Are superparamagnetic spins classical?

Abstract

Effective giant spins of magnetic nanoparticles are considered classically in the conventional theory of superparamagnetism based on the Landau-Lifshitz-Langevin equation. However, microscopic calculations for a large spin with uniaxial anisotropy, coupled to the lattice via the simplest generic mechanism, show that the results of the conventional theory are not reproduced in the limit S ->\infty. In particular, the prefactor Gamma_0 in the Arrhenius escape rate over the barrier Gamma =Gamma_0 exp[-Delta U/(k_B T)] has an anomalously large sensitivity to symmetry-breaking interactions such as transverse field

6 EPL pages, 3 figure captions

References in corpus (7)

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