Spin dynamics and relaxation in the classical-spin Kondo-impurity model beyond the Landau-Lifschitz-Gilbert equation

The real-time dynamics of a classical spin in an external magnetic field and local exchange coupled to an extended one-dimensional system of non-interacting conduction electrons is studied numerically. Retardation effects in the coupled electron-spin dynamics are shown to be the source for the relax...

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Bibliographic Details
Published in:New journal of physics 2015-11, Vol.17 (11), p.113058
Main Authors: Sayad, Mohammad, Potthoff, Michael
Format: Article
Language:English
Subjects:
75.78.-n
75.78.Jp
Conduction electrons
Coupling
Damping
Dynamical systems
Dynamics
Electron spin
electronic structure
Exchange
Exchanging
hybrid models
Joining
Landau-Lifshitz-Gilbert equation
Magnetic fields
Mathematical analysis
Mathematical models
Perturbation theory
Physics
Spin dynamics
Wave dispersion
Wave packets
Wave propagation
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Summary:The real-time dynamics of a classical spin in an external magnetic field and local exchange coupled to an extended one-dimensional system of non-interacting conduction electrons is studied numerically. Retardation effects in the coupled electron-spin dynamics are shown to be the source for the relaxation of the spin in the magnetic field. Total energy and spin is conserved in the non-adiabatic process. Approaching the new local ground state is therefore accompanied by the emission of dispersive wave packets of excitations carrying energy and spin and propagating through the lattice with Fermi velocity. While the spin dynamics in the regime of strong exchange coupling J is rather complex and governed by an emergent new time scale, the motion of the spin for weak J is regular and qualitatively well described by the Landau-Lifschitz-Gilbert (LLG) equation. Quantitatively, however, the full quantum-classical hybrid dynamics differs from the LLG approach. This is understood as a breakdown of weak-coupling perturbation theory in J in the course of time. Furthermore, it is shown that the concept of the Gilbert damping parameter is ill-defined for the case of a one-dimensional system.
ISSN:1367-2630
1367-2630
DOI:10.1088/1367-2630/17/11/113058