Electrical and magnetic properties of chromium-substituted cobalt ferrite nanomaterials

A series of chromium-doped cobalt ferrite, CoCrxFe2−xO4 (0.0 ≤ x ≥ 1.0), samples were prepared by a micro-emulsion method using polyethylene glycol (PEG) as surfactant at pH 9.50. The crystallite sizes (D) are found in the range 40–75 nm. The values of lattice parameter (a) decrease but those of the X-ray density (dx) and bulk density (db) increase by increasing chromium contents, x, of the sample. The observed decrease in dc-electrical resistivity with increase in temperature indicates semiconducting nature of the samples. The observed decrease in resistivity is due to decrease in the electron hopping by chromium substitution. Activation energy of hopping increases from 0.34 ± 0.02 eV (x = 0.0) to 0.52 ± 0.02 eV (x = 1.0) because the Cr3+ ions entering the octahedral sites would reduce the electron exchange between Fe2+ and Fe3+. Comparatively higher blocking temperature (TB) for the sample with chromium content x = 0.2 was obtained which is noted to decrease with further increase in chromium content (x > 0.2) in the samples. The magnetic saturation (MS) is found to have maximum value for the composition CoCr0.2Fe1.8O4 while coercivity (HC) decreases with increase in Cr3+ concentration in the samples indicating the loss of magneto crystalline anisotropy.