A simple madel for the nonretarded dispersive force between an electrically polarizable atom and a magnetically polarizable one

It is known that the consideration or not of retardation effects on the dispersive van der Waals force between two electrically polarizable atoms leads to power laws for the forces that differ only by one power: 1/r(8) for the retarded force and 1/r(7) for the nonretarded one. On the other hand, for the case of an electrically polarizable atom and a magnetically polarizable one, while the retarded force is still proportional to 1/r(8), the nonretarded one is proportional to 1/r(5). Here, employing the fluctuating dipole model for both atoms, we reobtain this quite unexpected behavior for the nonretarded force mentioned above. A physical interpretation is also given for such a result. (C) 2002 American Association of Physics Teachers.