Microscopic Theory for the Markovian Decay of Magnetization Fluctuations in Nanomagnets

Abstract

We present a microscopic theory for the phonon-driven decay of the magnetization fluctuations in a wide class of nanomagnets where the dominant energy is set by isotropic exchange and/or uniaxial anisotropy. Based on the Zwanzig-Mori projection formalism, the theory reveals that the magnetization fluctuations are governed by a single decay rate ${\omega }_c$, which we further identify with the zero-frequency portion of the associated self-energy. This dynamical decoupling from the remaining slow degrees of freedom is attributed to a conservation law and the discreteness of the energy spectrum, and explains the omnipresent mono-exponential decay of the magnetization over several decades in time, as observed experimentally. A physically transparent analytical expression for ${\omega }_c$ is derived which highlights the three specific mechanisms of the slowing down effect which are known so far in nanomagnets.

arXiv comment7 pages

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Cited by in corpus (2)

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• Theory of severe slowdown in the relaxation of rings and clusters with antiferromagnetic interactions