Microscopic theory for the Markovian decay of magnetization fluctuations in nanomagnets

Ioannis Rousochatzakis

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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 ωc, 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 monoexponential decay of the magnetization over several decades in time, as observed experimentally. A physically transparent analytical expression for ωc is derived which highlights the three specific mechanisms of the slowing-down effect which are known so far in nanomagnets.

Original languageEnglish (US)
Article number214431
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume76
Issue number21
DOIs
StatePublished - Dec 27 2007

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