Controlling noncollinear ferromagnetism in van der Waals metal-organic magnets

Van der Waals (vdW) magnets can be used to explore both fundamental 2D physics and offer a route to exploit magnetism in next generation information technology, but vdW magnets with complex, noncollinear spin textures are currently rare. We re- port here the syntheses, crystal structures, bulk magnetic properties and magnetic ground states of four vdW metal-organic magnets (MOMs): FeCl2(pym), FeCl2(btd), NiCl2(pym) and NiCl2(btd), pym = pyrimidine and btd = 2,1,3-benzothiadiazole. Using a combination of neutron diffraction and bulk magnetometry we show that these materials are noncollinear magnets and although only NiCl2(btd) has a ferromagnetic ground state, low-field hysteretic metamagnetic transitions also allow access to states with net magnetisation in zero-field and high coercivities for FeCl2(pym) and NiCl2(pym). By combining our bulk magnetic data with diffuse scattering analysis and broken-symmetry density-functional calculations we probe the magnetic superexchange interactions, which when combined with symmetry analysis allow us to suggest design principles for future noncollinear vdW MOMs.