Langevin Dynamics of Small Ferromagnetic Particles and Wires

W. Scholz, J. Fidler, D. Süss, and T. Schrefl

Proceedings of 16th IMACS World Congress on Scientific Computation, Applied Mathematics and Simulation, Aug. 2000, Lausanne, Switzerland. (2000) in press.

Thermally induced magnetization reversal of small particles is studied using Langevin dynamics. The deterministic Gilbert equation of motion transforms to a stochastic partial differential equation adding a random thermal field to the effective field. The space discretization leads to a system of stochastic differential equations with multiplicative noise which is interpreted in the sense of Stratonovich and solved using the method of Heun. The ellipsoids and wires reverse by rotation if the length of the particle is l<=16 nm. In longer wires, a nucleus of reverse magnetization forms at one end of the particle. The activation volumes associated with the different reversal modes are calculated from the field dependence of the energy barrier. The calculated activation volume is v=(2.1 nm)3 for Co-wires with l>20 nm.

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Oct. 18, 2001