Abstract
We report a facile one-pot chemical synthesis of colloidal FePt@Fe3O4 core–shell nanoparticles (NPs) with an average diameter of 8.7 ± 0.4 nm and determine their compositional morphology, microstructure, two-dimensional strain, and magnetic hysteresis. Using various state-of-the-art analytical transmission electron microscopy (TEM) characterization techniques—including high resolution TEM imaging, TEM tomography, scanning TEM-high angle annular dark field imaging, and scanning TEM-energy dispersive x-ray spectroscopy elemental mapping—we gain a comprehensive understanding of the chemical and physical properties of FePt@Fe3O4 NPs. Additional analysis using x-ray photoelectron spectroscopy, x-ray diffraction, and superconducting quantum interference device magnetometry distinguishes the oxide phase and determines the magnetic properties. The geometric phase analysis method is effective in revealing interfacial strain at the core–shell interface. This is of fundamental interest for strain engineering of nanoparticles for desirable applications.
Highlights
FePt nanoparticles (NPs) represent a diverse class of alloy with a specific attraction over pure metal counterparts due to their high magneto-crystalline anisotropy and chemical stability
The FePt@Fe3O4 NPs were quantified by the following methods: (i) conventional transmission electron microscopy (TEM) for size distribution analysis, (ii) inductively coupled plasma optical emission spectroscopy (ICP-OES) for chemical composition determination, (iii) conventional powder x-ray diffraction (XRD) for phase determination and (iv) x-ray photoelectron spectroscopy (XPS) for chemical surface compositional analysis to distinguish the complex composition of the Fe oxide shell
The same result is expected for geometric phase analysis (GPA) of a FePt@Fe3O4 nanoparticle: in the coordinate system of the FePt, the Fe3O4 will be expected to show a linear variation of phase in the direction of the Bragg peak selected for the dark-field imaging
Summary
923-1292, Japan 4 Department of Physics & Astronomy, University College, London, WC1E 6BT, UK 5 School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan 6 Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot, Oxon, OX11 0FA, UK 7 Author to whom any correspondence should be addressed.
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