S. Komineas and N. Papanicolaou
Department of Physics, University of Crete,
P.O. Box 2208, GR--710.03 Heraclion, Crete, Greece
and Research center of Crete.
Abstract
A direct link between the topological complexity of ferromagnetic
media and their dynamics has recently been established through the
construction of unambiguous conservation laws as moments of a topological
vorticity. In the present paper we carry out this program under completely
realistic conditions, with due account of the long-range magnetostatic
field and related boundary effects. In particular, we derive unambiguous
expressions for the linear and angular momentum in a ferromagnetic film
which are then used to study the dynamics of magnetic bubbles under the
influence of an applied magnetic-field gradient. The semi-empirical golden
rule of bubble dynamics is verified in its gross features but not in its finer
details. A byproduct of our analysis is a set of virial theorems generalizing
Derrick's scaling relation as well as a detailed recalculation of the
fundamental magnetic bubble.