  We investigated the mechanism of the spin-reorientation transition (SRT) in
the Ni/Fe/Ni/W(110) system using in situ low-energy electron microscopy, x-ray
magnetic circular dichroism measurements, and first principles electronic
structure calculations. We discovered that the growth of Fe on a flat Ni film
on a W (110) crystal resulted in the formation of nanosized particles, instead
of a uniform monolayer of Fe as commonly assumed. This interfacial
nanostructure leads to a change of the system's dimensionality from two
dimensional- to three dimensional-like, which simultaneously weakens the
dipolar interaction and enhances the spin-orbit coupling in the system and
drives the observed SRT.
