Magnetic properties, morphology and interfaces of (Fe/Si)n nanostructures

A systematic study of the iron¿silicon interfaces formed upon preparation of (Fe/Si) multilayers has been performed by the combination of modern and powerful techniques. Samples were prepared by molecular beam epitaxy under ultrahigh vacuum onto Si wafers or single crystalline Ag(100) buffer layers grown on GaAs(100). The morphology of these films and their interfaces was studied by a combination of scanning transmission electron microscopy, X-ray reflectivity, angle resolved X-ray photoelectron spectroscopy and hard X-ray photoelectron spectroscopy. The Si-on-Fe interface thickness and roughness were determined to be 1.4(1) nm and 0.6(1) nm, respectively. Moreover, determination of the stable phases formed at both Fe-on-Si and Si-on-Fe interfaces was performed using conversion electron Mössbauer spectroscopy on multilayers with well separated Si-on-Fe and Fe-on-Si interfaces. It is shown that while a fraction of Fe remains as α-Fe, the rest has reacted with Si, forming the paramagnetic FeSi phase and a ferromagnetic Fe rich silicide. We conclude that there is an identical paramagnetic c-Fe1-xSi silicide sublayer in both Si-on-Fe and Fe-on-Si interfaces, whereas an asymmetry is revealed in the composition of the ferromagnetic silicide sublayer.The financial support of the Spanish MINECOMAT2011-23791 and MAT2015-53921-R, Aragonese DGA-IMANAE34 (cofounded by Fondo Social Europeo) and European FEDER funds is acknowledged. Program of the President of the Russian Federation for the support of leading scientific schools (Scientific School 2886.2014.2), RFBR (Grant no. 13-02-01265), the Ministry of Education and Science of the Russian Federation (State contract no. 02.G25.31.0043 and State task no. 16.663.2014К)Peer Reviewe