Cycloidal order of 4f moments as a probe of chiral domains in DyMnO₃.

Using soft x-ray diffraction at the Dy-M₅ resonance, pronounced circular dichroism in the ferroelectric phase of DyMnO₃ is observed in connection with sizable b and c components of the Dy-4f magnetic moments. This provides strong evidence for cycloidal order of the 4f moments, corroborating that inversion-symmetry breaking in this material is not accomplished by the Mn spins alone. The 4f circular dichroism allows us to image multiferroic domains that are imprinted on the surface of DyMnO₃ using the local charging by the x-ray beam via the photoelectric effect.