Structure, growth characteristic and magnetic properties in directionally solidified Bi-MnBi composite under strong magnetic field

Bi-MnBi composite has been directionally solidified to investigate the influence of a strong magnetic field on its microstructure, growth characteristics and magnetic properties. Experimental results show that MnBi eutectic fiber is aligned, regularized and coarsened during directional solidification under an axial strong magnetic field. In particular, the alignment of irregular eutectic fiber under a magnetic field may offer a new method to prepare regular fiber composite and extend the range of uses of such composite. It has also been found that the strong magnetic field has modified the growth mode of the MnBi fiber and enhanced the transition from non-faceted to faceted. The distribution of the solute Mn in front of the MnBi fiber at the liquid-solid interface has been measured and the result shows that the magnetic field has enhanced the enrichment of the solute Mn in front of the MnBi fiber. Moreover, magnetic measurement reveals a pronounced promotion of the magnetic anisotropy and the remanence (Br) under the magnetic field. Based on these experimental results, a simple theory of solute enrichment in front of a ferromagnetic fiber and fiber coarsening under a strong magnetic field has been proposed.