM) state to an antiferromagnetic (AFM) state (T$_\mathrm{C}=197$ K), and second from AFM to a paramagnetic state (T$_\mathrm{N}=211$ K). The FM transition is sharp with a strong presence of magnetoelastic coupling, but is not accompanied by any structural phase transition. The magnetic structure obtained from zero-field single crystal neutron diffraction reveals that the Cr1 and Cr2 moments are ferromagnetically aligned along the c-axis, while the Cr3 and intercalated Cr4 atoms induce an AFM component in the ab-plane leading to an umbrella-like spin structure which possesses a finite spin chirality. The presence of a finite spin chirality is responsible for the observation of the topological Hall effect (THE).