SURFACE-STRUCTURE AND MORPHOLOGY OF MG-SEGREGATED EPITAXIAL FE3O4(001) THIN-FILMS ON MGO(001)

We have investigated the structural and compositional changes that are induced by the segregation of substrate Mg to the surface of 1 mu m-t hick Fe3O4(001) films on MgO(001). The thin films have been grown with plasma-assisted MBE. Characterization with reflection high-energy ele ctron diffraction, x-ray diffraction, and superconducting quantum inte rference device magnetometry, show slightly strained, single-crystalli ne Fe3O4 films. For the surface studies, we have combined low-energy e lectron diffraction, and scanning .unneling microscopy to study surfac e structure and morphology. The initial surface content was determined by x-ray photoelectron spectroscopy. The surfaces of the molecular-be am epitaxy-grown samples are flat and show a (root 2 x root 2)R45 degr ees reconstruction with respect to the Fe3O4 surface unit cell. Onset of Mg segregation to the surface occurs around 670 K, with long, narro w extensions of terraces growing along the [110] and <[1(1)over bar 0] > directions. Heating in an oxygen atmosphere induces a 1x4 surface re construction, and extremely long (approximate to 1000 Angstrom), wide terraces. We attribute this annealing stage to the formation of a MgFe 2O4 surface phase, exhibiting highly anisotropic surface diffusion and step formation energy.