  Focussing on preplanetary grains growth, we discuss the properties of dust
aggregation driven by magnetic dipole forces. While there is no direct evidence
for the existence of magnetic grains present in the solar nebula, there are
reasons to assume they may have been present. We derive analytical expressions
for the cross-section of two interacting dipoles. The effective cross section
depends upon the strength of the magnetic dipoles and the initial velocities.
For typical conditions the magnetic cross section is between 2 and 3 orders of
magnitude larger than the geometric cross section. We study the growth dynamics
of magnetic grains and find that the mass of the aggregates should increase
with time like t^3.2 whereas Brownian motion growth behaves like t^2. A
numerical tool is introduced which can be used to model dust aggregation in
great detail, including the treatment of contact forces, aggregate
restructuring processes and long-range forces. This tool is used to simulate
collisions between magnetic grains or clusters and to validate the analytical
cross-sections. The numerically derived cross section is in excellent agreement
with the analytical expression. The numerical tool is also used to demonstrate
that structural changes in the aggregates during collisions can be significant.
