Phase diagram of the Dzyaloshinskii-Moriya helimagnet Ba2CuGe2O7in canted magnetic fields

Abstract

The evolution of different magnetic structures of noncentrosymmetric Ba${}_{2}$CuGe${}_{2}$O${}_{7}$ is systematically studied as a function of the orientation of the magnetic field $\mathbit{H}$. Neutron diffraction in combination with measurements of magnetization and specific heat show a virtually identical behavior of the phase diagram of Ba${}_{2}$CuGe${}_{2}$O${}_{7}$ for $\mathbit{H}$ confined in both the (1,0,0) and (1,1,0) plane. The existence of a recently proposed incommensurate double-$k$ AF-cone phase is confirmed in a narrow range for $\mathbit{H}$ close to the tetragonal $c$ axis. For large angles enclosed by $\mathbit{H}$ and the $c$ axis, a complexly distorted nonsinusoidal magnetic structure has recently been observed. We show that its critical field ${H}_{c}$ systematically increases for larger canting. Measurements of magnetic susceptibility and specific heat finally indicate the existence of an incommensurate/commensurate transition for $\mathbit{H}\ensuremath{\approx}9\mathrm{T}$ applied in the basal $(a,b)$ plane and agree with a nonplanar, distorted cycloidal magnetic structure.