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arXiv · 2502.14167

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

Chaebin Kim·Olivia Vilella·Youjin Lee·Pyeongjae Park·Yeochan An·Woonghee Cho·Matthew B. Stone·Alexander I. Kolesnikov·Yiquing Hao·Shinichiro Asai·Shinichi Itoh·Takatsugu Masuda·Sakib Matin·Sujin Kim·Sung-Jin Kim·Martin Mourigal·Je-Geun Park
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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.

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Chaebin Kim, Olivia Vilella, Youjin Lee, Pyeongjae Park, Yeochan An, Woonghee Cho, Matthew B. Stone, Alexander I. Kolesnikov, Yiquing Hao, Shinichiro Asai, Shinichi Itoh, Takatsugu Masuda, Sakib Matin, Sujin Kim, Sung-Jin Kim, Martin Mourigal, Je-Geun Park. 2025-02-20. Kitaev interaction and proximate higher-order skyrmion crystal in the triangular lattice van der Waals antiferromagnet NiI2. https://arxiv.org/abs/2502.14167

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