Microstructural and Magnetic Characterization of Iron Oxide Nanoparticles Fabricated by Pulsed Wire Evaporation

The iron oxide nanoparticles (IONPs) fabricated by pulsed wire evaporation were characterized by analytical electron microscopy and magnetic properties measurement system (MPMS). The IONPs produced at various charging voltages (2.6, 5.0 and 6.3 kV) exhibited the average size of 48 nm and the differences in shape, i.e., spherical (83%) and hexagonal (17%) structures. The hexagonal nanoparticles showed single-crystalline magnetite (Fe3O4) with major facets made of {111} planes. The chemical shifts in core–shell nanoparticles were observed by electron energy loss spectroscopy, indicating a dependency of the edge position related to the oxidation state of Fe. From the MPMS, the saturation magnetization and the coercivity of IONPs were measured to be 64 emu/g and 37 Oe at 300 K, respectively. The results provide useful information for the relationship between the nanostructure and magnetic behavior. TEM images of iron oxide nanoparticles (IONPs) fabricated by pulsed wire evaporation. Two distinct shapes of IONPs can be seen, i.e., hexagonal and core/shell structures. The hexagonal nanoparticles showed single-crystalline Fe3O4 magnetite with major facets made of {111} planes, while the core/shell nanoparticle consisted of Fe core and Fe3O4 shell. By magnetic property measurement system (MPMS), the saturation magnetization and the coercivity were measured to be 64 emu/g and 37 Oe at 300 K, respectively. This study provides the possibility for developing novel and various IONPs with unprecedented structures and/or magnetic properties.