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The Non--Ergodicity Threshold: Time Scale for Magnetic Reversal

G. L. Celardo·J. Barre·F. Borgonovi·S. Ruffo
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Abstract

We prove the existence of a non-ergodicity threshold for an anisotropic classical Heisenberg model with all-to-all couplings. Below the threshold, the energy surface is disconnected in two components with positive and negative magnetizations respectively. Above, in a fully chaotic regime, magnetization changes sign in a stochastic way and its behavior can be fully characterized by an average magnetization reversal time. We show that statistical mechanics predicts a phase--transition at an energy higher than the non-ergodicity threshold. We assess the dynamical relevance of the latter for finite systems through numerical simulations and analytical calculations. In particular, the time scale for magnetic reversal diverges as a power law at the ergodicity threshold with a size-dependent exponent, which could be a signature of the phenomenon.

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G. L. Celardo, J. Barre, F. Borgonovi, S. Ruffo. 2005-07-28. The Non--Ergodicity Threshold: Time Scale for Magnetic Reversal. https://doi.org/10.1103/physreve.73.011108

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