Structure and Magnetic Properties of Nanopowders of Iron Oxides and Hybrid Nanopowders of the Core–Shell Type Based on Them

Abstract

The results are presented from complex phase structural and magnetic studies for uncoated and hybrid nanopowders based on iron oxide of the core–shell type (Fe_3−xO₄@SiO₂). Their phase and structural characteristics are determined along with their and morphologies. It is shown that the nanopowders are nonstoichiometric magnetite Fe³⁺[Fe_1-3
x²⁺Fe_1+2
x³⁺V_x]О₄ in which there are volume and surface regions that differ by the electronic state of their iron ions. The results from magnetic measurements reveal a relationship between the dispersity and magnetic properties of nanopowders. The change in the thickness of a defect surface layer and its specific magnetization is analyzed quantitatively as a function of the mean size of magnetite nanoparticles and the presence of a coating. The resulting dependences are constructed and analyzed.