The correlation between mechanical stress and magnetic anisotropy in ultrathin films

The impact of stress-driven structural transitions and of film strain on th e magnetic properties of nm ferromagnetic films is discussed. The stress-in duced bending of film-substrate composites is analysed to derive informatio n on film stress due to lattice mismatch or due to surface-stress effects. The magneto-elastic coupling in epitaxial films is determined directly from the magnetostrictive bending of the substrate. The combination of stress m easurements with magnetic investigations by the magneto-optical Kerr effect (MOKE) reveals the modification of the magnetic anisotropy by film stress. Stress-strain relations are derived for various epitaxial orientations to facilitate the analysis of the substrate curvature. Biaxial film stress and magnetoelastic coupling coefficients are measured in epitaxial Fe films in situ on W single-crystal substrates. Tremendous film stress of more than 1 0 GPa is measured in pseudomorphic Fe layers, and the important role of fil m stress as a driving force for the formation of misfit distortions and for inducing changes of the growth mode in monolayer thin films is presented. The direct measurement of the magneto-elastic coupling in epitaxial films p roves that the magnitude and sign of the magneto-elastic coupling deviate f rom the respective bulk value. Even a small film strain of order 0.1% is fo und to induce a significant change of the effective magneto-elastic couplin g coefficient. This peculiar behaviour is ascribed to a second-order strain dependence of the ma,magneto-elastic energy density, in contrast to the Li near strain dependence that is valid for bulk samples.