Magnetic and interface properties of the core-shell Fe₃O₄/Au nanocomposites

Highlights: • Core-shell Fe₃O₄@Au nanostructures obtained with an advanced two step synthesis. • Mössbauer data revealed interaction between iron and gold atoms at the interface. • Gold covering of Fe₃O₄ stabilizes the magnetic properties of magnetite. - Abstract: Core-shell Fe₃O₄/Au nanostructures were obtained with an advanced method of two step synthesis and several complementary methodics were applied for investigation structural and magnetic properties of the samples. Along with X-ray diffraction and transmission electron microscopy, electron diffraction, optical, Raman and Mössbauer spectroscopy were used for nanoparticle characterization. It was established that the physical and structural properties Fe₃O₄/Au nanocomposites are specific of intrinsic properties of gold and magnetite. Mössbauer and Raman spectroscopy data indicated that magnetite was in a nonstoichiometric state with an excess of trivalent iron both in the initial Fe₃O₄ nanoparticles and in the Fe₃O₄/Au nanocomposites. As follows from the Mössbauer data, magnetic properties of iron ions in the internal area (in core) and in the surface layer of magnetite nanoparticles are different due to the rupture of exchange bonds at the particles surface. This leads to decrease in an effective magnetic moment at the surface. Gold atoms at the interface of the composites interact with dangling bonds of magnetite and stabilize the magnetic properties of the surface layers of magnetite.