Suppression of magnetic ordering in XXZ-type antiferromagnetic monolayer NiPS3

Kangwon Kim,Cheol-Hwan Park,Hyeonsik Cheong,Kisoo Park,Tae Yun Kim,Gun Sang Jeon,Jae-Ung Lee,Soo Yeon Lim,Je-Geun Park,Sungmin Lee

doi:10.1038/s41467-018-08284-6

Abstract

How a certain ground state of complex physical systems emerges, especially in two-dimensional materials, is a fundamental question in condensed-matter physics. A particularly interesting case is systems belonging to the class of XY Hamiltonian where the magnetic order parameter of conventional nature is unstable in two-dimensional materials leading to a Berezinskii−Kosterlitz−Thouless transition. Here, we report how the XXZ-type antiferromagnetic order of a magnetic van der Waals material, NiPS3, behaves upon reducing the thickness and ultimately becomes unstable in the monolayer limit. Our experimental data are consistent with the findings based on renormalization-group theory that at low temperatures a two-dimensional XXZ system behaves like a two-dimensional XY one, which cannot have a long-range order at finite temperatures. This work provides the experimental examination of the XY magnetism in the atomically thin limit and opens opportunities of exploiting these fundamental theorems of magnetism using magnetic van der Waals materials.

Highlights

How a certain ground state of complex physical systems emerges, especially in twodimensional materials, is a fundamental question in condensed-matter physics
We investigated the magnetic signals in the form of two-magnon and QES as a function of the sample thickness down to the monolayer limit
All our experimental observations coherently point to the conclusion that the antiferromagnetic ordering persists down to two-layer samples and is drastically suppressed in the monolayer

Summary

Introduction

How a certain ground state of complex physical systems emerges, especially in twodimensional materials, is a fundamental question in condensed-matter physics. We report how the XXZ-type antiferromagnetic order of a magnetic van der Waals material, NiPS3, behaves upon reducing the thickness and becomes unstable in the monolayer limit. 1234567890():,; It is an enduring theme of physical science how a certain ground state emerges out of often complex underlying principles of nature Our understanding of this fundamental question captures all the essence of what we know about the system, be it cosmos or real materials. For the 2D Ising system (Jx = Jy = 0) the magnetic ground state is stable even in the 2D limit, whose experimental evidence has been recently presented using magnetic van der Waals materials: FePS3 9,10 with antiferromagnetic order and Cr2Ge2Te6 11 and CrI3 12 with ferromagnetic order

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Conclusion