Magnetization-plateau state of the S=3/2 spin chain with single-ion anisotropy

We reexamine the numerical study of the magnetized state of the S=3/2 spin chain with single-ion anisotropy D(>0) for the magnetization M=M-S/3, where M-S is the saturation magnetization. At this magnetization we find that for D<D-c1 = 0.387 the system is critical and the magnetization plateau does not appear. For D>D-c1. the parameter region is divided into two parts D-cl<D<D-c2=0.943 and D-c2<D. In each region, the system is gapful and the M=M-S/3 magnetization plateau appears in the magnetization process. From our numerical calculation, the intermediate region D-cl<D<D-c2 should be characterized by a magnetized valence-bond-solid state.