Effects of film composition and substrate orientation on the structure and the magnetic properties of Fe-Co-B alloy films formed on MgO single-crystal substrates
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(Fe0.7Co0.3)100−x B x alloy thin films are prepared on MgO single-crystal substrates with (100), (110), and (111) orientations at 200C by ultra-high vacuum radio-frequency magnetron sputtering with various B compositions, x, from 0 to 15 at.%. The effects of composition and substrate orientation on the structure and the magnetic properties are studied. Fe-Co epitaxial films with bcc structures are obtained on all substrates. Fe-Co(100) single-crystal films are formed on MgO(100) substrates. Fe-Co films epitaxially grown on MgO(110) substrates consist of two (211) variants whose orientations are rotated around the film’s normal by 180 each other. Fe-Co(110) films grow epitaxially on MgO(111) substrates with two types of variants, Nishiyama-Wasserman and Kurdjumov-Sachs relationships. As the B composition increases up to around 5 at.%, the film involves an amorphous structure in addition to an epitaxial bcc crystal structure. With further increases in the B content, the film is only amorphous. The magnetization properties of the films involving epitaxial crystals reflect the magnetocrystalline anisotropy of the bulk Fe-Co crystal. The easy magnetization direction varies depending on the crystallographic orientation of the film. Isotropic in-plane magnetic properties are observed for amorphous films.
KeywordsFe-Co Fe-Co-B Thin film Epitaxial growth Single-crystal substrate MgO
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