Net Dzyaloshinskii-Moriya interaction in defect-enriched ferromagnet.

The Dzyaloshinskii-Moriya interaction (DMI), which typically occurs in lattices without space inversion symmetry, can also be induced in a highly symmetric lattice by local symmetry breaking due to any lattice defect. We recently presented an experimental study of polarized small angle neutron scattering (SANS) on the nanocrystalline soft magnet Vitroperm (Fe73Si16B7Nb3Cu1), where the interface between the FeSi nanoparticles and the amorphous magnetic matrix serves as such a defect. The SANS cross sections exhibited the polarization-dependent asymmetric term originating from the DMI. One would naturally expect the defects characterised by a positive and a negative DMI constant D to be randomly distributed and this DMI-induced asymmetry to disappear. Thus, the observation of such an asymmetry indicates that there exists an extra symmetry breaking. In the present work we experimentally explore the possible causes by measuring the DMI-induced asymmetry in the SANS cross sections of the Vitroperm sample tilted in different directions with respect to the external magnetic field. Furthermore, we analyzed the scattered neutron beam using a spin filter based on polarized protons and confirm that the asymmetric DMI signal originates from the difference between the two spin-flip scattering cross-sections. .