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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Feb. 13, 2001