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 & Aring; to 8.3629 & Aring; 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 (M-s), coercivity (H-c) and remanent magnetization (M-r) were obtained from VSM measurements. The decrease in M-s 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 H-c was observed from 1525 to 806 Oe for y = 0.00 to y = 0.08, respectively. All compositions of CoNbyFe2-yO4 show squareness ratio (M-r/M-s) values in the range of 0.4542-0.3214. The variation of magnetic parameters (M-s, H-c, M-r/M-s) 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.