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.

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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