  It is well known that for the case of two neutral but electrically
polarizable atoms the consideration or not of retardation effects on the
dispersive van der Waals force between them leads essentially to different
power laws for the forces; while the retarded force is proportional to $1/r^8$,
where $r$ is the distance between the atoms, the non-retarded force is
proportional to $1/r^7$. Here we consider the (repulsive) dispersive force
between an electrically polarizable atom and a magnetically polarizable one and
show that, in contrast to the previous case, a quite unexpected result appears,
namely: while the retarded force is still proportional to $1/r^8$, the
non-retarded force is proportional to $1/r^5$. We employ a semiclassical method
based on the fluctuating dipole model for both atoms.
