# Regensburg 2002 – wissenschaftliches Programm

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# MA: Magnetismus

## MA 17: Exchange Coupling

### MA 17.5: Vortrag

### Donnerstag, 14. März 2002, 16:15–16:30, H22

**Long-range magnetic interactions due to the Casimir effect** — •Patrick Bruno — Max-Planck-Institut für Mikrostruturphysik, Weinberg 2, O6120 Halle, Germany

One usually considers that there exists essentially two kinds of magnetic interactions between magnetic moments or magnetized bodies: (i) the magnetostatic dipole-dipole interaction, and (ii) the electron-mediated exchange interaction.

Here, I point
out that there exists a further (so far overlooked) mechanism
of magnetic interaction, which results from the zero-point
quantum fluctuations of the electromagnetic field (Casimir
effect). The Casimir magnetic interaction between magnetic
metallic layers
separated by vacuum (or by a dielectric) has been
calculated in the limit of large interlayer distance *D* and is
found to decay as *D*^{−4}.

In view of the fact that the interlayer exchange interaction
decreases
exponentially with *D* for a dielectric spacer
and that the interlayer magnetostatic interaction
is essentially zero when the layers are
homogenously magnetized, the new Casimir magnetic interaction
(although very small) is therefore the dominant magnetic
interlayer
interaction for
sufficiently large distances, due to its long-range character.
The detection of
this new fundamental effect sets a new challenge in experimental
magnetism.