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.