Laves Phase Ferromagnetism and Core-Shell Nanoparticles
Mark Koten, Balasubramanian Balamurugan, Ralph Skomski, David Sellmyer, and Jeffrey Shield
Advanced processing tools such as inert gas condensation cluster deposition systems can be used to fabricate alloys on the nanoscale with novel crystal structures and complex morphologies such as core-shell and onion-like chemical partitioning. Different nanostructures can be designed through precise composition control and fine-tuning of gas-condensation parameters. Phases that are a challenge to form using bulk, top-down routes due to, for example, large differences in melting temperature between component elements can be synthesized. This is the case for the Fe-W Laves phase, which demands an exact composition with minimal error for its production. This phase has the formula Fe2W, and is predicted by theoretical calculations to be ferromagnetic. Recent synthesis of this phase via inert gas condensation demonstrated a saturation magnetization as high as 60 emu/g at low temperatures, consistent with the calculated value and is reasonably high for a rare-earth-free material. Also within this system, but at a more Fe-rich composition, core-shell nanoparticles were designed by taking advantage of the disparity between Fe and W surface energies and the immiscibility present within the system. Particles with this chemical segregation pattern often demonstrate interesting physical, chemical, or electrical properties as well as improved stability.
These programs are supported by the National Science Foundation, Division of Materials Research, Materials Research Science and Engineering Program, Grant 0820521.
Transmission electron microscopy (TEM) image of an Fe2W nanoparticle (a) and a map of the component atoms of the W-Fe nanoparticle with a W core (b).
Highlight InfoDate: Feb. 2015
Research Area: IRG1