Structural and magnetic studies of FexCo1−x(001) alloy films on MgO(001) substrates

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Abstract
Thin epitaxial FexCo1−x alloy films sputtered on MgO(001) substrates were studied by x‐ray scattering and by the magneto‐optical Kerr effect in order to investigate the structural phase stability induced by the substrate and to relate the magnetic properties to the alloy film structure. Alloy films with a thickness of about 20 nm and concentrations from x=1 to x=0.3 exhibit a bcc (001) growth with the in‐plane [100] axis parallel to the MgO[110] axis. For pure Co (x=0) a fcc (001) structure with the Co[100] axis parallel to the MgO[100] axis was obtained. For x=0.15 no out‐of‐plane or in‐plane Bragg peak could be observed, possibly due to the bcc‐fcc structural phase transition. Kerr rotation angles in saturation as a function of x reveal a shape similar to the Slater–Pauling curve. Magnetic hysteresis measurements reveal a fourfold anisotropy with easy axes parallel to the FexCo1−x[100] crystal axis for 1≥x≥0.8, and parallel to the FexCo1−x[110] crystal axis for 0.7≥x≥0.3. In pure Co the easy axis lies parallel to the fcc‐Co[110] crystal axis. Finally, for x=0.28 a step in the magnetic hysteresis in the FexCo1−x[11̄0] direction indicates an overlap of a fourfold and twofold magnetic anisotropy.