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 Cd²⁺ at both Co²⁺ and Cu²⁺ lattice sites in the Co_0.5Cu_0.5Fe₂O₄ spinel lattice. Nanoparticles with the nominal composition Co_0.5−xCu_0.5−xCd_2xFe₂O₄ (x = 0.00, 0.01, 0.02, 0.04, 0.06) were synthesized using an efficient co-precipitation method. The large ionic radius of Cd²⁺ promotes its occupation of tetrahedral sites, which disrupts the magnetocrystalline anisotropy associated with Co²⁺ and the Jahn–Teller distortions associated with Cu²⁺, 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_0.5Cu_0.5Fe₂O₄ as the primary phase and a minor hematite (Fe₂O₃) secondary phase. Increasing Cd²⁺ 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 Fe³⁺ migration towards tetrahedral sites. Additionally, XPS analysis confirmed the oxidation states of the constituent elements in the samples as Co²⁺, Cu²⁺, Fe³⁺, Cd²⁺and O²⁻. 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.