Mössbauer studies of the structure of core/shell Fe$_{3}$O$_{4}/\gamma$-Fe$_{2}$O$_{3}$ nanoparticles

The phase composition, the structure of cores and shells, and the dependences of the shell thickness on the fabrication technique were determined by Mössbauer spectroscopy for core/shell Fe$_{3}$O$_{4}/\gamma$-Fe$_{2}$O$_{3}$ magnetic nanoparticles (MNPs) with (Fe$_{3}$O$_{4}$) cores of a fixed size (8 nm) and $\gamma$-Fe$_{2}$O$_{3}$ shells of a varying thickness (1, 3, or 5 nm). A layer on the MNP surface with a magnetic state differing from that in the bulk was found. It was also found that a spin-glass state probably exists between the core and the shell. The studied core/shell Fe$_{3}$O$_{4}/\gamma$-Fe$_{2}$O$_{3}$ MNPs have promising applications in various fields (e.g., biomedicine).