Complex magnetic structure and magnetocapacitance response in a non-oxide NiF₂ system

We report here on the complex magnetic structure and magnetocapacitance in NiF₂, a non-oxide multifunctional system. It undergoes an anti-ferromagnetic transition near 68.5 K, superimposed with canted Ni spin driven weak ferromagnetic ordering, followed by a metastable ferromagnetic phase at or below 10 K. Our density functional calculations account for the complex magnetic structure of NiF₂ deduced from the temperature and the field dependent measurements. Near room temperature, NiF₂ exhibits a relatively large dielectric response reaching >10³ with a low dielectric loss of <0.5 at frequencies >20 Hz. This is attributed to the intrinsic grain contribution in contrast to the grain boundary contribution in most of the known dielectric materials. The response time is 10 μs or more at 280 K. The activation energy for such temperature dependent relaxation is ~500 meV and is the main source for grain contribution. Further, a large negative magneto capacitance >90% is noticed in 1 T magnetic field. We propose that our findings provide a new non-oxide multifunctional NiF₂, useful for dielectric applications.