Surface extended x-ray absorption fine structure studies of metastable magnetic thin films and nanostructures

Magnetic films deposited on single-crystal substrates have been the subject of numerous studies since their bi-dimensional or nanostructured character provides important extensions of the family of bulk magnetic solids. For these objects, the knowledge of their size, shape and structure at the atomic scale are mandatory for an understanding of their unusual magnetic properties. After a short introduction to the strengths of extended x-ray absorption fine structure (EXAFS) for local structure determination, we will concentrate on three well defined cases. Thin Ni layers deposited on Cu(001) present a perpendicular magnetic anisotropy in a very wide thickness range, and thin Fe layers on MgO(001) cut into stripes by the 'atomic saw' (AS) method have a magnetization easy axis oriented perpendicular to the stripes. In both cases, a precise structural characterization obtained by EXAFS and simple magneto-elastic models allow description of their magnetic behaviour. The growth of a cobalt film on a vicinal Cu(11n) surface induces a uniaxial magnetic anisotropy. Although the steps are clearly at the origin of this behaviour, the exact mechanism (lower coordination at step edges, anisotropic strain) remains obscure. Detailed studies of the morphology by STM and of the structure by EXAFS allow the conclusion that the step-induced magnetic anisotropy does not originate from an in-plane anisotropic structural relaxation but is more likely related to the stepped film morphology.