Thermal entanglement of two interacting qubits in a static magnetic field G. Lagmago Kamta, A. Y. Istomin and A. F. Starace Eur. Phys. J. D, 44 2 (2007) 389-400 Published online: 22 June 2007 DOI: 10.1140/epjd/e2007-00207-5