Engineering complex Fe₃O₄ Nano-octopods: A two-step approach for magnetic nanomaterials with high anisotropy

Anisotropic iron oxide nano-octopods (NOs) present unique morphological and magnetic characteristics that unlock diverse applications in environmental remediation, catalysis, and biomedicine. Here, we report a novel two-step synthetic approach to produce highly anisotropic, monodisperse Fe₃O₄ NOs with well-defined branched architecture and an average edge length of approximately 166 nm. First, thermal decomposition yields branched core@shell FeO@Fe₃O₄ structures, which subsequently undergo controlled solvent-mediated thermal oxidation of the FeO core, to obtain Fe3O4 NOs with high magnetic anisotropy and overall magnetic response. Comprehensive characterization by Transmission Electron Microscopy (TEM), Small-Angle X-ray Scattering (SAXS), X-Ray Diffraction (XRD), and Superconducting Quantum Interference Device (SQUID) magnetometer reveals the evolution of the structural and magnetic properties throughout the oxidation process. The resulting Fe₃O₄ NOs, to the best of our knowledge, exhibit the highest coercivity values at room temperature among magnetite particles of different sizes and shapes reported in the literature. This outstanding result is attributed to the combined effect of the NO size and the high density of crystallographic defects. Thus, their morphological complexity and superior magnetic functionality make them promising multifunctional nanomaterials for environmental cleanup, thermally activated and catalytic processes.