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

Abstract

Magnetic films deposited on single-crystal substrates have been the subject ofnumerous studies since their bi-dimensional or nanostructured character providesimportant extensions of the family of bulk magnetic solids. For these objects, theknowledge of their size, shape and structure at the atomic scale are mandatory foran understanding of their unusual magnetic properties. After a short introductionto the strengths of extended x-ray absorption fine structure (EXAFS) for localstructure determination, we will concentrate on three well defined cases. Thin Nilayers deposited on Cu(001) present a perpendicular magnetic anisotropy in a verywide thickness range, and thin Fe layers on MgO(001) cut into stripes bythe ‘atomic saw’ (AS) method have a magnetization easy axis orientedperpendicular to the stripes. In both cases, a precise structural characterizationobtained by EXAFS and simple magneto-elastic models allow descriptionof their magnetic behaviour. The growth of a cobalt film on a vicinalCu(11n)surface induces a uniaxial magnetic anisotropy. Although the steps are clearly atthe origin of this behaviour, the exact mechanism (lower coordination at stepedges, anisotropic strain) remains obscure. Detailed studies of the morphologyby STM and of the structure by EXAFS allow the conclusion that thestep-induced magnetic anisotropy does not originate from an in-plane anisotropicstructural relaxation but is more likely related to the stepped film morphology.