Quenched Spin Tunneling and Diabolical Points in Magnetic Molecules: II. Asymmetric Configurations

Abstract

The perfect quenching of spin tunneling first predicted for a model with biaxial symmetry, and recently observed in the magnetic molecule Fe_8, is further studied using the discrete phase integral (or Wentzel-Kramers-Brillouin) method. The analysis of the previous paper is extended to the case where the magnetic field has both hard and easy components, so that the Hamiltonian has no obvious symmetry. Herring's formula is now inapplicable, so the problem is solved by finding the wavefunction and using connection formulas at every turning point. A general formula for the energy surface in the vicinity of the diabolo is obtained in this way. This formula gives the tunneling apmplitude between two wells unrelated by symmetry in terms of a small number of action integrals, and appears to be generally valid, even for problems where the recursion contains more than five terms. Explicit results are obtained for the diabolical points in the model for Fe_8. These results exactly parallel the experimental observations. It is found that the leading semiclassical results for the diabolical points appear to be exact, and the points themselves lie on a perfect centered rectangular lattice in the magnetic field space. A variety of evidence in favor of this perfect lattice hypothesis is presented.

Revtex; 4 ps figures; follow up to cond-mat/0003114

References in corpus (5)

• Tunnel splittings for one dimensional potential wells revisited
• Diabolical Points in Magnetic Molecules: An Exactly Solvable Model
• Oscillatory Tunnel Splittings in Spin Systems: A Discrete Wentzel-Kramers-Brillouin Approach
• Quenched Spin Tunneling and Diabolical Points in Magnetic Molecules: II. Asymmetric Configurations
• Diabolical points in the magnetic spectrum of Fe_8 molecules

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• Quenched Spin Tunneling and Diabolical Points in Magnetic Molecules: II. Asymmetric Configurations
• Geometric-phase interference in a Mn_{12} single-molecule magnet with four-fold rotational symmetry
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