Synthesis and Characterization of HfO₂@Fe₃O₄ Core–Shell Nanotubes: Insights into Potential Magnetic Functionalities

This study presents the synthesis and characterization of core–shell nanostructures comprising PVP@HfO2@Fe2O3 nanowires and HfO2@Fe3O4 nanotubes. PVP nanofibers were electrospun with an average diameter of approximately 379 nm, onto which HfO2 and Fe2O3 layers were sequentially deposited via atomic layer deposition, resulting in core–shell nanowires averaging 460 nm in diameter. Thermal reduction transformed Fe2O3 into Fe3O4, forming HfO2@Fe3O4 core–shell nanotubes. Characterization using scanning electron microscopy and high-resolution transmission electron microscopy confirmed the core–shell morphology, while energy-dispersive X-ray spectroscopy verified the elemental composition. Surface roughness analysis revealed fractal dimensions indicating increased roughness with thicker shells. X-ray photoelectron spectroscopy analysis identified Fe(II) and Fe(III) oxidation states and confirmed phase transformations from hematite to magnetite. Magnetic measurements demonstrated enhanced coercivity and saturation magnetization in HfO2@Fe3O4 structures compared to initial samples, showcasing the tunability of magnetic properties through core–shell engineering. This work highlights atomic layer deposition’s capability to fabricate precise core–shell nanostructures, offering tailored control over morphology and magnetic behavior for applications in advanced nanotechnologies.