Polarized-Neutron-Diffraction Study of Magnetic Moments in Yttrium-Cobalt Alloys

The magnetic moments in the ordered Y${\mathrm{Co}}_5$, ${\mathrm{Y}}_2$ ${\mathrm{Co}}_7$, and Y${\mathrm{Co}}_3$ intermetallic compounds with closely related crystal structures have been investigated on single crystals using the polarized-neutron-diffraction technique. By assuming that only the cobalt atoms have magnetic moments and using Moon's experimental cobalt form factor extrapolated smoothly to unity, a discrepancy was found between the measured and calculated magnetic-structure factors. This can be explained by the existence of either a magnetic moment at the yttrium sites coupled antiparallel to the cobalt moments, or a diffuse negative-spin polarization. In the present study, it is not possible to decide between the two models. The ferromagnetically aligned magnetic moments on the cobalt atoms are influenced by the yttrium neighbors; they are the smallest in Y${\mathrm{Co}}_3$, which is the richest in yttrium, and in all cases are the smallest at the sites having the most yttrium neighbors.