The phase transformation behavior of Mn-Al rare-earth-free permanent magnets

• Published in: Journal of magnetism and magnetic materials 2023-12, Vol.587, p.171331, Article 171331
• Main Authors: Keller, Thomas, Barbagallo, Dylan, Sheremetyeva, Natalya, Ghosh, Tushar Kanti, Shanks, Katherine S., Hautier, Geoffroy, Baker, Ian
• Format: Article
• Language: English
• Subjects: Density Functional Theory; Electron Backscatter Diffraction; Mn-Al; Ordering; Phase Transformation; Synchrotron Diffraction
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2023.171331

[Display omitted] •The ε to τ phase transformation was studied in-situ using XRD, DSC, and T-VSM.•DFT and DSC concurred that the ε to ε’ to τ pathway is energetically favorable.•Annealing ε at 350 °C showed ε’ is ferromagnetic, in agreement with DFT.•A boundary front of ε’ was observed between the τ and ε phases at 350 °C.•The ε to ε’ to τ path has lower activation energies than ε to τ, kinetic advantage. Rare-earth-free permanent magnet materials based on Mn show great promise for applications in electric motors and devices. The metastable ferromagnetic τ phase of the Mn-Al system has magnetic properties between those of the high-performance Nd-Fe-B magnets and the lower-performance ferrite magnets. However, the hybrid displacive-diffusional pathway of τ formation, from the parent ε phase through the intermediary ε’ phase, is still not fully understood. This phase transformation progression was studied in-situ using diffractive, calorimetric, and magnetometric techniques to show that the progression from ε to τ in Mn54Al46 at