연구홍보포털

논문 초록 (Abstract)

Low feld magnetocapacitance (MC) efect is studied in an inhomogeneous medium with ferromagnetic conducting and antiferromagnetic semiconducting content. The inhomogeneous medium was synthesized by solution combustion method with variation of fuel to oxidant ratio. Antiferromagnetic pure NiO and ferromagnetic Ni dispersed in NiO matrix were formed using single step combustion due to induced self-reduction in precursors. A crystallographic compression was observed in the NiO lattice with reduced Ni. The magnetocapacitance efect was evaluated in these, using relaxation analysis of the magneto-dielectric dispersion with modifed Havriliak–Negami model. It was observed that the permittivity relaxation time was of the order of~ 16 to 35 ms at 1.2 kOe in capacitors with magnetic content whereas in pure NiO it was of the order of~65 μs. The analysis using macrospin approximation indicated dipole–dipole-like interaction or interface dominant MC of the order of+7.5% at 1.2 kOe in pure NiO, whereas in Ni–NiO it was exchange mediated at higher frequencies and intermediate magnetic felds with – 4.15% MC at 1.2 kOe. The dominance of spin accumulation over spin dependent scattering was established by comparing MC with magnetoresistance (MR). The MR content was found to be of the order of~ – 4% for capacitors with ferromagnetic component in the low feld region indicating signifcant spin dependent scattering along with spin accumulation. Whereas in pure NiO the MR was of the order of – 0.6% indicating very low spin dependent scattering. AC reactance of the device was also evaluated to establish the interactions and strength of spin dependent scattering in these capacitors. The power analysis of magnetocapacitance indicated that Ni–NiO capacitors had coherent spin scattering with increased exchange mediated nonlinear, non-local interaction (long range) and magnetoelectric coupling whereas in NiO it was local interaction mediated by pronounced dipolar coupling.