Effects of a static magnetic field on solidification structure of MnBi phase in semi-solidified Bi-Mn alloy

Influences of a static magnetic field (0-1.0 T) on the solidification structure and magnetic property of the semi-solidified Bi-3%Mn and Bi-6%Mn alloys have been investigated. In the present of the magnetic field, the alloys were maintained at semi-solid state for a certain time and then solidified. It was shown that alignment and preferential growth of MnBi crystals along the applied field occurred. The alignment degree of MnBi was increased with the increase of the applied field, and the mean length of elongated MnBi crystals was increased with the increase of the applied field and the prolongation of solidification time. Moreover, the remained magnetic flux intensity along the aligned direction of Bi-Mn alloys in the case with a magnetic field was found to be strongly anisotropic and nearly double of that without magnetic field. A model was proposed to explain the alignment and preferential growth of ferromagnetic MnBi crystals in a magnetic field in terms of the magnetic anisotropism and the interaction between the crystals.