Monolayer CrCl$_3$ as an ideal Test Bed for the Universality Classes of 2D Magnetism

TL;DR

This paper demonstrates that monolayer CrCl₃ can serve as a versatile platform for exploring various 2D magnetic phases, including Ising and BKT regimes, by tuning magnetic anisotropy through strain, supported by advanced simulations.

Contribution

It introduces the use of strain to tune magnetic anisotropy in monolayer CrCl₃, enabling the study of multiple 2D magnetic universality classes within a single material.

Findings

CrCl₃ exhibits tunable magnetic anisotropy under strain.

High BKT transition temperatures (~50 K) are achievable in CrCl₃.

Theoretical phase diagrams and magnon spectra support experimental feasibility.

Abstract

The monolayer halides CrX$_3$ (X=Cl, Br, I) attract significant attention for realizing 2D magnets with genuine long-range order (LRO), challenging the Mermin-Wagner theorem. Here, we show that monolayer CrCl$_3$ has the unique benefit of exhibiting tunable magnetic anisotropy upon applying a compressive strain. This opens the possibility to use CrCl$_3$ for producing and studying both ferromagnetic and antiferromagnetic 2D Ising-type LRO as well as the Berezinskii-Kosterlitz-Thouless (BKT) regime of 2D magnetism with quasi-LRO. Using state-of-the-art density functional theory, we explain how realistic compressive strain could be used to tune the monolayer's magnetic properties so that it could exhibit any of these phases. Building on large-scale quantum Monte Carlo simulations, we compute the phase diagram of strained CrCl$_3$, as well as the magnon spectrum with spin-wave theory. Our results highlight the eminent suitability of monolayer CrCl$_3$ to achieve very high BKT transition temperatures, around 50 K, due to their singular dependence on the weak easy-plane anisotropy of the material.