Osamu Yabuhara

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

Preparation and characterization of Co single-crystal thin films with hcp, fcc and bcc structures

Co crystals with three different structures are realized in the form of single-crystalthin films hetero-epitaxially grown on single-crystal substrates by ultrahigh vacuum rf magnetron sputtering. hcp-, fcc-, and bcc-Co single-crystalfilms are formed on Cr(211)bcc, Cu(100)fcc, and GaAs(110) B3, respectively. The film growth process is studied by RHEED, and the lattice constants of these Co films are determined by x-ray diffraction. The magnetization properties of these thin films are reflecting the magnetocrystalline anisotropies of Co crystals with the easy magnetization axes along hcp〈0001〉, fcc〈111〉, and bcc〈100〉 directions.

Structure and magnetic properties of FePd-alloy epitaxial thin films grown on MgO single-crystal substrates with different orientations

FePd-alloy epitaxialfilms were prepared on MgO substrates of (100) B 1, (110) B 1, and (111) B 1 orientations at a temperature of 600 °C by ultrahigh vacuum rf magnetron sputtering. The structural and the magnetic properties vary depending on the substrate orientation. L10–FePd(001) films are obtained on MgO(100) B 1 substrates, whereas L10–FePd(101) films with the c-axis canted from the perpendicular direction are epitaxially grown on MgO(111) B 1 substrates with six variants. FePd epitaxialfilms consisting of L10(100) and L10(112) crystals are formed on MgO(110) B 1 substrates. A higher long range ordering parameter is obtained on the order of FePd/MgO(100) B 1 > (110) B 1 > (111) B 1. The filmsgrown on MgO(100) B 1 substrates show perpendicular magnetic anisotropy, whereas the filmsgrown on MgO(110) B 1 and MgO(111) B 1 substrates are easily magnetized in in-plane directions. The magnetization properties reflect the magnetocrystalline anisotropies of bulk L10–FePd crystal.

Formation of SmFe5(0001) ordered alloy thin films on Cu(111) single-crystal underlayers

SmFe5(0001) single-crystal thin films are prepared by molecular beam epitaxy employing Cu(111) single-crystal underlayers on MgO(111) substrates. The Cu atoms diffuse into the Sm-Fe layer and substitute the Fe sites in SmFe5 structure forming an alloy compound of Sm(Fe,Cu)5. The Sm(Fe,Cu)5 film is more Cu enriched with increasing the substrate temperature. The Cu underlayer plays an important role in assisting the formation of the ordered phase.

Preparation and characterization of Co epitaxial thin films on Al2O3(0001) single-crystal substrates

Co epitaxial thin films were prepared on Al2O3(0001) single-crystal substrates in a substrate temperature range between 50 and 500 °C by ultra high vacuum molecular beam epitaxy. Effects of substrate temperature on the structure and the magnetic properties of the films were investigated. The films grown at temperatures lower than 150 °C consist of fcc- Co(111) crystal. With increasing the substrate temperature, hcp-Co(0001) crystal coexists with the fcc crystal and the volume ratio of hcp to fcc crystal increases. The films prepared at temperatures higher than 250 °C consist primarily of hcp crystal. The film growth seems to follow island-growth mode. The films consisting primarily of hcp crystal show perpendicular magnetic anisotropy. The domain structure and the magnetization properties are influenced by the magnetocrystalline anisotropy and the shape anisotropy caused by the film surface roughness.

Microstructure and Magnetic Properties of bcc-Co Films Epitaxially Grown on GaAs(110)B3 Single-Crystal Substrates

bcc-Co(110) single-crystal films were obtained on GaAs(110)B3 substrates by ultrahigh-vacuum rf magnetron sputtering. The detailed film structures are studied by refection high energy electron diffraction, X-ray diffraction, and transmission electron microscopy. The lattice constants of bcc-Co film are determined to be (a, b, c, c/a) = (0.2789 nm, 0.2789 nm, 0.2825 nm, 1.013). The in-plane lattice spacing is 2.6% larger than the out-of-plane lattice spacing due to accommodation of lattice mismatch. The magnetization properties of bcc-Co film reflect the magnetocrystalline anisotropy of bcc-Co crystal with the easy magnetization axes along bcc directions.

Preparation of SmNi5 and Sm(Ni,T)5[T=Co,Fe] ordered alloy thin films on Cu(111) underlayers

SmNi 5 and Sm ( Ni , T ) 5 [ T = Co , Fe ] epitaxialthin films with the c -axis perpendicular to the substrate surface are successfully prepared on Cu underlayers heteroepitaxially grown on MgO(111) single-crystal substrates. The nucleation behavior of SmNi 5 and Sm ( Ni , T ) 5 crystals on Cu(111) underlayers were investigated. The SmNi 5 and the Sm ( Ni , Co ) 5 films consist of two types of domains whose orientations are rotated around the film normal by 30° each other, whereas the Sm ( Ni , Fe ) 5 film is a single crystal. The nucleation and the domain volume ratio seem to be controllable by adjusting the kind and the composition of transition metal elements.