Electrical properties of NiFe2O4 epitaxial ultra-thin films

Epitaxial thin films of NiFe2O4 are fabricated by pulsed laser deposition on SrTiO3 substrate. Symmetrical capacitor-like structures are formed using SrRuO3 as bottom and top electrodes. Electrical characterizations, including current–voltage, capacitance–voltage and capacitance–frequency measurement, reveal a hysteresis-like behaviour for current and capacitance as function of voltage. This could be assigned to a resistive and/or capacitive switching. A “degradation” process takes place after repeated voltage cycling or after heating the sample to 400 K, leading to the stabilization of different resistive states. These features can be related to the changes observed in the capacitance–frequency characteristics, suggesting the presence of a relaxation mechanism at low frequencies, and can be associated with the presence of a deep donor-type level in the band-gap of the NiFe2O4 layer.