Structural characterization and tuning of magnetic properties of CoVδFe2−δO4 (0.0 ≤ δ ≤ 0.9) nanomaterials synthesized via a modified sol–gel autocombustion method

Abstract

We report magnetic properties of CoV_δFe_2−δO₄ nanomaterials synthesized via a modified sol–gel autocombustion method. Lattice parameters obtained from X-ray diffraction (XRD) studies varied from 8.348 to 8.285 Å for δ = 0.0–0.9. Crystallite sizes estimated using Williamson–Hall (W–H) plots were found to be in the range of 52–30 nm (δ = 0.0–0.9). Lattice strain varied from 1.34 × 10⁻³ to 2.00 × 10⁻³ for δ = 0.0–0.9. Fourier transform infrared (FTIR) studies revealed peak positions in the ranges of 589.2–602.9 and 409.3–419.5 cm⁻¹ for tetrahedral (T_d) and octahedral (O_h) coordination, respectively. Raman spectra showed peaks corresponding to T_2g(3), E_g(2), E_g(1), T_2g(2), T_2g(1), A_1g(2) and A_1g(1) modes. Particle sizes obtained from field emission scanning electron microscopy (FESEM) analysis varied from 56 to 34 nm for δ = 0.0–0.9. Values of saturation magnetization (M_s) showed significant variation from 82.5 to 47.3 emu g⁻¹ for δ = 0.0–0.9. Coercivity (H_c) values (at 300 K) decreased from 1180 (δ = 0.0) to 886 Oe (δ = 0.9). The estimated values of M_s and H_c (at 5 K) varied from 74.8 to 48.9 emu g⁻¹ (δ = 0.0 to 0.9) and from 7772 to 7078 Oe (δ = 0.0 to 0.9), respectively. XPS study confirmed the redistribution of Co²⁺ and Fe³⁺ ions in Oh and Td sites, agreeing well with the magnetic behaviour. The observed decrease in H_c values were also related to a decrease in anisotropy constant (K₁), i.e. from 1.44 × 10⁴ to 1.19 × 10⁴ J m⁻³ for δ = 0.0–0.9.