Surface EXAFS study of metastable magnetic thin films

Epitaxial thin films provide new opportunities to explore the relationship between structure and magnetism. The bidimensionnal character of magnetic f ilms deposited on single-crystal substrates and the occurrence of singular crystallographic structures often confer on these systems electronic and ma gnetic properties that cannot be found in the bulk solids. Although shape a nisotropy would favour an in-plane easy axis of magnetization for thin film s, Ni layers deposited on Cu(001) present a perpendicular magnetic anisotro py in a very wide thickness range. It is shown that this can be explained b y a distorted structure of Ni, originating from the strain induced by the e pitaxy on the Cu substrate. In the field of low-dimensional magnetism, nano structures with a reduced lateral dimension are now being widely investigat ed in view of their technological applications. Thin Fe layers on MgO(001) can be cut into strips by the 'atomic saw' method: a compression of the sub strate induces a dislocation slipping which 'saws' both the substrate and t he Fe film into regular and separated ribbons. The observed magnetic anisot ropy, with the easy axis perpendicular to the strips, is explained by a str uctural relaxation occurring during the structuration process. In these two studies, a precise structural characterization and simple magnetoelastic m odels allow the magnetic behaviour of the systems to be described. The stru cture of the films can be described as an elastic deformation of the bulk s tructure.