Understanding High Anisotropic Magnetism by Ultrathin Shell Layer Formation for Magnetically Hard–Soft Core–Shell Nanostructures

Abstract

Magnetic core–shell nanostructures offer a viable solution for tunable magnetism via nanoscale exchange interactions in a single-component unit. A typical synthetic approach for monodisperse bimagnetic ferrite core–shell nanostructures employs the seed-mediated growth method using the heating-up process. Understanding magnetic core–shell interface formation and their interactions is crucial; however, the magnetical persistence of the pristine core component during the heating-up process is unclear. Here, we elucidate the enhancement mechanism of magnetic anisotropy when the hard–soft core–shell nanostructures are formed with the ultrathin shell layer. The heating-up effect on the core component exhibits the coordination change of ligand chemisorption with surface metal ions, which leads to a substantial increase in surface anisotropy due to enhanced spin–orbit couplings. We further demonstrate that the selection of metal precursors and surfactants for additional shell layer formation is important. The kin...