Non-Kramers Freezing and Unfreezing of Tunneling in the Biaxial Spin Model
Abstract
The ground state tunnel splitting for the biaxial spin model in the magnetic field, H = -D Sx2 + E Sz2 - g μB Sz Hz, has been investigated using an instanton approach. We find a new type of spin instanton and a new quantum interference phenomenon associated with it: at a certain field, H2 = 2SE1/2(D+E)1/2/(g μB), the dependence of the tunneling splitting on the field switches from oscillations to a monotonic growth. The predictions of the theory can be tested in Fe8 molecular nanomagnets.
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