Remagnetization processes in ferrofluids: numerical simulations using the Langevin dynamics

D. V. Berkov - N. L. Gorn - D. Stock

Innovent Technologieentwicklung e.V., D-07745 Jena, Germany

Abstract
We report an important methodical progress in numerical simulations of fast remagnetization processes in ferrofluids using the stochastic (Langevin) dynamics. The system of Langevin equations we use to describe ferrofluids includes all their relevant degrees of freedom: translational and rotational motion of ferrofluid particles and rotation of the particle magnetic moment with respect to the particle itself. At present the magnetodipolar and steric repulsion interparticle interactions are taken into account (hydrodynamic interactions not included). Due to very different characteristic time scales of the magnetic moment motion ( ∼ 10⁻⁹ − 10⁻¹⁰ s) and mechanical motion of ferrofluid particles ( ∼ 10⁻⁵ − 10⁻⁶ s), a straightforward integration of equations of motion is extremely inefficient. For this reason we have developed a combined Langevin dynamics/Monte Carlo (MC) method, whereby the magnetic subsystem is equilibrated using the MC algorithm for the given positions and orientations of magnetic particles. We present some simulation examples for remagnetization processes, which could be studied with our method, in particular, ferrofluid magnetization relaxation after a sudden change of an external field and remagnetization in an oscillating field. Figs 3, Refs 8.