Tailoring Structural and Magnetic Properties of Co–Zn Ferrite Nanoparticles via Erbium Substitution

Co _0.5 Zn _0.5 Er _x Fe _2−x O ₄ (x = 0.00–0.10) nanoferrites were synthesized by sol-gel auto-combustion process to explore the impact of Er³⁺ substitution on their structural, microstructural, vibrational, thermal, and magnetic characteristics. X-ray diffraction with Rietveld refinement confirmed the formation of a single-phase cubic spinel structure with the lattice parameter increasing from 8.3954 Å (x = 0.00) to 8.4118 Å (x = 0.08) upon Er incorporation. Williamson–Hall analysis revealed a reduction in crystallite size from 38.3 nm to 16.6 nm across the substitution series, consistent with lattice strain induced by Er substitution. Thermal analysis indicated a total weight loss of ~ 11.24% with a major exothermic crystallization event at 318°C, confirming the formation of thermally stable ferrites. FTIR spectra displayed characteristic M–O vibrations near 530 cm⁻¹ and 420 cm⁻¹, with calculated force constants decreasing from 15.21 N/m to 15.11 N/m (tetrahedral) and 5.42 N/m to 5.37 N/m (octahedral), indicating lattice softening with Er substitution. TEM and HRTEM analyses confirmed quasi-spherical nanoparticles with particle sizes reducing from 35 nm to 22 nm, with measured interplanar spacings increasing from 1.92 Å (P1) to 2.97 Å (P3). Magnetic studies using VSM revealed soft magnetic behavior with low coercivity (~ 1.5–2.0 Oe) and a decrease in saturation magnetization from 28.4 emu/g to 21.2 emu/g with increasing Er content. These findings demonstrate that Er³⁺ substitution effectively tailors the structural and magnetic properties of Co–Zn ferrite nanoferrites, making them suitable for high-frequency and EMI shielding applications.