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Factorized Ground State and Magnetic Properties of Ferrimagnets

Rezai, Mohammad | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39643 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Langari, Abdollah
  7. Abstract:
  8. The anisotropic Heisenberg ferrimagnet which is composed of two different kind of spins is studied. We have found the exact (factorized) ground state of a general class of ferrimagnets in the presence of a magnetic field which includes the frustrated, anisotropic and long range interactions for arbitrary dimensional space. The factorized ground state is a product of single particle kets on a bipartite lattice composed of two different spins (σ, ρ) which is characterized by two angles, a bi-angle state. The spin waves analysis around the exact ground state show two branch of excitations which is the origin of two dynamics of the model. The signature of these dynamics is addressed as a peak and a broaden bump in the specific heat. We have finally focused our attention on the anisotropic Heisenberg chain. We have found the magnetic properties of the ferrimagnetic XXZ chain. We have applied the spin wave theory around different classical states. If the classical ground state is considered as the Neel state of the model the spin wave theory is valid only as far as the magnetic field is smaller than a fixed value (h1). Moreover, if we consider a ferromagnetic-type classical state which is reasonable for a saturated phase the spin wave theory will be valid as far as the magnetic field is greater than h2. In both case we can not get knowledge about the region between h1
  9. Keywords:
  10. Ferrimagnetic ; Factorized State ; Anisotropic Heisenberg Model

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