Spin-dynamics simulation study of the field-induced phase transition for the spiral antiferromagnet Ba2CuGe2O7

We perform spin-dynamics SD simulations to study the field induced incommensurate-to-commensurate phase transition for the spiral antiferromagnet Ba2CuGe2O7. Under an increasingly applied magnetic field, we find that the system undergoes a transition from a two-dimensional 2D spiral state to a spin-flop state, passing through an intermediate phase. The simulations identify two order parameters to characterize this phase transition, of which one is the spiral period known previously, another is the root-mean-square value of a spin component. For the 2D spiral phase identified previously, our SD simulations yield essentially the same spin structures as previous continuum-field model studies when the applied field is very small, but quantitative differences exist when the field is not small. For the intermediate phase which was not fully understood by previous studies, our simulations reveal that its spin structure is a soliton-like state consisting of two spin-flop states connected by a three-dimensional spiral state.