Rare‐Earth Engineering of Fe 3 O 4 Sustainable Nanoparticles for Enhanced Magnetic Hyperthermia and Potential Electrochemical Applications

Abstract

Controlled rare‐earth substitution offers a powerful pathway to engineer multifunctional nanospinel systems with tunable physicochemical properties. In this study, phase‐pure 5 mol% Lu 3+ ‐doped Fe 3 O 4 nanoparticles were synthesized via a defect‐regulated hydrothermal strategy to modulate structural, magnetic, optical, and electrochemical characteristics. Powder X‐ray diffraction confirmed retention of the cubic inverse spinel structure without secondary phase formation, while XPS and EDS analyses verified successful substitutional incorporation of Lu 3+ and enhanced oxygen vacancy concentration. Structural perturbation induced measurable lattice strain without compromising crystallinity. Magnetic measurements revealed preserved ferrimagnetic ordering with tuned coercivity and optimized anisotropy. Optical analysis indicated band structure modulation with a narrowed bandgap (~1.6 eV), promoting enhanced visible–light interaction. Electrochemical impedance spectroscopy demonstrated reduced charge–transfer resistance, while LSV and Tafel analysis confirmed accelerated reaction kinetics and improved electrocatalytic activity. Additionally, the doped system exhibited efficient magnetic hyperthermia performance under alternating magnetic fields. The results establish Lu incorporation as an effective defect‐engineering strategy to simultaneously tailor exchange interactions, carrier transport, and surface reactivity in Fe 3 O 4 nanospinels, enabling advanced multifunctional applications in catalysis, energy conversion, and biomedicine.