Uniaxial magnetic anisotropy of thin epitaxial Fe films nanostructured by the atomic saw method

Abstract

The ‘atomic saw' method, initially developed for semiconductor heterostructures, has been successfully used to cut an iron thin film, epitaxially grown onto a (0 0 1)MgO substrate, into stripes (1 μm–100 nm large and 8–1 nm high) or boxes (whose in-plane dimension ranges from 1 to 3 μm). A structural analysis by atomic force microscopy (AFM) of the created magnetic nanostructures demonstrates the efficiency of this simple method and reveals that their geometries are controlled by the choice of the plastic strain. Magneto-optical study of films cut into stripes exhibit a surprisingly strong uniaxial magnetic anisotropy with the in-plane easy axis perpendicular to the stripes. This strong anisotropy (ranging from 8×105 to 14×105 erg/cm3) can be explained by a uniaxial relaxation of the elastic strain field. Magnetic studies on boxes reveal that the cubic magnetocrystalline energy is recovered since, in this case, the ‘atomic saw' method acts in a biaxial way in the layer plane. Magnetization reversal, contrary to the case of a continuous epitaxial Fe film characterized by rapid displacement of 180 and 90 domain walls, is now governed by nucleation process.