Structural and magnetic properties of rapidly solidified and Bi-bonded hot compacted Mn53.3−xAl45C1.7Tix magnets

Abstract

This study examines the impact of Ti doping on the phase formation and magnetic properties of Mn–Al–C alloys. Using melt spinning, we synthesized Mn${}_{53.3-x}$Al₄₅C_1.7Ti${}_x$ alloys (x values ranging from 0 to 1.5) producing high purity $ϵ$-phase ribbons. The optimal annealing treatment for the formation of ferromagnetic $\tau$-phase is 20 min at 550 °C for all compositions. However, Ti-doped samples showed the formation of $\beta$-phase due to partial phase decomposition, and TiC precipitates were present at high Ti concentrations. Upon doping, the Curie temperature was increased from 557K (Ti free sample) to 600K. To improve the coercivity, a combination of ball milling and hot compaction, introducing Bi as a metallic binder, have resulted in increased coercivity from 0.18 T to 0.33 T. Bi addition lead to formation of a grain boundary phase aiding densification. We demonstrate how modifying composition and processing can improve the magnetic properties of Mn–Al based magnets.