  Ferromagnetism was observed in a Pt(100) ultrathin film deposited on a
SrTiO3(100) substrate. The ferromagnetism, which appears in films with
thicknesses of 2.2-4.4 nm, periodically changes with a period of approximately
1 nm (5-6 monolayers) depending on the film thickness. This is consistent with
the period derived from the quantum-well states formed in the thin film. X-ray
magnetic circular dichroism measurements show the evidence of appearance of
intrinsic ferromagnetism in Pt(100) ultra-thin film. In addition, present
results suggest a possibility that the orbital magnetic moment of pure Pt is
much smaller than that of the Pt/ferromagnetic multilayer system. These results
will provide a potential new mechanism for origin of the large magnetic
anisotropy in Pt components.
