Cobalt substituted nickel ferrites via Pechini's sol-gel citrate route: X-band electromagnetic characterization

Cobalt substituted nickel spinel ferrites were synthesized in the form of Ni1-x,CoxFe2O4(x = 0-1, Delta x = 0.15) via Pechini's sol-gel citrate method with final sintering at 1000 degrees C for 6 h. Structural purity of the prepared ferrites is examined by using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Thermo-gravimetric and differential thermal analysis (TG-DTA) show that the formation of spinel phase is completed upto 700 degrees C. Lattice constant, cationic distribution and cationic site parameters are estimated from XRD data. For the first time, lattice parameter (a) is determined using four different methods and quite similar values are obtained in those. Characteristic peaks of nickel ferrites are observed in the Raman spectrum of each ferrite composition. Grain size (80-95 nm) is observed to be higher than crystallite size (26.2-31.8 nm) due to agglomeration of grains. Mossbauer spectra recorded at 300 K temperature show the presence of iron in only +3 valency. Variations of isomer shift, hyperfine field, quadrupole splitting and line width are analyzed with the amount of doped cobalt. This paper also presents the electromagnetic and shielding properties of these Ni-Co ferrites in X-band (8.2-12.4 GHz) frequency range using vector network analyzer (VNA). The analysis of shielding effectiveness shows that increasing the amount of cobalt in nickel ferrites results in increase in shielding efficiency of the ferrites which proves the utility of this specific doping.