2015 年 39 巻 1 号 p. 15-20
CoPt and Co3Pt alloy epitaxial films with the close-packed plane parallel to the surface are prepared on MgO(111) single-crystal substrates heated at 300 °C by varying the film thickness in a range between 2 and 40 nm. The structure is investigated from the viewpoints of the order degree and the atomic stacking sequence of close-packed plane. Metastable ordered phase formation is recognized for both CoPt and Co3Pt films. The CoPt and the Co3Pt films involve L11 and Bh(+D019) phases, respectively. Higher order degrees are recognized for thicker CoPt and Co3Pt films. As the thickness increases, the strain caused by accommodation of the lattice mismatch between film and substrate decreases. The ratios of out-of-plane to in-plane lattice spacings, 2dL11(222) / 2dL11(440) and 2dBh(+D019)(0002) / 2dBh(+D019)(2240), of CoPt and Co3Pt films, respectively, decrease from 1.638 to 1.630 and from 1.637 to 1.616 with increasing the thickness from 2 to 40 nm. The films involving metastable phases show strong perpendicular magnetic anisotropies reflecting the magnetocrystalline anisotropies of L11 and Bh(+D019) crystals.