Quantum-Classical Escape-Rate Transition of a Biaxial Spin System with a Longitudinal Field: a Perturbative Approach
Abstract
The quantum-classical transition of the escape rate of the spin model H= -DSz2 - HzSz + B Sx2 is investigated by a perturbative approach with respect to B [D. A. Garanin, J. Phys A 24, L61 (1991)]. The transition is first order for B<Bc(Hz), the boundary line going to zero as Bc/D ~ 1 - Hz/(2SD) in the strongly biased limit. The range of the first-order transition is thus larger than for the model H = -DSz2 - HzSz - Hx Sx studied earlier, where in the strongly biased case Hxc/(2SD) ~ [1-Hz/(2SD)]3/2. The temperature of the quantum-classical transition, T0, behaves linearly in the strongly biased case for both models: T0 ~ 2SD - Hz.
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