We present magneto-optic Kerr effect, x-ray photoelectron spectroscopy, and x-ray magnetic circular dichroism data from epitaxial thin ferromagnetic film grown onto GaAs(001)-(4x6). By seeding a half monolayer of Co in an Fe double wedge with a total thickness of six monolayers, we introduced a magnetic marker, which, similarly to Mossbauer spectroscopy, allows us to probe the magnetic and chemical properties across the ferromagnetic film in a layer-dependent analysis. The long-range magnetization is found to persist within the Fe overlayer at any depth, until a reduction is observed at the interface with GaAs. Correspondingly the spin magnetic moment is maximum at the center of the film and is reduced both at the interface and at the surface. We found also an enhancement of the orbital magnetic moment and orbit-to-spin magnetic-moment ratio near the interface with the GaAs substrate. Further, an uneven segregation (diffusion) between Ga and As has been found, and its influence on magnetic properties is discussed.