Phase interference of spin tunneling in an arbitrarily directed magnetic   field
  We present an exact analytic study on the topological phase interference effect in resonant quantum tunneling of the magnetization between degenerate excited levels for biaxial ferromagnets in an arbitrarily directed magnetic field. We show that the topological phase interference effect depends on the orientation of the field distinctly. The transition from classical to quantum behavior is also discussed. 
Rong Lu, Jia-Lin Zhu, Yi Zhou, and Bing-Lin Gu (Center for Advanced   Study, Tsinghua University, Beijing, P. R. China)