| This thesis describes several projects related to simulation of the dynamics of magnetic systems. Part one is methodological, part two is theoretical, parts three and four are applications to specific systems, namely, thin film and nanoparticles. In chapter 2, a quaternion algorithm is described for micromagnetic simulation. Its major advantage is that it separates precessional and dissipational rotations in the Landau-Lifshitz (LL) equation, which allows the former to be computed analytically over long time intervals. This means a longer time increment Deltat can be used than in the conventional algorithms, especially for problems with low anisotropy and weak exchange coupling. The linear stability properties of the quaternion method are also examined in comparison with the Euler's method. The quaternion method is found to be significantly more stable.;Micromagnetic calculation results based on the LL equation have been observed to depend strongly on the cell size. We took a coarse-graining approach to the cell size dependence: we simulate using cell size L, study the dynamics of a cell of size 2L, and determine an effective damping coefficient on the larger scale. In principle, this makes it possible to coarse grain from the atomic scale to determine the macroscopic micromagnetic damping coefficient.;Simulations of pulse-induced magnetization-rotation experiments in Permalloy are presented. These lead to temporary domain formation ("thermal ripple") and help to explain the time dependence of experimental results. To understand and visualize the motion, it is very useful to exploit a mathematical isomorphism of this problem to a particle on a circular track ("roller coaster"). The height of this track is proportional to the Stoner-Wohlfarth energy. The roller coaster analogy is more intuitive than the conventional "M precesses about the effective field" picture.;A simple method for parameterizing the sweep-rate dependence of the coercivity is studied. It is used to fit data from LL dynamic simulation, to extrapolate to experimental time scales. It is a generalization of the Sharrock theory in which all the data fall on a single universal curve if the coercivity and sweep-rate are scaled properly. |
