Core-shell Au/Fe₃O₄ nanocomposite synthesized by thermal decomposition method: Structural, optical, and magnetic properties

Core-shell structure Au@Fe₃O₄ nanoparticles was synthesized via a thermal decomposition method, evidencing through interplanar atomic distances of ~ 0.23 nm and ~ 0.48 nm finding in the center and the shell of the particles, matching to the (1 1 1) Au and (1 1 1) magnetite planes, respectively. The nanocomposite has an average diameter of the core of ~ 10.5 nm and a thickness of the shell of ~1.85 nm, accessed by TEM. X-ray diffraction carried out on the sample shows the crystal structure of fcc Au and fcc Fe₃O₄ without a spurious crystalline phase. Besides, Rietveld refinement displays an outer diameter of ~ 8.1 and ~ 12.3 for the core and shell, respectively, the latter using the Scherrer constant of 0.9 and 1.43, respectively. The UV–vis characterization result shows a surface plasmon resonance spectra of Au@Fe₃O₄ nanoparticles at ~ 540 nm, which advise a successful core–shell coupling of Au and the Fe₃O₄. Finally, the magnetic response displays a system with a superparamagnetic state at room temperature and with a distribution of blocking temperatures associated with the enhanced surface contribution related to the hollow magnetite structure's inner and outer surface. From the mean T_B, the effective magnetic anisotropy K_eff1.7×10⁴ J/m³ was obtained, which is in agreement with the expected for the magnetite phase.