Extraordinary high dielectric constant, electrical and magnetic properties of ferrite nanoparticles at room temperature

Nanoparticles of spinel ferrites of basic composition Ni1-xCoxFe2O4 (0.0 <= x <= 0.05) were synthesized through modified co-precipitation method, and were characterized for structural, transport electrical and magnetic properties using XRD, HRTEM, FTIR, LCR meter and VSM techniques, respectively. XRD analysis showed that all the samples are single-phase cubic spinel in structure. The average crystallite sizes of the nanoparticles were found between 30 nm to 45 nm. Real and imaginary parts of the impedance (Z' and Z) suggested coexistence of two relaxation regimes: one was introduced by electrode polarization, while the other was attributed to the coeffect of grain and grain boundary effects. The dielectric constant of the samples was found very high, which showed non-Debye relaxation phenomena, while conductivity of the samples exhibited a two-segment behavior with frequency. The room temperature M- H curves suggested that the samples exhibit supermagnetism, and the saturation magnetization increases with increasing Co2+? ion substitution.