Order-Disorder Transition of a Two-Dimensional Spin 1/2 Heisenberg Antiferromagnet with Nonmagnetic Impurities.

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  • Yasuda Chitoshi
    Department of Physics, Faculty of Science and Technology, Science University of Tokyo, Noda, Chiba 278
  • Oguchi Akihide
    Department of Physics, Faculty of Science and Technology, Science University of Tokyo, Noda, Chiba 278

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タイトル別名
  • Order-Disorder Transition of a Two-Dime

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説明

Considering the reduction effect of the number of magnetic atoms and using Kondo and Yamaji's method and the coherent potential approximation, we investigate magnetic properties of a spin 1/2 Heisenberg antiferromagnet with nonmagnetic impurities on a square lattice. It is found that the critical impurity concentration xc is different from the percolation threshold xp in the ground state. The ground state changes from the Néel ordered state to a disordered state at xc~= 0.07. The coherent exchange integral Jp vanishes at xp~= 0.56. For 0≤ x<xc the system is in the ordered state and for xc<x<xp in the disordered state. This disordered state is characterized by the finite Jp and energy gap and the exponentially decaying correlation function. This result explains that the reduction rate of the Néel temperature of Mg-doped La_2CuO_4 is larger than that of K_2CoF_4 and K_2MnF_4. The uniform susceptibility as a function of temperature and concentration is obtained.

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