2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/99254We 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.4 pages, 8 figures, revised version, to appear in J.Phys.Soc.JpnStatistical MechanicsStrongly Correlated Electronstext