Phase transition between quantum and classical regimes for the escape rate of a biaxial spin system

TL;DR

This paper investigates the transition between quantum and classical escape regimes in a biaxial spin system, highlighting how anisotropy and magnetic fields influence the phase boundary and crossover temperature.

Contribution

It introduces a particle Hamiltonian for the spin system and analyzes the nature of phase transitions depending on anisotropy and magnetic field parameters.

Findings

Phase boundary is affected by transverse anisotropy.

Crossover temperature depends on external magnetic field.

Transition order varies with system parameters.

Abstract

Employing the method of mapping the spin problem onto a particle one, we have derived the particle Hamiltonian for a biaxial spin system with a transverse or longitudinal magnetic field. Using the Hamiltonian and introducing the parameter $p (\equiv (U_{max}-E)/(U_{max}-U_{min}))$ where $U_{max}$ (U_{min}) corresponds to the top (bottom) of the potential and $E$ is the energy of the particle, we have studied the first- or second-order transition around the crossover temperature between thermal and quantum regimes for the escape rate, depending on the anisotropy constant and the external magnetic field. It is shown that the phase boundary separating the first- and second-order transition and its crossover temperature are greatly influenced by the transverse anisotropy constant as well as the transverse or longitudinal magnetic field.