ordered FePd alloy epitaxial thin films are prepared on MgO substrates of (001), (110), and (111) orientations by two different methods; by direct deposition at high temperature of 600 C and by preparation of film at a low temperature of 200 C followed by high temperature annealing at 600 C. The influence of preparation method on film structure, order degree, surface roughness, and magnetic property are investigated. Films with ordered structure grow epitaxially on MgO substrates when deposited at 600 C. Epitaxial films with disordered structure prepared at 200 C transform into ordered structure by annealing at 600 C. Although order degree is similar between two kinds of FePd film prepared by different methods, the surface roughness and coercivity are different. The films prepared by annealing have very flat continuous surfaces as well as lower coercivities which results from easy movement of domain walls. The two step process employing low temperature film deposition followed by high temperature annealing is very effective in the preparation of ordered alloy films with very flat surfaces, which are important for practical device applications.Index Terms-Annealing, FePd alloy thin film, phase transformation from to , surface roughness.

Abstract. FePd, FePt, and CoPt alloy thin films are prepared on MgO(001) single-crystal substrates by employing a two-step method consisting of sputter deposition at low-temperature (room temperature) followed by high-temperature annealing at 600 °C. FePd, FePt, and CoPt single-crystal films with disordered structure (A1) grow epitaxially on MgO substrates at room temperature. By annealing these disordered films at 600 °C, a transformation from A1 to L1 0 -ordered phase occurs. The order degrees of annealed FePd, FePt, and CoPt films are 0.63, 0.38, and 0.16, respectively. The films before annealing have very flat surfaces and the flat surfaces are kept after annealing. The arithmetical mean surface roughness values of annealed FePd, FePt, and CoPt films are 0.3, 0.1, and 0.2 nm, respectively. The two-step method is considered to be useful for preparation of FePd, FePt, and CoPt alloy thin films with flat surfaces, which are necessary for practical applications.

An FePt alloy thin film with L10 structure formed on a (001)-oriented polycrystalline underlayer or on a (001)-oriented single-crystal substrate may involve (100) variant with the c-axis lying in the film plane in addition to (001) variant with the c-axis normal to the substrate surface. In the present study, FePt(2-40 nm) films with and without MgO(2 nm) cap layers are prepared on MgO(001) single-crystal substrates by employing a two-step formation method consisting of low-temperature deposition followed by high-temperature annealing. Disordered FePt(001) single-crystal films with and without MgO(001) single-crystal cap layers epitaxially grow on the substrates at 200 °C. For the films thinner than 10 nm, the in-plane and out-of-plane lattices are respectively expanded and shrunk due to accommodation of the lattice misfit of film with respect to the substrate. With increasing the thickness up to 40 nm, the strain is relaxed. The phase transformation from A1 to L10 occurs when the films are annealed at 600 °C. The cap layer seems to prevent the strain release and to promote the phase transformation along the perpendicular direction. The c-axis orientation is controlled to be perpendicular by using the two-step method for the FePt films of thicknesses less than 10 nm with MgO cap layers. On the contrary, the film of 40 nm thickness with cap layer and the films of 2-40 nm thicknesses without cap layers involve small volumes of L10(100) variant. The order degrees of films with cap layers are higher than those of films without cap layers. The films with cap layers have flat surfaces with the arithmetical mean roughness values lower than 0.3 nm for all the investigated thicknesses, whereas an island-like surface is formed for the 2-nm-thick film without cap layer. The film consisting of only L10(001) variant shows a strong perpendicular magnetic anisotropy and a very low in-plane coercivity. Introduction of MgO cap layer is useful in aligning the c-axis perpendicular to the substrate surface, enhancing the L10 ordering, forming a flat surface, and achieving a strong perpendicular magnetic anisotropy.

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FePd alloy films of 1 to 500 nm thicknesses are prepared on MgO(001) single-crystal substrates by employing a two-step method consisting of low-temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. The influences of film thickness on the crystallographic orientation, the degree of L1 0 ordering, the magnetic property, and the surface roughness are systematically investigated. FePd(001) single-crystal films with disordered structure grow epitaxially on the substrates at 200 °C. The in-plane lattice is expanded to accommodate the lattice misfit between film and substrate (-9%). The distortion is decreased with increasing the thickness. When the films are annealed at 600 °C, transformation to L1 0 phase occurs. The films thinner than 40 nm consist of L1 0 (001) variant with the c-axis normal to the substrate surface, where the transformation along the perpendicular direction is preferentially taking place. On the contrary, the films thicker than 100 nm involve L1 0 (100) and L1 0 (010) variants whose c-axes are lying in the film plane and rotated around the film normal by 90° each other. The volume ratio of L1 0 (001) variant decreases to 0.22, as the thickness increases up to 500 nm. The order degrees of films thinner than 40 nm are 0.6-0.7. With further increasing the thickness, the order degree decreases. The lattice deformation in disordered FePd film before annealing is effective in enhancing L1 0 ordering and aligning the c-axis perpendicular to the substrate surface. The easy magnetization direction varies from perpendicular to in-plane, as the thickness increases from 100 to 500 nm. The magnetic anisotropy is affected by the crystal orientation and the order degree. The films thinner than 2 nm have island-like surfaces, where condensation of deposited atoms on substrate is taking place during the annealing process. When the thickness is increased beyond 10 nm, flat surface is kept before and after annealing.Index Terms-c-axis orientation, FePd alloy single-crystal film, L1 0 structure, order degree, surface morphology.