Magnetic exchange Hamiltonian of the spin-helix material NiI₂from paramagnetic scattering and Possible Skyrmion Phase

Magnetic Van-der-Walls materials have experienced a surge of interest driven by the plethora of distinct magnetic phases that they can host and the possibilities to produce new artificial materials and interfaces with an eye towards applications. To maximize impact in this burgeoning area, it is necessary to understand the magnetic and electronic Hamiltonians of these systems in detail, including magnetic exchanges, charge gaps, transfer integrals, magnetic transition temperatures and associated structures, anisotropies, etc. The family of transition metal dihalides and trihalides MX2 and MX3 provides several Van-der-Walls materials with a large diversity of magnetic phases. A recent theoretical study points at nickel dihalide NiI2 as a likely realization of the Higher-Spin Kitaev triangular model due to ligand effects and strong Hund’s coupling at the nickel site, as well as a magnetic skyrmion phase from exchange and/or single ion anisotropy. In this talk we report inelastic neutron scattering measurements on NiI2 that uncover previously reported incommensurate magnetic Bragg peaks as well as diffuse and inelastic neutron scattering responses that are essential to understand the competing ferromagnetic and antiferromagnetic interactions in this compound.