Correlation between magnetism and structural relaxation in thin Fe(001) films patterned by the atomic saw method

We present detailed extended x-ray-absorption fine-structure (EXAFS) studie s carried out on 50-Angstrom epitaxial thin films grown by molecular-beam e pitaxy on MgO(001) substrate prior and after structuration into ribbons by the so-called "atomic saw" method. Because of interfacial strain due to lat tice mismatch (+3.8%), the crystallographic structure of the as-deposited f ilm is demonstrated to be body-centered tetragonal with lattice constants a = 2.915 +/- 0.015 Angstrom and c = 2.82 +/- 0.01 Angstrom. This structure is 2% expanded in plane and - 1.6% compressed along the surface normal as c ompared to the bulk Fe one. After structuration, the patterned 50-Angstrom Fe films show a strong in-plane uniaxial magnetic anisotropy (close to 2.5 kOe). The EXAFS studies provide the clear evidence that the dislocation sli pping process enhances a uniaxial relaxation delta = - 2.5% of the elastic strain field in the Fe him along the direction perpendicular to the ribbons . Through magnetoelastic effects, this relaxation is dearly demonstrated to be at the source of the observed magnetic anisotropy. This paper empha siz es the power of the "phase derivative" method in the analysis of EXAFS spec tra for the determination of crystalline parameters in the case of bcc-type structures.