The effect of anisotropy and external magnetic filed on the thermal   entanglement in a two-spin-qutrit system
  We study the thermal entanglement in a two-spin-qutrit system with anisotropy in the exchange coupling between two spins. We use the realignment criterion to distinguish the entangled states, and the negativity for measuring the entanglement in this system. We see that the anisotropy can provide an additional parameter for enhancing the entanglement. 
S.Y. Mirafzali, M. Sarbishaei