Polarized neutron scattering experiments have demonstrated that $\mathrm{Dy}/\mathrm{Y}$ multilayer structures possess a coherent spin helix with a preferable chirality induced by the magnetic field. The average chirality, being proportional to the difference in the left- and right-handed helix population numbers, is measured as a polarization-dependent asymmetric part of the magnetic neutron scattering. The magnetic field applied in the plane of the sample upon cooling below $T_N$ is able to repopulate the otherwise equal population numbers for the left- and right-handed helixes. The experimental results strongly indicate that the chirality is caused by Dzyaloshinskii-Moriya interaction due to the lack of the symmetry inversion on the interfaces.

• Received 23 December 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.197203