We present studies of the structural and magnetic properties of core-shell ironiron oxide nanoparticles. α-Fe nanoparticles were fabricated by sputtering and subsequently covered with a protective nanocrystalline oxide shell consisting of either maghaemite (γ -Fe 2 O 3 ) or partially oxidized magnetite (Fe 3 O 4 ). We observed that the nanoparticles were stable against further oxidation, and Mössbauer spectroscopy at high applied magnetic fields and low temperatures revealed a stable form of partly oxidized magnetite. The nanocrystalline structure of the oxide shell results in strong canting of the spin structure in the oxide shell, which thereby modifies the magnetic properties of the coreshell nanoparticles.

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