Magnetic phase diagram of the S=1/2 antiferromagnetic zigzag spin chain   in the strongly frustrated region: cusp and plateau
  We determine the magnetic phase diagram of the antiferromagnetic(AF) zigzag spin chain in the strongly frustrated region, using the density matrix renormalization group method. We find the magnetization plateau at 1/3 of the full moment accompanying the spontaneous symmetry breaking of the translation, the cusp singularities above and/or below the plateau, and the even-odd effect in the magnetization curve. We also discuss the formation mechanisms of the plateau and cusps briefly. 
Kouichi Okunishi and Takashi Tonegawa