Structural and Magnetic Properties of Pb-substituted CuFe2O4 Nanoparticles

Lead-substituted copper ferrites (Cu1-xPbxFe2O4, x = 0.0–0.30) were synthesized via a sol–gel auto-combustion route to explore the structural and magnetic effects of Pb²⁺ incorporation. X-ray diffraction confirmed a tetragonal spinel phase (I41/amd) for low Pb content, which gradually evolved into a pseudo-cubic structure at higher substitution levels. The lattice parameters increased systematically with Pb doping, indicating lattice expansion and suppression of Jahn–Teller distortion. FTIR spectra revealed a red shift of both tetrahedral and octahedral metal–oxygen stretching modes, consistent with elongation of M–O bonds and partial Pb2+ occupancy of both sites. Magnetic measurements showed soft-ferromagnetic behavior with a notable increase in saturation magnetization (Ms) up to x = 0.25, followed by a decrease at higher Pb levels due to secondary phase formation and lattice strain. The reduction in coercivity (Hc) with Pb content reflects a weakening of magnetocrystalline anisotropy and lattice relaxation. These results highlight the structural flexibility and magnetic tunability of Pb-substituted CuFe2O4, emphasizing the role of large, nonmagnetic cations in controlling spinel ferrite functionality.