Effect of particle size on transport properties of NiFe2O4 nanoparticles

The magnetic field dependent ac electrical properties of NiFe2O4 nanoparticles with crystallite size of ∼14, 21 and 31 nm have been studied at room temperature. To prepare NiFe2O4 nanoparticles, pyrophoric chemical process has been employed. X-ray diffraction pattern shows the formation of NiFe2O4 nanoparticles. The dielectric constant has been decreased whereas real and imaginary parts of impedance are found to increase with increase in applied dc magnetic field as well as particle size. The interfacial polarization at the grain boundaries is higher for smaller particle size;hence, the dielectric constant has been found to maximum at 14 nm sample. There are two different semicircle has been observed at different frequency region in Nyquist plots for all the samples. The grain resistance for all the samples are found to increase with increase in magnetic field may be due to the magnetostrictive properties of NiFe2O4 nanoparticles. The semicircles due to grains are increased with increase in particle sizes. The ac conductivity study reveals the charge carrier conduction process is associated with hopping mechanism in the nanoparticles.