Thermal Entanglement in the Pure Dzyaloshinskii-Moriya Model with Magnetic Field

We investigate the effects of the directions of Dzyaloshinskii-Moriya (DM) interaction and magnetic field on the thermal entanglement in the pure DM model. It is found that when the Hamiltonian is H-1 = D center dot (sigma(1) circle times sigma(2)) + B center dot sigma(1), the entanglement can reach its maximum if the directions of the magnetic field and the DM vector are parallel. In addition, when the Hamiltonian is H-2 = D center dot (sigma(1) circle times sigma(2)) \ B center dot (sigma(1) \ sigma(2)), if the directions of the magnetic field and the DM vector are perpendicular in a high magnetic field, or their directions are parallel in a weak magnetic field, the entanglement can also reach its maximum. Thus the entanglement can be enhanced by adjusting the direction of the external magnetic field, and this is feasible within the current experimental technology.