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 \cal H= -DS_z^2 - H_zS_z + B S_x^2 is investigated by a perturbative approach with respect to B [D. A. Garanin, J. Phys A {\bf 24}, L61 (1991)]. The transition is first order for B<B_c(H_z), the boundary line going to zero as B_c/D ~ 1 - H_z/(2SD) in the strongly biased limit. The range of the first-order transition is thus larger than for the model \cal H = -DS_z^2 - H_zS_z - H_x S_x studied earlier, where in the strongly biased case H_{xc}/(2SD) ~ [1-H_z/(2SD)]^{3/2}. The temperature of the quantum-classical transition, T_0, behaves linearly in the strongly biased case for both models: T_0 ~ 2SD - H_z.

4 PR pages, 5 figures, submitted to PRB

References in corpus (4)

• Thermally Activated Resonant Magnetization Tunneling in Molecular Magnets: Mn_12Ac and others
• First- and Second-Order Transitions between Quantum and Classical Regimes for the Escape Rate of a Spin System
• Quantum-Classical Transition of the Escape Rate of a Uniaxial Spin System in an Arbitrarily Directed Field
• Periodic Instantons and Quantum-Classical Transitions in Spin Systems

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