effect of annealing temperature and composition on magnetic properties of manganese-bismuth homogenized in tube furnace

Repeated heat treatment on manganese-bismuth (mnbi) in a tube furnace increases the homogeneity of rare-earth-free magnets. ferromagnetic low temperature phase (ltp) mnbi is formed after heating mn and bi in a ratio of 2:1 at 1000 °c for 1 h and then 400 °c for 1 h. areas with comparable compositions of mn and bi are detected, but some mn and bi remains segregate after using this stepped heating 3 times. the subsequent annealing at 340 °c gives rise to higher magnetizations and coercivity than those using 410 °c annealing. increasing the starting mn:bi ratio to 4:1 reduces the coercivity and remanent magnetization due to the increase in mn oxidation at the expense of ferromagnetic phase.