Nuclear Resonance Study of Hyperfine Fields in Nickel-Rich Nickel-Cobalt Alloys

Abstract

The nuclear-magnetic-resonance line shapes of ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ and ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$ have been studied in Ni-Co alloy powders, using the free-precession method, by plotting the amplitude of the spin-echo signal across the inhomogeneously broadened lines. The ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ nuclear resonance has been studied in the concentration range from 1 to 41.2 at.% cobalt and the ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$ from 1 to 14.8% cobalt. Both ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ resonance frequencies increase roughly linearly with increasing cobalt concentration. The higher concentration ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ studies were made at 77°K, while the low-concentration ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ studies and the ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$ studies were made at 4°K. Well-resolved satellite structure is observed. A line is observed approximately 10 MHz above the resonance frequency appropriate to dilute ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ in nickel. This line is believed due to cobalt atoms with one cobalt neighbor in the nearestneighbor shell. A similar line is observed in the ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ni}$ case approximately 5 MHz above the pure-nickel resonance frequency. A discussion of the relation between hyperfine fields and local atomic moments is made, and it is concluded that the conduction-electron polarization is a major contribution to the hyperfine fields in these alloys. An oscillatory variation of the spin density about the solute atoms is indicated and appears to explain the observed spectra.