  The square-lattice antiferromagnet Ba2CoGe2O7 is studied by means of neutron
diffraction and inelastic scattering. This material is isostructural to the
well-known Dzyaloshinskii-Moriya helimagnet Ba2CuGe2O7, but exhibits
commensurate long-range Neel order at low temperatures. Measurements of the
spin wave dispersion relation reveal strong in-plane anisotropy that is the
likely reason for the suppression of helimagnetism.
