Effect of chromium ion substitution on the electromagnetic properties of nickel ferrite

Polycrystalline ferrites with general formula NiFe2−xCrxO4 (0 ≤ x ≤ 1) were prepared through oxalate impregnation method. The samples were characterized using DTA–TG, XRD, FT-IR, AC conductivity, VSM and magnetic susceptibility measurements. All compositions show cubic Spinel structure. Lattice constant slightly decreases with increasing chromium content. Average crystallite size lays in the range 147–170 nm. FT-IR studies show two absorption bands (ν1 and ν2) near about 600 cm−1 and 400 cm−1 for tetrahedral and octahedral sites, respectively. No shift was observed in band position at frequency ν1 by increasing Cr content, meanwhile the frequency ν2 is shifted to higher frequencies with increasing Cr content. AC conductivity measurements as a function of temperature showed that the samples behave like semiconductors. The decrease in the conductivity with increasing Cr content is due to limiting the degree of Fe2+–Fe3+ conduction in the octahedral site by introducing Cr which has preference to substitute octahedral Fe3+ ions. The saturation magnetization decreases linearly with increasing Cr content, whereas coercivity increases. Nèel's magnetic moments calculated from expected cation distributions in comparison with that from hysteresis loop gives satisfactory results up to x = 0.8. Magnetic susceptibility measurements revealed that all the samples have ferrimagnetic properties which changed to paramagnetic materials by increasing temperature. The Curie temperature and molar magnetic susceptibility were observed to decrease with increasing Cr content.