Higher-order skyrmion crystal in van der Waals Kitaev triangular antiferromagnet NiI2

Topological spin textures, such as magnetic skyrmions, hold great promise for spintronics applications. However, most known skyrmion systems are restricted to a topological charge of one and require an external magnetic field for stabilization. Here, we report the discovery of a skyrmion crystal with a topological number of two in an insulating van der Waals magnet NiI2. We unveil the static and dynamic magnetic correlations across three temperature-driven magnetic phases using neutron scattering measurements, simulations, and model optimisation. By employing a minimal Kitaev-Heisenberg Hamiltonian, we reproduce the experimentally observed excitations and confirm the emergence of the higher-order skyrmion crystal through Monte Carlo simulations. Remarkably, this exotic phase arises without the need for a magnetic field, presenting a novel platform for controlling complex spin textures in an accessible material. These findings establish NiI2 as a pivotal material, bridging fundamental quantum magnetism with advancements in skyrmionics and multiferroic technologies.
Comment: 12 pages, 4 figures