Engineering Graded Magnetic Anisotropy via Cation Interdiffusion in Core/Shell Nanoparticles.
basic_science · Level V
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- Record sourced from PubMed, PMID 40778632.
- Also identified by DOI 10.1021/acs.nanolett.5c03005.
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Abstract
Spinel ferrite nanoparticles (NPs) with controlled composition, size, and morphology have offered a wide range of functional properties, but engineering nonhomogeneous composition profiles remains elusive. Here, we use Fe<sub>3</sub>O<sub>4</sub>/CoFe<sub>2</sub>O<sub>4</sub> core/shell NPs as precursors to prepare compositionally graded NPs via controlled interfacial diffusion of metal cations. Electron-microscopy-based elemental mapping reveals that thermal annealing above 200 °C in an oxygen-rich atmosphere transforms the initially sharp core/shell interface into a compositionally graded spinel structure with a Co-rich outer layer. This cation redistribution results in pronounced changes in the magnetic properties, including a remarkable increase in coercivity and high-field susceptibility. Enhancement in the effective anisotropy is quantitatively described by modeling the time-dependent Co diffusion, enabling estimation of the cation diffusivity. These findings demonstrate a robust strategy for preparing anisotropy-graded spinel ferrite NPs, offering a broadly applicable approach to tailoring the properties of complex metal oxide nanostructures.