An Extended Effective Potential Method with Topological Phase of Spin Tunneling

An extended effective potential (EEP) method is proposed to calculate the spin tunneling splitting of a single-domain ferromagnetic grain. By adding a phase factor to replace the boundary condition, the new method is not only accurate but also shows topological effects. In the large spin limit, the results from spin-coherent-state path integral have systematic disparity with numerical studies, while those from the EEP method agree well with numerical studies.