We solved the Landau-Lifshitz equations numerically to examine the time development
of a system of magnetic particles. Constant or periodical external
magnetic field has been applied.
First, the system has been studied without dissipation. Local energy excitations
(breathers) and chaotic transients have been found. The behaviour of
the system and the final configurations can strongly depend on the initial conditions,
and the strength of the external field at an earlier time. We observed some
sudden switching between two remarkably different states. Series of bifurcations
have been found.
When a weak Gilbert-damping has been taken into account, interesting behaviour
has been found even in the case of one particle as well: bifurcation series
and period multiplication leading to chaos. For a system of antiferromagnetically
coupled particles, highly nontrivial hysteresis loops have been produced. The
dynamics of the magnetization reversal has been investigated and the characteristic
time-scale of the reversal has been estimated. For more particles, the energy
spectrum and the magnetization of the system exhibits fractal characteristics for
increasing system size.
Finally, energy have been pumped into the system in addition to the dissipation.
For constant field, complicated phase diagrams have been produced. For
microwave field, it has been found that the chaotic behaviour crucially depends
on the parity of the number of the particles.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.