Escape rate of a biaxial nanospin system in a magnetic field : first- and second-order transition between quantum and classical regimes

TL;DR

This paper analyzes the escape rate of a biaxial nanospin system under a magnetic field, deriving an effective potential and phase boundary to understand the transition between quantum and classical regimes.

Contribution

It introduces the first analytical derivation of the effective particle potential and phase boundary for the biaxial nanospin system with an applied magnetic field.

Findings

Derived an analytical phase boundary line between first- and second-order transitions.

Obtained a complete phase diagram for the system.

Expressed the crossover temperature as a function of the applied field.

Abstract

We investigate the escape rate of the biaxial nanospin particle with a magnetic field applied along the easy axis. The model studied here is described by the Hamiltonian ${\cal H} = -AS_z^2 - BS_x^2 - HS_z, (A>B>0)$. By reducing this Hamiltonian to a particle one, we derive, for the first time, an effective particle potential for this model and find an analytical form of the phase boundary line between first- and second-order transitions, from which a complete phase diagram can be obtained. We also derive an analytical form of the crossover temperature as a function of the applied field at the phase boundary.