Structural, morphological, and magnetic study of nanocrystalline cobalt-copper powders synthesized by the polyol process
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K. M. Kemner Condensed Matter and Radiation Division, Naval Research Laboratory, Washington, DC 20375
P. E. Schoen Laboratory for Molecular Interfacial Interactions, Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, DC 20375
W.T. Elam Condensed Matter and Radiation Division, Naval Research Laboratory, Washington, DC 20375
A. Ervin Chemistry Division, Naval Research Laboratory, Washington, DC 20375
S. Keller, Y.D. Zhang, and J. Budnick Department of Physics, University of Connecticut, Storrs, Connecticut 06269
T. Ambrose Department of Physics, Johns Hopkins University, Baltimore, Maryland 21218 (Received 20 December 1994; accepted 6 March 1995)
Nanocrystalline CoxCu10o-x (4 *s x =s 49 at. %) powders were prepared by the reduction of metal acetates in a polyol. The structure of powders was characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), extended x-ray absorption fine structure (EXAFS) spectroscopy, solid-state nuclear magnetic resonance (NMR) spectroscopy, and vibrating sample magnetometry (VSM). As-synthesized powders were composites consisting of nanoscale crystallites of face-centered cubic (fee) Cu and metastable face-centered cubic (fee) Co. Complementary results of XRD, HRTEM, EXAFS, NMR, and VSM confirmed that there was no metastable alloying between Co and Cu. The NMR data also revealed that there was some hexagonal-closed-packed (hep) Co in the samples. The powders were agglomerated, and consisted of aggregates of nanoscale crystallites of Co and Cu. Upon annealing, the powders with low Co contents showed an increase in both saturation magnetization and coercivity with increasing temperature. The results suggested that during preparation the nucleation of Cu occurred first, and the Cu crystallites served as nuclei for the formation of Co.
I. INTRODUCTION Fine particles (0.1 fiva =s diameter =s 20 fim) have been widely used in metallurgical and ceramic processing, and electronics applications. Recently, increasing interest has been found in synthesizing and processing nanoscale particles. Materials consisting of particles or other structures with dimensions in the range of 1—100 nm are often referred to as nanostructured materials. Because of size confinement effects in these dimensions, as well as the presence of a significant volume fraction of interfaces, nanostructured materials a) Author
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to whom correspondence should be addressed. J. Mater. Res., Vol. 10, No. 6, Jun 1995
may exhibit properties different from or even better than those of the same materials made of larger particles.1 Many methods exist for the preparation of nanoscale particles,1 including vapor deposition, solid-state milling, and solution chemistry. Chemical routes of fabricating nanoscale particles2 have the following attractive features: (i) tailored design of materials at the molecular level, (ii) control of particle size and size distribution, (iii) stabilization of particles against undesi
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