Title: Novel Core-Shell Nanoparticles: Synthesis, Magnetism and Application 
 Speaker: Dr. You Qiang, associate professor of The University of Iowa , USA Time: 9:00 Am, Tuesday , July 5, 2011
 Place: Room 205, Bldg 14, SCUT North Campus
 Sponsor: School of Materials Science and Engineering

Abstract：
     Nanoparticles have gained extremely increased attention nowadays for energy, biomedical and environmental applications. Most magnetic nanoparticles (MNPs) are based on iron oxides with low specific magnetic moments of ~50 emu/g. In this presentation, I report room-temperature synthesis of novel iron-iron oxide core-shell MNPs using a newly developed nanocluster source.  Monodispersive iron MNPs with size of diameters from 1 to 100 nm are produced in a cluster source and then transmitted into the reaction chamber where a small partial pressure of O2 is present so that the iron MNPs are coated with uniform iron oxide shell. These shells act as passivation layers preventing further oxidation of the cores continued exposure to air.  The stable core-shell MNP was observed by XPS, XRD and HRTEM. The magnetic properties were measured by SQUID and VSM. The core-shell MNPs are superparamagnetic at room temperature for sizes less than 15 nm, and then become ferromagnetic when the cluster size increases. The specific magnetic moment of core-shell MNPs is size dependent, and increases rapidly from about 80 emu/g at the size of 3 nm to over 200 emu/g up to the size of 100 nm. The examples of using the high magnetic moment MNPs are: 1) magnetic separation nanotechnology in nuclear fuel recycling; 2) core-shell MNPs in cancer treatment; and 2) soft magnetic thin film for GHz communication.