THE ANISOTROPIC FIRST-NEIGHBOR CONTRIBUTION TO THE HYPERFINE FIELD INHEXAGONAL-CLOSE-PACKED CO - A NUCLEAR-MAGNETIC-RESONANCE STUDY OF DILUTED ALLOYS AND MULTILAYERS

Co-59 NMR has been studied in CoCr, CoRu, CoMn and CoCu hexagonal allo ys with impurity concentrations below 1 at.% and in two-dimensional al loys present at the interfaces of the corresponding Co/M multilayers, where Co adopts the hcp structure. Two low-frequency satellites have b een observed for all of the alloys studied, whereas only one is observ ed for cubic alloys. Their origin is related to the presence of two in equivalent sites in the first coordination shell of Co, because hcp Co departs from the ideal compact structure. From the results on Co/Cr a nd Co/Ru multilayers it is deduced that the impurity neighbours out of the c-plane depress the Co hyperfine field less than the in-plane imp urity neighbours. Comparison with the alloys CoCr and CoRu suggests a similar conclusion for CoMn alloys. As to CoCu systems, the situation is the opposite, although there is some ambiguity in the analysis of h cp Co/fcc Cu multilayers, because Co might be stacked in a fee structu re at the interface with Cu.