Search for Noncollinear Spin Density in Hexagonal Co

Abstract

The interpretation of the magnetic form factors for the 3d metals has been based on the assumption that the magnetic moment is everywhere collinear, so that a scalar density function may be used. Blume1 has pointed out that if the spin density is noncollinear, the form factor measurements should be reinterpreted. Using the new technique of neutron polarization analysis, we have seen no evidence for scattering due to a noncollinear component of the spin density in hexagonal cobalt. Upper limits on the magnitude of such scattering have been established for the (002) and (110) reflections. Further, it can be shown that the polarized beam technique used in the form-factor measurements is not very sensitive to a small noncollinear spin component. Ignoring the presence of noncollinear spin scattering, of magnitude given by the upper limit of the polarization analysis experiment, produces an error in the Co form factor smaller than the experimental error due to other effects. For the cases of Fe and Ni, the noncollinear spin density would have to be much larger than the upper limit in Co to have any influence on the form-factor measurements. We conclude that the noncollinear spin density in hexagonal cobalt is zero within our limits of detection and, further, that it is highly improbable that a noncollinear spin density could exist in Fe or Ni large enough to affect any of the conclusions which have been drawn from the form-factor measurements.