AVS 49th International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeA

Paper MI-WeA7
A New Equation for Magnetization Dynamics Based Upon Transverse Relaxation Processes

Wednesday, November 6, 2002, 4:00 pm, Room C-205

Session: Magnetization Dynamics
Presenter: T.J. Silva, National Institute for Standards and Technology
Authors: T.J. Silva, National Institute for Standards and Technology
R. Lopusnik, National Institute for Standards and Technology
J.P. Nibarger, National Institute for Standards and Technology
T. Gerrits, University of Nijmegen, The Netherlands
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We present a new equation for magnetodynamic response, derived from the Bloch-Bloembergen formulation for spin relaxation phenomena. The new equation is vectorial and adapted for all possible field geometries. The longitudinal and transverse relaxation rates are constrained to insure conservation of the magnetization. As such, the new equation is amenable to finite-element micromagnetic simulations. Subject to the constraint of constant magnetization, the longitudinal relaxation rate cannot be constant during free induction decay in unbiased ferromagnetic films. However, if the transverse relaxation rate is held constant, the resulting equation is of the Landau-Lifshitz form but with an additional dependence of the damping term on longitudinal field. The field dependence strongly renormalizes the relaxation times for thin films in small bias fields such that MHz transverse relaxation rates for undressed excitations can result in nanosecond damping times in a thin film geometry. Such strong renormalization allows for a significant contribution by weak spin-orbit effects to the overall damping of precessional excitations in thin film structures. Inverse field dependence for the damping parameter in thin films is predicted by the new equation, in agreement with recent data obtained by inductive and optical methods.@footnote 1@ In addition, highly viscous response is predicted when the magnetization is subject to large magnetic field pulses along the hard axis of uniaxial anisotropy films, also in agreement with recent observations of metastable states in homogeneous Permalloy films.@footnote 2@ Implications for device performance and data storage applications will be discussed. @FootnoteText@ @footnote 1@ T. J. Silva, T. M. Crawford, IEEE Trans. Magn. 35, 671 (1999). @footnote2@ P. Kabos, S. Kaka, S. E. Russek, T. J. Silva, IEEE Trans. Magn. 36, 3050 (2001).