Calcination effect on the magneto-optical properties of vanadium substituted NiFe2O4 nanoferrites

Vanadium substituted nickel ferrite nanoparticles (NPs), NiFe2-xVxO4 (0.0x0.3) were prepared by sol-gel approach. The influence of calcination on the magnetic and optical properties of NiFe2-xVxO4 (0.0x0.3) NPs were investigated deeply. The lattice parameters a' are almost constant with V-substitution for as-prepared and calcined samples. It was found that the calcination process both increased the crystallites size and removed the impurity phases in all products. The values of optical energy band gap, E-g, are in range of 1.38-1.69eV and 1.39-1.56eV for as-prepared and calcined samples, respectively. The specific magnetic parameters such as saturation magnetization M-s, remanence M-r, coercivity H-c, squareness ratio (SQR) and magnetic moment nB were determined from magnetization versus applied field measurements. The various M(H) curves exhibit ferromagnetic behavior at room temperature and 10K. A decrease in M-s, M-r and nB values was observed with Vanadium substitution. However, an increase in H-c value was observed. The obtained magnetic results are primarily resulted from the substitution of Fe ions with V ions that will weaken the A-B super-exchange interactions. Besides, the calcination step leads to an improvement in the various M-s, M-r and nB parameters. This enhancement is due to the enlargement of crystallites size (or grains size) and the strengthening of the A-B exchange interactions caused by the calcination effect. Nevertheless, the enlargement in the crystallites size is followed by a reduction in H-c values.