Exotic magnetism in 2D Ni-based halides

Driven by the increasing enthusiasm towards long-range magnetic order in two-dimensional materials (2D) (such as CrI3 and CrGeTe3), we carry out simulations based on density functional theory (DFT) for halides, focusing in particular on Ni-(VII)2 (VII = Cl, Br, I) monolayers. In addition to standard analysis of structural and electronic properties, we put special emphasis on the magnetic properties, in terms of magnetic moments, Heisenberg exchange coupling (including anisotropic and off-diagonal terms in the exchange tensor) and magnetic anisotropy energy. Moreover, starting from DFT results and mapping total energies on model spin Hamiltonians, we perform Monte-Carlo simulations to investigate the ground-state magnetic ordering and trends at finite temperatures and upon magnetic fields. Our predictions suggest a particularly rich phase diagram for Ni iodide and bromide monolayers, with exotic non-collinear spin configurations and complex topological transitions.