Solubility extension and phase formation in gas-condensed Co–W nanoclusters

Authors

Farhad Golkar, University of Nebraska-LincolnFollow
Matthew J. Kramer, Ames Laboratory, USDOEFollow
Ames Laboratory, Ames Laboratory
Ralph A. Skomski, University of Nebraska-LincolnFollow
David J. Sellmyer, University of Nebraska-LincolnFollow
Jeffrey E. Shield, University of Nebraska-LincolnFollow

Date of this Version

2013

Citation

Journal of Nanoparticle Research 15:1638 (April 2013)

Abstract

Co–W alloy clusters with extended solubility of W in hcp Co were produced by inert-gas condensa-tion. The structural state of the as-deposited Co–W clusters was found to be critically dependent on processing parameters such as the cooling scheme and sputtering power. For the water-cooled clus-ters, the mean size and percent crystalline were strongly dependent on sputtering power, while the percent crystalline of the liquid nitrogen-cooled clusters was not as affected by the sputtering power. At low sputtering powers, the water-cooled clusters were predominantly amorphous, but became increasingly more crystalline as the sputtering power increased. The predominant crystalline phase was hcp Co(W), but high-resolution transmission electron microscopy revealed that very small and very large clusters contained fcc and Co₃W structures, respectively. For liquid nitrogen cooling the clusters were predominantly amorphous regardless of sputtering power, although at the highest sputtering power a small percentage of the clusters were crystalline. The magnetic properties were dependent on cooling schemes, sputtering power, and temperature, with the highest coercivity of 893 Oe obtained at 10 K for water-cooled clusters sputtered at 150 W. The magnetocrystalline anisot-ropy of the water-cooled sample increased with increasing sputtering power, with the highest ani-sotropy of 3.9 × 10⁶ ergs/cm³ recorded for clusters sputtered at 150 W. For liquid nitrogen-cooled samples, the anisotropy was approximately constant for all sputtering powers.