Enhancement of thermal entanglement in two-qubit XY models
  We analyze conditions leading to enhancement of thermal entanglement in two-qubit XY models. The effect of including cross-product terms, besides the standard XY exchange interactions, in the presence of an external magnetic field, is investigated. We show that entanglement can be yield at elevated temperatures by tuning the orientation of the external magnetic field. The details of the intrinsic exchange interactions determine the optimal orientation. 
Celia Anteneodo and Andre M.C.Souza