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Co crystals with three different structures are realized in the form of single-crystal thin films hetero-epitaxially grown on single-crystal substrates by ultrahigh vacuum rf magnetron sputtering. hcp-, fcc-, and bcc-Co single-crystal films 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.

Metastable hcp-Ni and hcp-NiFe epitaxial thin films are prepared on Au(100) fcc single-crystal underlayers by molecular beam epitaxy. The epitaxial growth and the transformation from metastable hcp to more stable fcc phase are studied by in-situ reflection high-energy electron diffraction. In an early stage of film growth, hcp(11 20) crystal is stabilized through hetero-epitaxial growth. The epitaxial orientation relationship between the film and the underlayer is determined to be hcp (11 20)[0001], hcp(11 20)[1 100] k Au (100)[001] fcc . With increasing the film thickness, the hcp structure starts to transform into fcc structure. High-resolution transmission electron microscopy shows that the film consists of a mixture of hcp and fcc crystals and that a large number of stacking faults exist parallel to the close-packed plane. The results suggest that the hcp structure starts to transform from these stacking faults into fcc structure in the lateral direction by atomic displacement parallel to the hcp(0001) close-packed plane. The crystallographic orientation relationships between the hcp and transformed fcc crystals are determined to be fcc (110)[1 1 1], fcc(110)[1 11] k hcp(11 20)[0001] and fcc(110)[ 11 2], fcc(110)[1 1 2] k hcp(11 20)[1 100].

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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<100> directions.