Metastable Ordered Phase Formation in CoPt and Co_3Pt Alloy Thin Films Epitaxially Grown on Single-Crystal Substrates

摘要

CoPt and Co_3Pt alloy thin films are prepared on MgO(111), SrTiO_3(111), and Al_2O_3(0001) single-crystal substrates by varying the substrate temperature in a range from room temperature to 600℃ by using an ultra-high vacuum radio-frequency magnetron sputtering system. The formation of metastable ordered phase and the structural thermal stability are briefly investigated. CoPt and Co_3Pt films with the close-packed plane parallel to the substrate surface grow epitaxially on these oxide single-crystal substrates. CoPt epitaxial films are also formed by employing Pt, Pd, Cu, Cr, Ti, and Ru underlayers hetero-epitaxially grown on MgO(111) substrates. The crystal structure is evaluated by considering the order degree and the atomic stacking sequence of close-packed plane. Metastable ordered phases of L1_1, B_h and D0_(19) are preferentially formed in the CoPt and the Co_3Pt films deposited around 300℃. Metastable ordered phase formation is influenced by the substrate temperature, the film composition, and the underlayer material. With increasing the substrate temperature up to around 300℃, the order degree increases. As the substrate temperature further increases, the order degree decreases. Annealing a disordered film at 300℃ does not effectively enhance ordering. The CoPt and the Co_3Pt films which include metastable ordered phases have flat surfaces and show strong perpendicular magnetic anisotropies reflecting the magnetocrystalline anisotropies of ordered crystals.