The composition and magnetic structure of Fe$_{3}$O$_{4}$/$\gamma$-Fe$_{2}$O$_{3}$ core–shell nanocomposites at 300 and 80 K: Mössbauer study (Part I)

The magnetic structure and the composition of Fe$_{3}$O$_{4}$/$\gamma$-Fe$_{2}$O$_{3}$ nanoparticles are studied at 300 and 80 K with Mössbauer spectroscopy. We found that the Fe$_{3}$O$_{4}$/$\gamma$-Fe$_{2}$O$_{3}$ particles are a core–shell nanocomposite (NC), in which magnetite Fe$_3$O$_4$ is covered with a maghemite shell ($\gamma$-Fe$_{2}$O$_{3}$). We showed that the thickness of the maghemite shell ($\gamma$-Fe$_{2}$O$_{3}$) depends on synthesis technology. We found that a layer, whose magnetic structure differs from that of the inner part of the shell ($\gamma$-Fe$_{2}$O$_{3}$), is formed on the surface of the maghemite shell ($\gamma$-Fe$_{2}$O$_{3}$) in the Fe$_{3}$O$_{4}$/$\gamma$-Fe$_{2}$O$_{3}$ NC. An intermediate layer is formed in the spin-glass state between the core and the shell. The data on structure of core–shell nanocomposites open up prospects to explain the properties of such particles, which are of great interest to use in various fields, including biomedicine.