Abstract
The escape rate of the large-spin model described by the Hamiltonian is investigated with the help of the mapping onto a particle moving in a double-well potential . The transition-state method yields in the moderate-damping case as a Boltzmann average of the quantum transition probabilities. We have shown that the transition from the classical to quantum regimes with lowering temperature is of the first order discontinuous at the transition temperature for below the phase boundary line , where , and of the second order above this line. In the unbiased case the result is , i.e., one fourth of the metastability boundary , at which the barrier disappears. In the strongly biased limit , one has , which is about one half of the boundary value . The latter case is relevant for experiments on small magnetic particles, where the barrier should be lowered to achieve measurable quantum escape rates.
- Received 19 November 1997
DOI:https://doi.org/10.1103/PhysRevB.57.13639
©1998 American Physical Society