$L1_{0}$ Ordered FePd, FePt, and CoPt Thin Films With Flat Surfaces Prepared on MgO(110) Single-Crystal Substrates

FePd, FePt, and CoPt alloy thin films are prepared on MgO(110) single-crystal substrates by using two different methods. One is one-step method consisting of deposition at an elevated substrate temperature of 600°C and the other is two-step method consisting of low-temperature deposition at 200°C followed by annealing at 600°C. The crystal structure, the crystallographic orientation, and the surface morphology are compared. L1₀ ordered FePd, FePt, and CoPt films epitaxially grow on the substrates with three variants, (110), (101), and (011), when deposited at 600°C. The c-axis of L1₀(110) variant is lying in the film plane, whereas those of L1₀(101) and L1₀(011) variants are 45° canted from the substrate surface. Disordered FePd, FePt, and CoPt single-crystal films of (110) orientation are formed by deposition at 200°C. An A1-L1₀ phase transformation occurs along A1[001], A1[010], and A1[001] by annealing the disordered films at 600°C. The annealed films thus consist of three L1₀ variants. Similar final crystal structure and orientation are realized in the FePd, the FePt, and the CoPt films prepared by employing the two different methods. The L1₀ ordered films prepared by one-step method have island-like surfaces involving facets, whereas those prepared by two-step method have very flat surfaces with the arithmetical mean roughness lower than 0.3 nm. The two-step method is useful for preparation of L1₀ ordered films with flat surfaces.