Quantum phase transition of entanglement in Heisenberg spin model with quantized field M.-M. He, C.-T. Xu, G. Chen and J.-Q. Liang Eur. Phys. J. D, 39 2 (2006) 313-320 Published online: 20 April 2006 DOI: 10.1140/epjd/e2006-00087-1