Xiaohan Sun

Iron-based magnetic nanomaterials have evolved into a versatile platform that integrates tuneable magnetic, electronic, and catalytic properties with chemical abundance and sustainability. While classical ferrites such as Fe ₃ O ₄ and γ -Fe ₂ O ₃ established the foundations for magnetic sensing, biomedical imaging, and environmental remediation, emerging demands for higher magnetic response, stronger field-induced heating, tailored spin polarization, and enhanced conductivity have driven a transition toward Fe-based alloys, carbides, nitrides, and heterostructured composites. These advanced phases offer expanded control over saturation magnetization, anisotropy, relaxation dynamics, and interfacial chemistry, unlocking capabilities that conventional oxides cannot achieve. This review unifies recent progress across magnetic fundamentals, synthesis, and cross-sector applications. We first outline the key magnetic phenomena that govern functional performance, including superparamagnetism which is primarily observed in nanoparticles with a particle size of less than 10 nm, magnetic anisotropy, phase-dependent magnetism, surface/interface spin disorder, and magnetothermal dissipation. We then highlight state-of-the-art synthetic strategies, ranging from metal–organic framework-derived architectures and non-equilibrium phase engineering to hybrid core–shell and heterostructured systems, that enable precise control over composition, crystallinity, and metastable magnetic phases. Finally, we map these materials onto major technological domains, emphasizing how their magnetic and catalytic attributes drive advances in electrocatalysis (oxygen evolution reaction; hydrogen evolution reaction; and oxygen reduction reaction), energy storage and electronics (Li-ion batteries, Zn–air, spintronics), biomedicine (magnetic resonance imaging, magnetic hyperthermia, targeted drug delivery and magnetic particle imaging), and environmental remediation (wastewater treatment, dye degradation, and heavy metal removal). By integrating magnetic physics with chemical design and application engineering, this review provides an integrated framework for understanding and optimizing Fe-based nanomaterials. We conclude by identifying key challenges, including stabilization of non-equilibrium phases, achieving corrosion-resistant high-saturation magnetization systems, mechanistic spin-reactivity coupling, and the need for data-driven discovery, and outline a roadmap for accelerating the translation of iron-based magnetic materials into next-generation sustainable technologies.