Modulated magnetic structures in chemically homogeneous films

Summary form only given. Increasing storage density requirements in information technology have continued to motivate the exploration of new magnetic media. Several approaches are now being studied intensively, such as stabilizing nanoscale magnetic domains in continuous films and patterning magnetic films into isolated dots. In this work we introduce a new type of magnetic medium where the spin configurations are engineered in chemically homogenous magnetic films. Such a medium not only maintains the surface planarity but also the homogeneity of the magnetic materials. Substrates with laterally modulated single-crystal and polycrystalline surface regions were used to induce selective epitaxial growth of a ferromagnetic Ni film. The samples have a structure of GaAs/Co(1.8 nm)/Cu(70 nm)/Ni(5 nm)/Cu(5 nm). Ultrathin NiO (1 nm) patterns were used to modulate the GaAs substrate surface. The films that interfaced directly with GaAs grow epitaxially and the Ni magnetization is oriented out-of-plane. The films that interfaced with the NiO patterns have polycrystalline structures and the Ni magnetization is directed in the plane. The co-existence of the polycrystalline and epitaxial features are confirmed by in situ reflection high-energy electron diffraction analyses. Atomic force microscopy was used to examine the sample surface yielding statistical roughness parameters in the range similar to that of epitaxial continuous Cu/Ni/Cu films. The co-existence of the in-plane and out-of plane magnetization regions in the films was imaged by magnetic force microscopy, also further confirmed by magneto-optic Kerr effect and superconducting quantum-interference device measurements. The 90 degree transition between the in-plane and out-of-plane regions, which is due to the spatially varying anisotropy properties of the film, corresponds to a new type of magnetic wall (the ´anisotropy constrained magnetic wall´). Micromagnetic simulations show that the spin transition regions is - symmetric, has a small out-of-plane component and has no mobility under external perturbation.