Magnetism and Magneto-Electric Transport in Amorphous Iron-Germanium Thin Films*

In amorphous iron-germanium films (a-Fe_xGe_1-x), local spin-orbit coupling and broken inversion symmetry yield a local Dzyaloshinskii-Moriya (DM) interaction, which manifests itself in distinctly non-square hysteresis loops. We present magnetization, Hall effect, and electrical resistivity measurements of thin films (50-80nm in thickness) of a-Fe_xGe_1-x with 0.45 < x < 0.65. The films are magnetic over the entire composition range investigated, and exhibit a significant anomalous Hall effect. As with films of amorphous iron-silicon, we ascribe these findings to the local DM interaction, and to the increased importance of the orbital magnetism in amorphous materials, which is equivalent to a localized Berry phase curvature.