The polarization dependence of Bragg diffraction in magnetic materials, coupled to microfocussing
optics, allows imaging of magnetic domains through diffraction contrast. In spiral antiferromagnets,
for example, the moments align ferromagnetically within an atomic layer but rotate by a characteristic angle
between successive layers (left panel). Spirals of either handedness can occure, resulting in the formation
of chiral magnetic domains in the sample. This magnetic super structure yields satellite peaks on either side
of charge Bragg peaks; i.e., at (0,0,L±τ) (right panel). At these peaks, circularly polarized x-rays
are sensitive to the handedness of the spiral. So an image of the chiral domains can be obtained by
measuring the difference in the Bragg scattering for alternate helicities as the sample is scanned across
the beam. Two 600x450µm2 domain images taken on a Ho metal sample at the ±τ magnetic peaks
exhibit the same domain structure with reversed contrast, as expected. [J. Appl. Phys., 95, 6357 (2004)].
Local Contact: Jonathan Lang (
lang@aps.anl.gov)
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