Magnetic Properties of CoNbyFe2-yO4 (0.00 ≤ y ≤ 0.08) Nanomaterials Synthesized via Modified Sol–gel Autocombustion Route.

The present study reports the effect of niobium substitution on structural and magnetic properties of CoNbyFe2-yO4 (0.00 ≤ y ≤ 0.08) nanomaterials. XRD studies confirm the formation of pure cubic spinel phase with nanocrystalline nature of CoNbyFe2-yO4. The values of lattice parameters (a) decrease with Nb content (y) for CoNbyFe2-yO4, i.e. from a = 8.3656 Å to 8.3629 Å for y = 0.00 to y = 0.08, respectively. Crystallite sizes decrease with the increase of 'y' for CoNbyFe2-yO4, i.e. from 29 nm (y = 0.00) to 19 nm (y = 0.08). FTIR studies confirm the presence of two distinct IR bands in the range of 584 cm−1 – 590 cm−1 and 408 cm−1 – 410 cm−1 for stretching vibrations corresponding to the M–O bonds at tetrahedral and octahedral sites, respectively. FESEM micrographs illustrate the spherical morphology of CoNbyFe2-yO4. The values of saturation magnetization (Ms), coercivity (Hc) and remanent magnetization (Mr) were obtained from VSM measurements. The decrease in Ms was observed from 76.2 emu/g (y = 0.00) to 66.9 emu/g (y = 0.08) as a result of increase in 'y'. The significant deviation in the Hc was observed from 1525 to 806 Oe for y = 0.00 to y = 0.08, respectively. All compositions of CoNbyFe2-yO4 show squareness ratio (Mr/Ms) values in the range of 0.4542–0.3214. The variation of magnetic parameters (Ms, Hc, Mr/Ms) for CoNbyFe2-yO4 nanomaterials are best explained on the basis of varying Nb atom substitution leading to cation distributions and possible surface spin disorder due to size and surface effects. [ABSTRACT FROM AUTHOR]