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Paper   IPM / P / 12036
School of Physics
  Title:   Phase Diagram of the XXZ Ferrimagnetic Spin-(1/2, 1) Chain in the Presence of Transverse Magnetic Field
1.  A . Langari
2.  J . Abouie
3.  M.Z. Asadzadeh
4.  M. Rezai
  Status:   Published
  Journal: J.Stat. Mech: Theory and Experiments
  Vol.:  august 2011
  Year:  2011
  Pages:   p08001-p08007
  Publisher(s):   IOP Publishing Ltd and SISSA
  Supported by:  IPM
We investigate the phase diagram of an anisotropic ferrimagnetic spin-(1/2, 1) in the presence of a non-commuting (transverse) magnetic field. We find a magnetization plateau for the isotropic case while there is no plateau for the anisotropic ferrimagnet. The magnetization plateau can appear only when the Hamiltonian has the U(1) symmetry in the presence of the magnetic field. The anisotropic model is driven by the magnetic field from the N?eel phase for low fields to the spin-flop phase for intermediate fields and then to the paramagnetic phase for high fields. We find the quantum critical points and their dependence on the anisotropy of the aforementioned field-induced quantum phase transitions. The spin-flop phase corresponds to the spontaneous breaking of Z2 symmetry. We use the numerical density matrix renormalization group and analytic spin wave theory to find the phase diagram of the model. The energy gap, sublattice magnetization and total magnetization parallel and perpendicular to the magnetic field are also calculated. The elementary excitation spectra are obtained via the spin wave theory in the three different regimes depending on the strength of the magnetic field.

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