Sm/Gd and Sm/Gd/Nd co-doping for tailoring magnetic, dielectric, and optical properties in CoFe2O4 nanomaterials

Abstract

CoFe₂O₄ (CFO) nanoparticles were synthesized and co-doped with Sm/Gd (SGCF) and Sm/Gd/Nd (SGNCF) using an assisted hydrothermal method to systematically examine the impact of rare earth substitution on their structural, magnetic, dielectric, and optical properties. X-ray diffraction (XRD) confirmed the formation of a single-phase spinel structure across all samples, with increased crystallite size observed upon doping. X-ray photoelectron spectroscopy (XPS) reveals Fe³⁺ and Co²⁺ oxidation states and noticeable shifts in Fe 2p and Co 2p binding energies, indicating changes in the electronic structure and local chemical environment. O 1s spectra further evidence doping-induced modulation of surface oxygen species and vacancies. Cation distribution analysis shows balanced Co occupancy in CFO, with SGCF favoring tetrahedral stabilization and SGNCF displaying a shift toward octahedral coordination. Magnetically, SGCF exhibits enhanced saturation magnetization (M_s = 65.92 emu/g) and coercivity (H_c = 915.80 Oe), compared to undoped CFO, while SGNCF shows a reduced saturation magnetization with magnetic moment of 2.51 μ_B. Dielectric measurements reveal decreased permittivity and AC conductivity at low frequencies in the doped samples, attributed to reduced interfacial polarization and grain boundary effects. Optical studies indicate a slight band gap narrowing from 1.36 eV (CFO) to 1.34 eV (SGCF) and 1.31 eV (SGNCF), suggesting quantum confinement and structural distortion. These findings demonstrate that rare earth co-doping effectively tunes the multifunctional properties of CFO, enhancing its suitability for spintronic, dielectric, and optoelectronic applications.