Neutron Powder Diffraction of Carbon-Coated FeCo Alloy Nanoparticles

Published

June 1, 1999

Author(s)

J H. Scott, K Chowdary, Z Turgut, S. A. Majetich, M E. McHenry

Abstract

Neutron powder diffraction is used to study the order-disorder transformation in carbon-coated Fe_xCo_1-x nanoparticles produced using a radio frequency (RF) plasma torch. The nanoparticles, nominally Fe₅₀Co₅₀, are produced from alloy powder and acetylene precursors by gas-phase nucleation from the plasma. The resulting nanoparticles undergo an order-disorder transformation near 730 degrees C, passing from an ordered B2 (CsCl) structure to a disordered A1 (bcc) structure upon heating, similar to the transformation seen in bulk equiatomic FeCo. Although it is very difficult to quench the disordered state in bulk samples, the extreme cooling rates present in the plasma reactor produce metastable disordered nanoparticles. Neutron powder diffractograms acquired during a heating-cooling cycle at 27 degrees C, 710 degrees C, 800 degrees C, 710 degrees C, and 400 degrees C indicate the particles relax to their equilibrium ordered state upon first heating, disorder as they pass through the transformation temperature, and reorder upon cooling.

Citation

Applied Physics

Volume

85

Pub Type

Journals

Keywords

fine particle magnetism, magnetic nanoparticles, neutron diffraction, order-disorder transformation

Citation

Scott, J. , Chowdary, K. , Turgut, Z. , Majetich, S. and McHenry, M. (1999), Neutron Powder Diffraction of Carbon-Coated FeCo Alloy Nanoparticles, Applied Physics (Accessed April 26, 2024)