Effect of pre-alloy composition on the content of ferromagnetic phase of MnBi melt spun ribbons

Abstract

The rare-earth-free hard magnetic material MnBi is potential for permanent magnet high-temperature applications with the ferromagnetic phase formed at low temperature (noted as a Low Temperature Phase – LTP). Up to now, the MnBi powders with high LTP content and coercivity have usually been prepared using the melt-spinning technique. However, the large difference in the melting temperature Tm of the two constituents, Mn and Bi, and the strong reactivity of Bi with the copper-based wheel make the preparation of high-performance MnBi ribbons to be difficult. By using a novel approach which creates buffer layers on the inner wall of quartz tube and the cooper wheel surface, we overcame these difficulties and prepared the MnBi ribbons on the conventional commercial melt-spinning furnace ZGK-1. We prepared the melt-spinning MnxBi100-x ribbons with x = 45, 50, 55 and 60. The highest performance of milled ribbons is featured by Hc = 4.52 kOe and Ms = 55 emu/g for x = 55. The influences of pre-alloy compositions on the magnetic properties of MnBi melt - spun ribbons will be discussed in detail.