$\textit{Ab initio}$ theory of magnetism in two-dimensional $1T$-TaS$_2$

TL;DR

This study uses first-principles density-functional calculations to explore the magnetic properties of monolayer 1T-TaS2, revealing ferromagnetic interactions and significant anisotropy, suggesting it could host an easy-plane XXZ quantum ferromagnet.

Contribution

It provides the first ab initio derivation of spin Hamiltonians for monolayer 1T-TaS2, including bilinear, biquadratic, and ring-exchange interactions, highlighting ferromagnetic tendencies and anisotropy.

Findings

Both quadratic and quartic interactions are ferromagnetic.

Relativistic calculations show substantial magnetocrystalline anisotropy.

Material may realize an easy-plane XXZ quantum ferromagnet.

Abstract

We investigate, using a first-principles density-functional methodology, the nature of magnetism in monolayer $1T$-phase of tantalum disulfide ($1T$-TaS$_2$ ). Magnetism in the insulating phase of TaS$_2$ is a longstanding puzzle and has led to a variety of theoretical proposals including notably the realization of a two-dimensional quantum-spin-liquid phase. By means of non-collinear spin calculations, we derive $\textit{ab initio}$ spin Hamiltonians including two-spin bilinear Heisenberg exchange, as well as biquadratic and four-spin ring-exchange couplings. We find that both quadratic and quartic interactions are consistently ferromagnetic, for all the functionals considered. Relativistic calculations predict substantial magnetocrystalline anisotropy. Altogether, our results suggest that this material may realize an easy-plane XXZ quantum ferromagnet with large anisotropy.