Investigation of Nearest Neighbor Interactions in Nickel Substituted Cobalt Using 59Co IFNMR

Abstract

Co100-x Nix (x = 10, 20, 30, 40) alloys were synthesized via the chemical method by reducing nitrates of cobalt and nickel using hydrazine as a reducing agent. The proportion of solvents, ethanol, and water was maintained constant for all the samples in the series. The structure and morphology of the samples were examined based on X-Ray diffraction (XRD) data and Scanning Electron Microscope (SEM) images. From XRD it was evident that the system had a mixture of hexagonal close packed (hcp) and face centered cubic (fcc) phases. The amount of hcp phase in the composition gradually reduced as the concentration of nickel increased. The effect of substitution of nickel on cobalt was studied using a home built 59Co internal field nuclear magnetic resonance (IFNMR) spectrometer. Further, the saturation magnetization and hence magnetic field anisotropy values, obtained from M vs H loops, are found to vary with nickel concentration. The NMR results show a broadening of the NMR signals in comparison with the pure phase of cobalt. The NMR spectra and the number of peaks were assigned to possible cobalt-nickel neighbors, and the percentage of such combinations is interpreted in terms of the frequency and intensity of the peaks. This percentage of different nickel-cobalt combinations was compared with the random distribution obtained using the binomial distribution function. This comparison shows a clear trend compared to that analysed by the IFNMR experiment.