Abstract
High‐anisotropy NiAs‐type MnBi films are produced by in situ annealing of Bi/Mn/Bi trilayers, [Bi/Mn/Bi]n multilayers, and subsequent magnetic field annealing. Phase components, crystallographic anisotropy, and magnetic properties of the MnxBi100−x thin films exhibits strong dependence on Mn concentration. High‐purity MnBi thin films with perfect c‐axis orientation are obtained by carefully controlling the Mn/Bi ratio. An energy product of 16.3 MGOe, which is the highest value reported so far, is achieved for the x = 50 film of thickness t = 100 nm. The MnBi thick film (t = 2 μm) changes from isotropic to anisotropic after magnetic field annealing. Depending on the direction of the applied field during magnetic field annealing, the MnBi thick film may have out‐of‐plane or in‐plane anisotropy. This control of anisotropy direction enables applications of MnBi films in permanent‐magnet, spintronic devices, or magnetic micro‐electro‐mechanical systems. In addition, the room‐temperature magnetocrystalline anisotropy constant and saturation polarization of the hard magnetic MnBi phase are determined to be K = K1 + K2 = 15.0 Mergs cm−3 and Js = 8.2 kG, respectively.
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