Magnetism of size and shape controlled core-shell nanoparticles*
Abstract
We report here a new approach to synthesize monodispersive, high magnetic moment core-shell structured nanoparticles produced by our newly developed nanocluster deposition system. The Fe or Co nanoparticles are produced from a Sputtering-Gas-Aggregation cluster source and then go to the deposition chamber, where the nanoparticles are coated with oxides by introducing a small mount (2-4 sccm) of oxygen gas. Mean particle size range between 2 to 100 nm is easily controlled by adjusting the particle growth parameters, such as growth length and the ratio of Ar to He gas fluxes. The size distribution of nanoparticles is below 10% measured by TEM. HRTEM images show the shells covered very uniformly on the Fe or Co cores. The shape of nanoparticles can be easily changed by increasing the particle size. The particles are spherical if the size < 12 nm, and become non-spherical changing from tetrahedron, hexahedron to octahedron when the size increases from 15 nm to 100 nm. The magnetic properties measured by MPMS XL-7 system tell us that the core-shell nanoparticles are superparamagnetic without coercivity at room temperature for particle size smaller then 15 nm. The coercivity increases from 25 Oe for 15 nm to about 1 kOe of 100 nm size particles. Magnetic phase transition of size and shape dependece has been discussed. The size dependent interparticle interactions have been investigated by measuring the ZFC and FC curves and MFM. *Research supported by Idaho NSF-EPSCoR, ONR, DOE/PNNL and URO-UI.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARJ36014A