Ligand solid-solution tuning of magnetic and mechanical properties of the van der Waals metal-organic magnet NiCl2(btd)1–x(bod)x

Van der Waals (vdW) magnets offer unique opportunities for exploring magnetism in the 2D limit. Metal-organic magnets (MOM) are of particular interest because functionalising the organic ligands allows for control over their physical properties. Here, we demonstrate tuning of mechanical and magnetic functionality of a recently reported non-collinear vdW ferromagnet, NiCl2(btd) (btd = 2,1,3-benzothiadiazole), through creating solid-solutions with the oxygen-substituted analogue ligand 2,1,3-benzoxadiazole (bod). We synthesise solid-solutions, NiCl2(btd)1-x(bod)x, up to x=0.33 above which we find mixtures form, primarily composed of a new 1D coordination polymer NiCl2(bod)2. Magnetometry on this series shows that bod incorporation reduces the coercivity significantly (up to 60%), without significantly altering the ordering temperatures. Our high pressure synchrotron diffraction measurements up to 0.4 GPa demonstrate that the stiffest axis is the b axis, through the Ni-N-(O/S)-N-Ni bonds, and the softest is the interlayer direction. Doping with bod fine-tunes this compressibility, softening the layers, but stiffening the interlayer axis. This demonstrates how mixed-ligand strategy can be used to realise targeted magnetic and mechanical properties in vdW MOMs.