Nature of 2D XY antiferromagnetism in a van der Waals monolayer

TL;DR

This study uses magnetotransport measurements to explore the magnetic phase diagram of monolayer NiPS3, revealing unique in-plane hexagonal antiferromagnetic behavior and confirming theoretical models for 2D XY antiferromagnetism.

Contribution

It provides the first experimental phase diagram of monolayer NiPS3, demonstrating distinct magnetic transitions and validating 2D XY model predictions with hexagonal anisotropy.

Findings

Monolayer NiPS3 exhibits two magnetic transitions unlike multilayers.

The phase diagram aligns with six-state clock and 2D-XY models.

In-plane hexagonal anisotropy governs low-temperature magnetic behavior.

Abstract

Two-dimensional antiferromagnetism has long attracted significant interest in many areas of condensed matter physics, but only recently has experimental exploration become feasible due to the isolation of van der Waals antiferromagnetic monolayers. Probing the magnetic phase diagram of these monolayers remains however challenging because established experimental techniques often lack the required sensitivity. Here, we investigate antiferromagnetism in atomically thin van der Waals magnet NiPS3 using magnetotransport measurements in field-effect transistor devices. Temperature-dependent conductance and magnetoresistance data reveal a distinct magnetic behavior in monolayers as compared to thicker samples. While bilayer and multilayer NiPS3 exhibit a single magnetic phase transition into a zig-zag antiferromagnetic state driven by uniaxial anisotropy, monolayer NiPS3 undergoes two magnetic transitions, with a low-temperature phase governed by in-plane hexagonal magnetic anisotropy. The experimentally constructed phase diagram for monolayer NiPS3 matches theoretical predictions from the six-state clock and 2D-XY models incorporating hexagonal anisotropy.