NMR and Magnetic Studies of Mechanically Alloyed Co30M70(M=Cu, Ag, Au)

Abstract

Zero-field 59 Co NMR, X-ray diffraction (XRD) and magnetization measurements have been made to investigate the mechanical alloying (MA) of ferromagnetic Co 30 M 70 (M=Cu, Ag and Au) powder as a function of milling time (MT). The MA in Co 30 Cu 70 proceeds rapidly with increasing MT by both the processes of dissolving Cu in the Co matrix and Co in the Cu matrix and is nearly completed for MT=100 h. In Co 30 Ag 70 the MA hardly proceeds even for MT=300 h or more. The MA in Co 30 Au 70 proceeds much more slowly than that in Co 30 Cu 70 with increasing MT up to 150 h and takes place rapidly for MT≈200 h. The magnetizations and NMR spectra of the Co 30 Cu 70 and Co 30 Au 70 samples for MT=200 h are similar to each other, indicating that both the samples form similar supersaturated alloys. NMR results of the Co 30 M 70 samples milled for MT=200 h show large spin fluctuations of Co atoms, which are due to fine sizes of clusters, suggesting that the samples milled for long times consist of nanometer-size clusters.