A compositionally inhomogeneous state in electroless-deposited CoNiP films with perpendicular magnetic anisotropy is investigated using spin-echo 59Co nuclear magnetic resonance (NMR), focusing on its correlation with magnetic properties. By adjusting pH of the electroless-deposition bath, films were prepared which possess almost the same average composition (Co42Ni50P8) and crystal orientation, but the differing values of coercivity (Hc). By analyzing the shift in peak resonance frequency of NMR spectra of the CoNiP films with respect to that of bulk CoNi alloys, we observed the formation of a compositionally inhomogeneous state in the film which possesses high Hc of 2600 Oe, whereas formation of inhomogeneities was not observed for the low-Hc films. By assuming that a Co-enriched ferromagnetic component detected by NMR was separated from a non-magnetic amorphous Ni-P component, we found that the high-Hc film consists of Co42Ni26 and Ni24P8. Moreover, the results of high spatial resolution X-ray microanalysis on the high-Hc film showed a tendency that the Co-enriched ferromagnetic component segregates to the center of grains and the Ni-P non-magnetic component segregates to grain boundaries. Such evidence indicates that compositional inhomogeneities could be one of the origins of high-Hc in CoNiP films.
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