Kitaev interaction and proximate higher-order skyrmion crystal in the triangular lattice van der Waals antiferromagnet NiI2

TL;DR

This study explores how Kitaev interactions in NiI2 can stabilize higher-order skyrmion crystals, revealing complex magnetic correlations and proposing NiI2 as a candidate for hosting such exotic topological spin textures.

Contribution

It demonstrates that Kitaev anisotropic exchange interactions can stabilize higher-order skyrmion crystals in a van der Waals antiferromagnet, supported by experiments and modeling.

Findings

Identification of incommensurate magnetic correlations in NiI2

Prediction of higher-order skyrmion crystal formation via simulations

NiI2 is proposed as a Kitaev bulk material near skyrmion phases

Abstract

Topological spin textures, such as magnetic skyrmions, are a spectacular manifestation of magnetic frustration and anisotropy. Most known skyrmion systems are restricted to a topological charge of one, require an external magnetic field for stabilization, and are only reported in a few materials. Here, we investigate the possibility that the Kitaev anisotropic-exchange interaction stabilizes a higher-order skyrmion crystal in the insulating van der Waals magnet NiI2. We unveil and explain the incommensurate static and dynamic magnetic correlations across three temperature-driven magnetic phases of this compound using neutron scattering measurements, simulations, and modeling. Our parameter optimisation yields a minimal Kitaev-Heisenberg Hamiltonian for NiI2 which reproduces the experimentally observed magnetic excitations. Monte Carlo simulations for this model predict the emergence of the higher-order skyrmion crystal but neutron diffraction and optical experiments in the candidate intermediate temperature regime are inconclusive. We discuss possible deviations from the Kitaev-Heisenberg model that explains our results and conclude that NiI2, in addition to multiferroic properties in the bulk and few-layer limits, is a Kitaev bulk material proximate to the finite temperature higher-order skyrmion crystal phase.