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

ORAL

Abstract

Thin films (65 < t < 100nm) of amorphous cobalt- and iron-germanium (a-CoxGe1-x and a-FexGe1-x) with 0.40 < x < 0.61 exhibit similar electrical resistivity but remarkably different magnetization for a fixed transition metal concentration x. For all compositions investigated, the resistivity depends weakly on temperature but strongly on x, with only slight differentiation between the Fe and Co transition metal species. However, a low-temperature upturn in resistivity associated with resonant impurity scattering is observed in a-FexGe1-x but absent in a-CoxGe1-x, due to their different magnetic properties: where all measured compositions of a-FexGe1-x are itinerant ferromagnets with a Curie temperature that increases with x, a-CoxGe1-x is paramagnetic down to T = 2 K in the same composition range. This behavior parallels these materials’ crystalline cousins: B20 FeGe hosts a rich magnetic phase diagram, while B20 CoGe is paramagnetic thanks to a pseudogap just above the Fermi level in its density of states. The long-range order that enables this explanation in those materials is absent in our amorphous films, leading us to ascribe the magnetic behavior of these alloys to more localized, short-range physics.

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Presenters

  • Dinah Simone Bouma

    Department of Physics, University of California, Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory

Authors

  • Dinah Simone Bouma

    Department of Physics, University of California, Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory

  • Frank Bruni

    Department of Physics, University of California, Berkeley

  • Robert Streubel

    MSD, Lawrence Berkeley National Laboratory, Lawrence Berkeley National Laboratory, Materials Sciences Division, Lawrence Berkeley National Laboratory

  • Xiaoqian M Chen

    Materials Sciences Division, Lawrence Berkeley National Laboratory, and University of Kentucky, Lawrence Berkeley National Laboratory and University of Kentucky

  • Sujoy Roy

    Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA, Advanced Light Source, Lawrence Berkeley National Laboratory, ALS, Lawrence Berkeley National Laboratory

  • Noah Kent

    Lawrence Berkeley National Lab, UC Santa Cruz/ LBNL, Lawrence Berkeley National Laboratory, Materials Sciences Division, Lawrence Berkeley National Laboratory, and Department of Physics, University of California, Santa Cruz

  • Zhanghui Chen

    Materials Sciences Division, Lawrence Berkeley National Laboratory, Lawrence Berkeley National Laboratory

  • Lin-Wang Wang

    Lawrence Berkeley National Laboratory, Materials Sciences Division, Lawrence Berkeley National Laboratory

  • Peter Fischer

    UC Santa Cruz/ LBNL, Lawrence Berkeley National Laboratory, Materials Sciences Division, Lawrence Berkeley National Laboratory, and Department of Physics, University of California, Santa Cruz

  • Stephen Douglas Kevan

    Advanced Light Source, Lawrence Berkeley National Laboratory

  • Frances Hellman

    Physics and Materials Science and Engineering, UC Berkeley, Physics, University of California, Berkeley, University of California, Berkeley, Department of Physics, University of California, Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory