Magnetization dynamics in nanoparticle systems:: Numerical simulation using Langevin dynamics

We report on recent progress achieved by the development of numerical methods based on the stochastic (Langevin) dynamics applied to systems of interacting magnetic nanoparticles. The method enables direct simulations of the trajectories of magnetic moments taking into account (i) all relevant interactions, (ii) precession dynamics, and (iii) temperature fluctuations included via the random (thermal) field. We present several novel results obtained using new methods developed for the solution of the Langevin equations. In particular, we have investigated magnetic nanodots and disordered granular systems of single-domain magnetic particles. For the first case we have calculated the spectrum and the spatial distribution of spin excitations. For the second system the complex ac susceptibility chi(omega, T) for various particle concentrations and particle anisotropies were computed and compared with numerous experimental results.