Structure Analysis of Fe-Co and Fe-Co-B Alloy Thin Films Formed on MgO(001) Substrate

抄録

  Fe-Co and Fe-Co-B alloy films of 40 nm thickness are prepared by sputtering on MgO(001) single-crystal substrates using alloy targets of (Fe_0.7Co_0.3)_100–xB_x (x = 0, 5, 10, 15 at. %) by varying the substrate temperature from room temperature (RT) to 600 °C. The film structure is investigated by reflection high-energy electron diffraction and out-of-plane, in-plane, and pole-figure X-ray diffractions. Preparation condition of epitaxial film is found to depend on the B content and the substrate temperature. Epitaxial (Fe_0.7Co_0.3)_100–xB_x films are obtained at the investigated temperatures for the B contents lower than 5 at. %, whereas films with the B contents of 10 and 15 at. % grow epitaxially at temperatures higher than 400 and 600 °C, respectively. Single-crystal films of bcc(001) orientation are formed at temperatures higher than RT, 200, 400, and 600 °C for the B contents of 0, 5, 10, and 15 at. %, respectively. As the substrate temperature decreases, the epitaxial films with B contents of 5–15 at. % tend to involve four types of bcc(122) variant whose orientations are rotated around the film normal by 90° each other. The (Fe_0.7Co_0.3)₉₀B₁₀ film deposited at RT and the (Fe_0.7Co_0.3)₈₅B₁₅ films deposited at temperatures from RT to 200 °C are found to be consisting of bcc polycrystal and amorphous, respectively. The structure is thus determined to vary in the order of bcc(001) single-crystal => bcc(001) and bcc(122) epitaxial crystals => bcc polycrystal => amorphous with increasing the B content and with decreasing the substrate temperature. The lattices of single-crystal Fe-Co (x = 0 at. %) and Fe-Co-B (x = 5–15 at. %) films are respectively expanded along the in-plane and the perpendicular directions. The single-crystal Fe-Co films show in-plane magnetic anisotropies with the easy magnetization directions of bcc[100] and bcc[010], which is reflecting the magnetocrystalline anisotropy of bulk bcc-Fe₇₀Co₃₀ alloy. On the contrary, the single-crystal Fe-Co-B films show almost isotropic in-plane magnetic properties and weak perpendicular anisotropies, which is possibly caused by an influence of lattice deformation along the perpendicular direction.