In the introduction we have mentioned that the Rosensweig instability is at
a first glance counterintuitively.
That is, because the newly deformed surface
has an increased surface and hydrostatic energy compared with a plane surface.
Obviously the increase is caused by the costs of energy to lift up the fluid against
gravitation and to create more surface area.
Therefore gravitation and surface
tension stabilize the plane surface.
The destabilization of the flat reference state
is caused by the magnetic field because it favors a deformed surface profile, as
sketched in the following.
Let us look at the sinusoidal surface deformation in
Fig. 3, which is symmetric with respect to the even surface, denoted by a dashed
line. In a crest the field lines stay a prolonged distance within the MF which
results in a decline of the magnetic energy due to the increased magnetization