The Entanglement in Anisotropic Heisenberg XYZ Chain with inhomogeneous   magnetic field
  The thermal entanglement of a two-qubit anisotropic Heisenberg $XYZ$ chain under an inhomogeneous magnetic field b is studied. It is shown that when inhomogeneity is increased to certain value, the entanglement can exhibit a larger revival than that of less values of b. The property is both true for zero temperature and a finite temperature. The results also show that the entanglement and critical temperature can be increased by increasing inhomogeneous exteral magnetic field. 
G.H. Yang, W.B. Gao, L. Zhou, H.S.Song