  Zero-point energy of surface plasmon modes of mesoscopic metal samples in an
external magnetic field has been considered. The magnetic response of plasmon
vacuum has shown to be diamagnetic. In thin films this surface vacuum
diamagnetism is at least of the same order of magnitude as the magnetism of the
bulk electrons. Thus, a novel type of magnetism shown by thin metallic samples,
which is complementary to the well known Pauli paramagnetic and Landau
diamagnetic contributions to the magnetism of the electron gas has been
demonstrated.
