Anisotropic magnetization of epitaxial Ni nanogroove-arrays prepared by reduction of self-organized oxides

A straight and periodic nanogroove-array pattern was formed on the surface of epitaxial Ni (1 1 1) thin films via a unique process, which included self-organization and reduction of oxides. In the formation of the Ni nanopattern, the epitaxial NiO (1 1 1) thin film grown on an α-Al2O3 (0 0 0 1) substrate by laser molecular-beam epitaxy (LaserMBE) was used as a starting material. The NiO (1 1 1) films were subsequently subjected to thermal treatment at 700 °C in air for the formation of self-organized nanopatterns, and then at 500 °C in a hydrogen atmosphere for reducing NiO to Ni. The epitaxy and morphology of the Ni (1 1 1) nanogroove array were proved by exsitu X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Anisotropic magnetization behavior of the Ni (1 1 1) nanogroove-array pattern was examined by a M–H measurement using a superconducting quantum interference device (SQUID) magnetometer. The M–H squareness ratios for the directions parallel and perpendicular to the nanogrooves were about 0.83 and 0.52, respectively. The coercivity along the parallel line was ∼0.5 kOe, which was approximately 200% of the value for the other direction. From the magnetization results, the parallel direction was considered as the magnetic easy axis in the in-plane orientation, probably due to the shape effect.