T. Schrefl , H. Forster, D. Suess, W. Scholz, V. D. Tsiantos and J. Fidler

in Bernhard Kramer (Ed.), Advances in Solid State Physics, Springer Verlag, 2001, p. 623-635

Magnetic switching of small particles, thin film elements and magnetic nanowires becomes increasingly important in magnetic storage and magneto electronic devices. Micromagnetic switching events are studied using a hybrid finite element / boundary element method. The space discretization of the Gilbert equation leads to a system of ordinary differential equations. Its numerical integration provides the time evolution of the magnetization under the influence of an external field. Thermal fluctuations may be treated by a random field. The reversal mode drastically depends on the Gilbert damping constant. Decreasing the damping constant from alpha=1 to alpha<=0.1 changes the reversal mode from uniform rotation to inhomogeneous switching. The decrease of the damping leads to the formation of vortices in circular nanodots and to a nucleation process in columnar grains. Elongated Co particles reverse by rotation if the length of the particle is smaller than 25 nm. Irreversible switching of longer particles occurs due to the formation of a nucleus of reversed magnetization and successive domain wall motion.

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Feb. 13, 2001