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 Ba{sub 2}CuGe{sub 2}O{sub 7}. 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. {copyright} {ital 1999} {ital The American Physical Society}