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Paper   IPM / Physic / 6619
School of Physics
  Title:   Phase Diagram of the Antiferromagnetic XXZ Model in the Presence of An External Magnetic Field
  Author(s):  A. Langari
  Status:   Published
  Journal: Phys. Rev. B
  No.:  48
  Vol.:  58
  Year:  1998
  Pages:   14467-14475
  Supported by:  IPM
The anisotropic s=[1/2] anti-ferromagnetic Heisenberg chain in the presence of an external magnetic field is studied by using the standard quantum renormalization group. We obtain the critical line of the transition from partially magnetized (PM) phase to the saturated ferromagnetic (SFM) phase. The crossover exponent between the PM phase and anti-ferromagnetic Ising (AFI) phase is evaluated. Our results show that the anisotropy (∆) term is relevant and causes crossover. These results indicate that the standard RG approach yiels fairly good values for critical points and their exponents. The magnetization curve, correlation functions and the ground state energy per site are obtained and compared with the known exact results.

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