Exploring alternative methods of τ-MnAl synthesis 

Permanent magnets are crucial in the production of electric motors, wind turbines, hearing aids, and many other technologies. Rare-earth magnets currently represent the gold standard for commercial magnets in terms of energy product, although they are more expensive to produce than their alternatives. Manganese based systems, like MnBi and MnAl can offer better performance at high temperatures and a lower cost for raw materials. τ-MnAl is specifically comparable to standard rare-earth magnets in terms of cost-to-energy-product ratio. Producing a pure sample of τ-MnAl can be difficult as an ε to ε' to τ path must be followed. In this work, we explore the possibility of increasing sample purities through melting samples in an applied magnetic field. The field is produced by strong neodymium magnets which are arranged to apply an even field across the entire sample. We have found that the field does not greatly reduce impurity phases, although it does suppress certain peaks in the X-ray diffraction pattern of as-cast samples.

• Manganese and aluminum are massed out in a 1:1 molar ratio with 8% excess manganese by mass and arc melted 3 times.

• Field-melted samples are drop cast in the presence of a magnetic field supplied by neodymium magnets.

• Annealed samples are homogenized at 1000° C for 70 minutes, quenched and then heated to 350° C for 13 hours.

• Annealed MnAl sample X-ray diffraction pattern shows only τ phase peaks.

• A possible amorphous phase is visible at from 20 - 37°.

• As-cast samples show τ phase, ε phase, and several impurity phases.

•τ phase, e phase, and impurity phases are present.

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•A possible amorphous phase is visible from 20 - 37°

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•Peaks at 59.3 and 64.8° are suppressed.

• A significant magnetic field can be applied to arc-melted samples using neodymium magnets.

• τ-MnAl can be achieved by annealing arc-melted samples.

• Melting samples in a magnetic field does not significantly reduce impurities, although it may suppress peaks around 59.3 and 64.8°.

• Further work will be done to identify the impurity phases and determine the origin of the peaks which are affected by the field.

[1] Keller, Thomas, et al. "The phase transformation behavior of Mn-Al rare-earth-free permanent magnets." Journal of Magnetism and Magnetic Materials 587 (2023): 171331.

[2] Materials Data on MnBi by Materials Project. United States: N. p., 2020. Web. doi:10.17188/1274398.

[3] Materials Data on MnAl by Materials Project. United States: N. p., 2020. Web. doi:10.17188/1300240.