Magnetic anisotropy and low-energy spin waves in the dzyaloshinskii-Moriya spiral magnet Ba₂CuGe₂O₇

Neutron-diffraction and inelastic-scattering experiments are used to investigate in detail the field dependence of the magnetic structure and low-energy spin-wave spectrum of the Dzyaloshinskii-Moriya helimagnet Ba₂CuGe₂O₇. The results suggest that the previously proposed model for the magnetism of this compound (an ideal sinusoidal spin spiral, stabilized by isotropic exchange and Dzyaloshinskii-Moriya interactions) needs to be refined. Both recent and previously published data can be quantitatively explained by taking into account the Kaplan-Shekhtman-Entin-Wohlman-Aharony term, a special magnetic anisotropy term that was predicted to always accompany Dzyaloshinskii-Moriya interactions in insulators.