Imaging thermally fluctuating N\`eel vectors in van der Waals antiferromagnet NiPS3

TL;DR

This study uses advanced microscopy to image and analyze thermally fluctuating Neel vectors in the van der Waals antiferromagnet NiPS3, revealing temperature-dependent magnetic domain behavior and anisotropy effects.

Contribution

It introduces a novel application of XMLD-PEEM to directly image Neel vectors in NiPS3 and uncovers thermally induced fluctuations independent of crystal symmetry.

Findings

Identification of multidomain structures in NiPS3

Observation of thermally fluctuating Neel vectors below TN

Link between small orbital moment anisotropy and weak magneto-crystalline anisotropy

Abstract

Studying antiferromagnetic domains is essential for fundamental physics and potential spintronics applications. Despite its importance, few systematic studies have been performed on van der Waals (vdW) antiferromagnets (AFMs) domains with high spatial resolutions, and direct probing of the N\`eel vectors remains challenging. In this work, we found a multidomain in vdW AFM NiPS3, a material extensively investigated for its exotic magnetic exciton. We employed photoemission electron microscopy combined with the X-ray magnetic linear dichroism (XMLD-PEEM) to image the NiPS3's magnetic structure. The nanometer-spatial resolution of XMLD-PEEM allows us to determine local N\`eel vector orientations and discover thermally fluctuating N\'eel vectors that are independent of the crystal symmetry even at 65 K, well below TN of 155 K. We demonstrate a Ni ions' small in-plane orbital moment anisotropy is responsible for the weak magneto-crystalline anisotropy. The observed multidomain's thermal fluctuations may explain the broadening of magnetic exciton peaks at higher temperatures.