Structural, Dielectric, and Magnetic Characterization of Nanocrystalline Ni–Co Ferrites

Abstract

Spinel ferrites containing Nickel and Cobalt of composition with nominal formula Ni_(1−x)Co_(x)Fe₂O₄ (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) prepared by the coprecipitation method are reported. The single phase spinel formation of ferrites was confirmed by X-ray diffraction techniques. The lattice constants (a _th) were calculated based on the ionic radii of the constituents. The calculated lattice constants are smaller than the measured, because for calculations ideal ionic radii are used. The particle size calculated from the Scherrer formula varied within 15 to 33 nm. The dielectric constant and dielectric loss tangent measurement were carried out at room temperature as a function of frequency from 100 Hz to 3 MHz. Both the dielectric constant and dielectric loss tangent increased with increase in cobalt concentration. Ferrimagnetic transition temperature as a function of Co concentration was measured with the low field ac susceptibility apparatus. The ferrimagnetic transition (T _c ) was observed in the temperature range 573 to 720 K. The T _c decreased with the addition of Co concentration. The effect of Co concentration on the magnetic properties was investigated using a vibrating sample magnetometer (VSM). It was found that both magnetic saturation (M _s ) and coercivity (H _c ) increase with Co concentration.