Nickel ferrite is technologically important magnetic material extensively used in high frequency applications such as microwave
device due to its high resistivity and sufficiently low losses. It also finds application in the ferrofluids technology. Therefore,
ultrafine nickel ferrite was prepared by autocatalytic combustion of novel nickel ferrous fumarato-hydrazinate precursor.
The precursor was characterized by IR, AAS, TG and DTA, and a chemical formula of NiFe2(C4H2O4)3·6N2H4 was fixed. This precursor once ignited with a burning splinter at room temperature, glows and the glow spreads over the entire
bulk completing the autocatalytic combustion of the precursor to ultrafine ferrite. The single phase formation of ultrafine
nickel ferrite was confirmed by XRD, IR spectra and TEM. The average particle size of the ultrafine ferrite was found to be
∼20 nm by TEM. The observed lower value of saturation magnetization for nickel ferrite was due to the superparamagnetic nature
of the particles, which increased with the increasing sintering temperature. The ultrafine nickel ferrite was then sintered
at 1000°C for 5 h and was characterized by XRD, IR spectra, SEM and TEM. The variation of resistivity, Seebeck coefficient
and a.c. susceptibility as a function of temperature was measured for NiFe2O4 and the results are discussed.