The permanent magnetic materials market is currently dominated by rare earth element (REE)-based permanent magnets with ideal hard magnetic properties. The REE dependency is considered to be a concern because of the increasing demand for these elements and the corresponding supply constraints. Therefore, an important goal is to find a new permanent magnetic material with fewer or no REEs. The REE free magnetic α-MnBi phase, for example, possesses unique magnetic properties as function of temperature, which makes this material suitable for applications as a permanent magnet for high-temperature environments. Recently, we could show that it is also possible to synthesise the α-MnBi phase by severe plastic deformation and subsequent magnetic field annealing.
To understand how the magnetic field influences nucleation and growth behaviour of the REE free magnetic α-MnBi phase after severe plastic deformation, magnetic field assisted annealing in combination with in-situ high-energy x-ray diffraction measurements was conducted in this study. The magnetic field was realized by two permanent magnets with an inner bore, placed before and behind (in beam direction) an oven with the inert gas sample environment to prevent oxidation. The in-situ annealing measurements reveal unique information on the initial α-MnBi phase formation as well as its development upon annealing. Different initial Mn-Bi materials synthesized with various severe plastic deformation process parameters were studied, which help to understand, how the initial Mn-Bi microstructure affect the formation of the rare-earth free magnetic α-MnBi phase.