Magnetic reversal time in open long-range systems

Abstract

Topological phase space disconnection has been recently found to be a general phenomenon in many-body spin system with anisotropic interaction. We show that the power law divergence of magnetic reversal time at the energy signaling such disconnection is generic for long-range interacting systems with an exponent proportional to the number of particles. We also study the modifications induced putting the system in contact with a thermal bath. Using the canonical formalism we analyze the magnetic reversal times at any temperature. Moreover, due to the divergence of reversal time at the energy disconnection threshold we can recover, using saddle point approximation, a simple exponential dependence on the inverse temperature showing the explicit relevance of the energy disconnection threshold for finite many-body interacting systems at finite temperature. This sets a general framework to understand the emergence of ferromagnetism in finite magnetic systems starting from microscopic models without phenomenological on-site barriers.

Enhancement of the magnetic anisotropy barrier in critical long range spin systems

“…where, τ 0 is a factor, that may depend on temperature too, E min is the ground state energy and β = 1/k B T . While this was confirmed in simple toy models with allto-all interaction among the spins [21], here our aim is to generalize these results to realistic spin systems. It is possible to give a heuristic justification of Eq.…”

“…In order to estimate the anisotropic energy barrier, we propose a different point of view which does not assume the specific motion of the spins upon the magnetic reversal; rather we estimate the minimal energy barrier that must be encountered during the magnetic reversal process. We related the energy barrier to the recently found topological non-connectivity threshold (TNT) in anisotropic spin systems [18][19][20][21].…”

Dynamics of random dipoles: chaos versus ferromagnetism

“…As shown in Ref. [23], the ergodicity breaking threshold can induce very large demagnetization times thus producing ferromagnetic behavior in finite samples. Thus, even if one would expect that invariant tori will be destroyed under a suitable thermal perturbation, the question on the demagnetization times in presence of temperature and on the relevance of the ergodicity breaking is still open.…”