Quantum-classical phase transition of escape rate in biaxial spin system with an arbitrarily directed magnetic field

Abstract

We investigate the escape rate of a biaxial spin particle with an arbitrarily dierected magnetic field in the easy plane, described by Hamiltonian $\mathcal{H}=-A{S}_z^2-B{S}_x^2-H_x{S}_x-H_z{S}_z,(A>B>0)$. We derive an effective particle potential by using the method of particle mapping. With the help of the criterion for the presence of a first-order quantum-classical transition of the escape rate we obtained various phase boundary curves depending on the anisotropy parameter $b\equiv B/A$ and the field parameters ${\alpha }_{x,z}\equiv H_{x,z}/AS$ : ${\alpha }_{zc}(b_c{)}^{\prime }s,{\alpha }_{xc}(b_c{)}^{\prime }s$, and ${\alpha }_{zc}={\alpha }_{zc}({\alpha }_{xc})$. It is found from ${\alpha }_{zc}(b_c{)}^{\prime }s$ and ${\alpha }_{xc}(b_c{)}^{\prime }s$ that the-first-order region decreases as $b$ and ${\alpha }_x$ (or ${\alpha }_z$) increase. The phase boundary line ${\alpha }_{zc}={\alpha }_{zc}({\alpha }_{xc})showsthatcomparedwiththeuniaxialsystem,boththefirst-andsecond-oredrregionsarediminishedduetothetransverseanisotropy.Moreover,itisobservedthat,inthelimit$α_{xc} \to 0$,$α_{zc}$doesnotcoinsideswiththecoercivefieldline,whichyieldsmorereductioninthefirst-orderregion.Wehavealsocomputedthecrossovertemperaturesatthephaseboundary:$T_c(b_c), T_c(α_{xc}, α_{zc})$.

17pages, 8figures

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Cited by in corpus (4)

• Macroscopic quantum tunneling and quantum-classical phase transitions of the escape rate in large spin systems
• Phase transition between quantum and classical regimes for the escape rate of dimeric molecular nanomagnets in a staggered magnetic field
• Quantum-classical transition of the escape rate of a biaxial ferromagnetic spin with an external magnetic field
• Quantum-classical phase transition of the escape rate of two-sublattice antiferromagnetic large spins