Properties of the diamagnetic materials are: The diamagnetic materials have all the paired electrons, and none of the electrons is the valence, resulting in the absence of atomic dipoles in these materials. This happens because the overall magnetic moment of each atom in the compound cancels out.
[Ni(CO)4]→ diamagnetic, sp3 hybridization, number of unpaired electrons =0
If the substance contains unpaired electrons, it is a paramagnetic substance.
[NiCl4]2−, → paramagnetic, sp3 hybridization, number of unpaired electrons =2