Interplay Of Rkky, Zeeman, And Dzyaloshinskii-Moriya Interactions And The Nonzero Average Spin Chirality In Dy/Y Multilayer Structures

Metal magnetic/nonmagnetic (Dy/Y) multilayer structures posses a coherent spin helix propagating through many Dy/Y bilayers. Samples of different Dy and Y layer thicknesses were investigated using polarized neutron scattering to determine the average chirality of the magnetic structure. The in-plane applied magnetic field induces the chirality since it couples to the uncompensated moments of the helix in a Dy layer. The value of the chirality has a complex behavior in dependence on the temperature and the magnetic field. It is shown that the chirality is affected by the competition between the Ruderman-Kittel-Kasuya-Yoshida interactions of the intralayer exchange within the Dy layers and the interlayer coupling across the nonmagnetic Y layers. The set of the experimental data allows one to make the reconstruction and schematic visualization of the spin structure within the multilayer system. In spite of a complex dependency of the average chirality on the temperature and the magnetic field, the twist angle between the spin planes of two neighboring Y/Dy interfaces has the same sign for all samples at any conditions. It is antisymmetric Dzyaloshinsky-Moriya interaction that reveals itself through the sign of this twist angle and as a result through the nonzero average chirality of the magnetic multilayer structure.