Helicity of magnetic domains in holmium studied with circularly polarized x rays

We have studied the helicity of magnetic domains in antiferromagnetic holmium using circularly polarized x rays. The spiral magnetic structure of holmium gives rise to pairs of magnetic satellites split symmetrically around each of the main charge Bragg reflections. For circularly polarized Light the nonresonant scattering amplitudes at these satellites depend upon the helicity of the spiral, and thereby yield information about the distribution of magnetic domains with opposite helicity in the sample. The high degree of circular polarization (96%) in the incident beam was obtained by transforming a linearly polarized undulator beam with the help of a diamond quarter-wave plate. The data reveal that domains with opposite helicity were nearly equally distributed in the crystal under investigation.