Electrical and dielectric properties of nano crystalline Ni–Co spinel ferrites

Nanocrystalline samples of NixCo1–xFe2O4, where x = 1, 0.8, 0.6, 0.4, 0.2 and 0, were synthesized by chemical co-precipitation method. The spinel cubic phase formation of Ni–Co ferrite samples was confirmed by X-ray diffraction (XRD) data analysis. All the Bragg lines observed in XRD pattern belong to cubic spinel structure of ferrite. Scanning Electron Microscopy (SEM) technique was used to study the surface morphology of the Ni–Co ferrite samples. Nanocrystalline size of Ni–Co ferrite series was observed in SEM images. Pellets of Ni–Co ferrite were used to study the electrical and dielectric properties. The resistivity measurements were carried out on the samples in the temperature range 300–900 K. Ferrimagnetic to paramagnetic transition temperature (Tc) for all samples was noted from resistivity data. The activation energy below and above Tc was calculated. The dielectric constant (ɛ′) measurements with increasing temperature show two peaks in the temperature range of measurements for all samples under investigation. The peaks observed show frequency and compositional dependences as a function of temperature. Electrical and dielectric properties of nanocrystalline NixCo1–xFe2O4 samples show unusual behavior in temperature range of 500–750 K. To our knowledge, nobody has discussed such anomalies for nanocrystalline NixCo1–xFe2O4 at high temperature. Here, we discuss the mechanism responsible for electrical and dielectric behavior of nanocrystalline NixCo1–xFe2O4 samples.

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► Successful synthesis and characterization of nanocrystalline NixCo1–xFe2O4 ferrites.
► Ferrimagnetic to paramagnetic transition values of Ni–Co ferrite lie between 863 and 793 K.
► Unusual electric and dielectric behavior well above room temperature is discussed.