Mitsuru Ohtake

Preparation of Co(0001)hcp and (111)fcc Films on Single-Crystal Oxide Substrates

Co thin film were prepared on oxide single-crystal substrates of Al2O3(0001)D51, MgO(111)B1, and SrTiO3(111)E21 by ultra high vacuum molecular beam epitaxy. Effects of substrate material and substrate temperate on the film growth and the crystallographic properties were investigated. Co epitaxial thin films of hcp(0001) and/or fcc(111) orientations are obtained on all the substrate. With increasing the substrate temperature, the volume ratio of hcp to fcc increases for the Co films grown on Al2O3 and MgO substrates, whereas the ratio decrease for the Co film grown on SrTiO3 substrate. The in-plane lattice strain is larger than the out-of-plane strain due to accommodation of lattice mismatch between the film and the substrate

Microstructure of hcp-Ni(11̄00)/bcc-Cr(211) Bi-layer Film Grown on MgO(110) Substrate

A Ni epitaxial film with hcp(1100) single-crystal structure is obtained on a Cr(211) underlayer hetero-epitaxially grown on an MgO(110) single-crystal substrate in an early stage of film growth by ultra high vacuum rf magnetron sputtering. Reflection high energy electron diffraction (RHEED) observation indicates that the metastable hcp-Ni crystal tends to transform into more stable fcc crystal with increasing the film thickness. The crystallographic orientation relationship between the hcp and the fcc crystals is determined by RHEED and - scan X-ray diffraction. High-resolution transmission electron microscopy shows that the hcp and the fcc crystals exist separately on the Cr underlayer. The lattice constants of hcp-Ni crystal are determined from X-ray diffraction analysis as a=0.249 nm, c=0.415 nm, and c/a=1.67.

Switching Field and Resolution of MFM Tips Prepared by Coating Fe/Co50Pt50 Magnetic Films

Magnetic force microscope (MFM) tips are prepared by coating Fe(10 nm)/Co50Pt50(x nm)/Ru(5 nm) (at. %) films at 300 °C on Si-base tips of 4 nm radius. The thickness of CoPt layer, x, is varied in a range of 10 – 200 nm. The effects of coating thickness on spatial resolution and switching field of MFM tip are investigated. With increasing the thickness, the resolution deteriorates from 9.4 to 12.1 nm. The switching field increases from 0.675 to 2.025 kOe with increasing the coating thickness from 10 to 200 nm. A tip prepared by coating 100 nm thick Co50Pt50 film which has high resolution and high switching field property is successfully applied to the observation of magnetization structure of high-K u magnetic thin film with L10-ordered structure.