Low-energy mechanically milled τ-phase MnAl alloys with high coercivity and magnetization

The high cost of rare earth elements makes the use of high-performance permanent magnets commercially very expensive. MnAl magnetic material is one of the most promising Rare-Earth-free permanent magnets due to its obvious characteristics. However, the coercivity of MnAl alloys produced by melt spinning followed by appropriate treatment is relatively low. In this investigation, a high coercivity up to 5.3 kOe and saturation magnetization of ∼62 emu/g (with an applied magnetic field of 19.5 kOe) were obtained in the mechanically milled τ-phase Mn57Al43 alloy. As milling time goes on, the coercivity firstly increases and then decreases, leading to the formation of knee-point coercivity, while the saturation magnetization decreases simultaneously. The structural imperfections such as disordering and defects play the most important role in the changes of magnetic properties of τ-phase MnAl alloys processed by low-energy mechanical milling. The present results will be helpful for the development of processing protocols for the optimization of τ-phase MnAl alloys as high performance Rare-Earth-free permanent magnets. [Display omitted] •Successful fabrication of pure τ-phase Mn57Al43 alloy by melt spinning and low-energy ball milling processes.•High coercivity (~5.3 kOe) and magnetization (~62 emu/g) were obtained in τ-phase Mn57Al43 alloy.•Disordering and defects play the most important role in the changes of magnetic properties.