LAUSR

Abstract A systematic investigation of magnetic nanoparticles and the formation of a core-shell structure, consisting of multiple maghemite ( γ - Fe 2 O 3 ) nanoparticles as the core and silica as the shell, has been performed using various techniques. High-resolution transmission electron microscopy clearly shows isolated maghemite nanoparticles with an average diameter of 13 nm and the formation of a core-shell structure. Low temperature Mossbauer spectroscopy reveals the presence of pure maghemite nanoparticles with all vacancies at the B-sites. Isothermal magnetization and zero-field-cooled and field-cooled measurements are used for investigating the magnetic properties of the nanoparticles. The magnetization results are in good accordance with the contents of the magnetic core and the non-magnetic shell. The multiple-core γ - Fe 2 O 3 nanoparticles show similar behavior to isolated particles of the same size.