Control of anisotropy and magnetism of MnBi nanomaterials

ORAL

Abstract

High-anisotropy MnBi nanostructures have been fabricated by in-situ annealing of Bi/Mn/Bi multilayers and magnetic-field annealing of melt-spun Mn$_{\mathrm{x}}$Bi$_{\mathrm{100-x}}$ ribbons. The ratio of Mn to Bi affects the concentration of NiAs-type MnBi, the degree of c-axis orientation, and phase distribution. For x $=$ 50, the Mn$_{\mathrm{x}}$Bi$_{\mathrm{100-x}}$ film exhibits the optimum nanostructure in which MnBi grains are uniformly separated by a thin layer of Bi. This has produced a record value of \textit{(BH)}$_{max} = $ 16.3 MGOe for this compound. A good c-axis texture has been developed for Mn$_{50}$Bi$_{50}$ ribbons with a remanence ratio of 0.94 after magnetic-field annealing and this result subsequently leads to \textit{(BH)}$_{max} = $ 9.2 MGOe, the highest value for bulk MnBi materials. The reason for the much higher energy product for the Mn$_{50}$Bi$_{50}$ film compared to the Mn$_{50}$Bi$_{50}$ ribbon is that the ribbon has a comparatively lower coercivity induced by inhomogeneous distribution of intergranular Bi. The effect of element doping, optimization of preparation parameters, and temperature dependence of properties also will be discussed.

*This work was supported by US DOE/BES (DE-FG2-04ER46152) and NCMN.

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Authors

  • W. Zhang

    • Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588
    • Nebraska Center for Materials and Nanosceince and Department of Physics and Astronomy, University of Nebraska
    • Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE

  • David Sellmyer

    • Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE 68588
    • Nebraska Center for Materials and Nanosceince and Department of Physics and Astronomy, University of Nebraska
    • NCMN, University of Nebraska, Lincoln, NE 68588
    • Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, NE
    • University of Nebraska, Lincoln, NE 68588