Chitnarong Sirisathitkul - Division of Physics, School of Science, Walailak University
Patchara Sukonrat - Office of Scientific Instrument and Testing, Prince of Songkla University
Pongsakorn Jantaratana - Department of Physics, Kasetsart University
Thanida Charoensuk - Walailak University

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 ۲:۱ at ۱۰۰۰ °C for ۱ h and then ۴۰۰ °C for ۱ h. Areas with comparable compositions of Mn and Bi are detected, but some Mn and Bi remains segregate after using this stepped heating ۳ times. The subsequent annealing at ۳۴۰ °C gives rise to higher magnetizations and coercivity than those using ۴۱۰ °C annealing. Increasing the starting Mn:Bi ratio to ۴:۱ reduces the coercivity and remanent magnetization due to the increase in Mn oxidation at the expense of ferromagnetic phase.

MnBi, Rare-earth-free magnet, Coercivity, Remanent magnetization, Tube furnace