Structural and magnetic tailoring of Co-Cu ferrite nanoparticles via Cd2+ substitution: a multi-characterization approach

Abstract This study investigates the structural and magnetic tunability of Co–Cu ferrite nanoparticles via dual-site substitution of Cd 2+ at both Co 2+ and Cu 2+ lattice sites in the Co 0.5 Cu 0.5 Fe 2 O 4 spinel lattice. Nanoparticles with the nominal composition Co 0.5−x Cu 0.5−x Cd 2x Fe 2 O 4 (x = 0.00, 0.01, 0.02, 0.04, 0.06) were synthesized using an efficient co-precipitation method. The large ionic radius of Cd 2+ promotes its occupation of tetrahedral sites, which disrupts the magnetocrystalline anisotropy associated with Co 2+ and the Jahn–Teller distortions associated with Cu 2+ , leading to cation redistribution, modifications in superexchange interactions, and potentially the initiation of spin canting. Compared to single-site doping, this dual-site substitution introduces greater structural and magnetic complexity, offering a promising approach for multifunctional ferrite design. X-ray diffraction (XRD) confirmed a predominant face-centered cubic spinel phase with Co 0.5 Cu 0.5 Fe 2 O 4 as the primary phase and a minor hematite (Fe 2 O 3 ) secondary phase. Increasing Cd 2+ content induced a systematic lattice parameter expansion and crystallite size reduction (from 15.47 nm to 12.11 nm), indicating lattice distortion due to ionic substitution. TEM analysis showed quasi-spherical, slightly agglomerated nanoparticles with sizes decreasing from 15.47 nm to 12.11 nm as x increased from 0.00 to 0.06. HRTEM confirmed the material’s polycrystalline nature through observed (220) and (311) lattice fringes. FTIR spectra displayed two characteristic absorption bands 510–580 cm −1 and 400–450 cm −1 ) confirming spinel formation, while Raman spectroscopy revealed a blue shift in the $$\:{A}_{1g}$$ mode, associated with Fe 3+ migration towards tetrahedral sites. Additionally, XPS analysis confirmed the oxidation states of the constituent elements in the samples as Co 2+ , Cu 2+ , Fe 3+ , Cd 2+ and O 2− . Vibrating sample magnetometry (VSM) measurements showed ferromagnetic hysteresis loops with a non-linear variation of saturation magnetization ( $$\:{M}_{s}$$ ) and a significant reduction in coercivity ( $$\:{H}_{c}$$ ) from 851.98 G to 306.06 G, reflecting progressive magnetic softening with Cd²⁺ incorporation. Complementary, ESR analysis showed asymmetric resonance line shapes, a downshift in $$\:{H}_{r}$$ , and an enhancement in the Landé $$\:g$$ -factor, which was consistent with modifications in the local magnetic environment. These tunable structural and magnetic properties highlight the potential of Cd-substituted Co–Cu ferrites for applications in high-frequency electronics and EMI shielding.