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Optimized Route for the Fabrication of MnAlC Permanent Magnets by Arc Melting.

Hugo Martínez SánchezJuan David GámezJosé Luis ValenzuelaHernan Dario ColoradoLorena MarínLuis Alfredo RodríguezEtienne SnoeckChristophe GatelLigia Edith ZamoraGerman Antonio Pérez AlcázarJesús Anselmo Tabares
Published in: Molecules (Basel, Switzerland) (2022)
The rare-earth-free MnAlC alloy is currently considered a very promising candidate for permanent magnet applications due to its high anisotropy field and relatively high saturation magnetization and Curie temperature, besides being a low-cost material. In this work, we presented a simple fabrication route that allows for obtaining a magnetically enhanced bulk τ -MnAlC magnet. In the fabrication process, an electric arc-melting method was carried out to melt ingots of MnAlC alloys. A two-step solution treatment at 1200 °C and 1100 °C allowed us to synthesize a pure room-temperature ε -MnAlC ingot that completely transformed into τ -MnAlC alloy, free of secondary phases, after an annealing treatment at 550 °C for 30 min. The Rietveld refinements and magnetization measurements demonstrated that the quenched process produces a phase-segregated ε -MnAlC alloy that is formed by two types of ε -phases due to local fluctuation of the Mn. Room-temperature hysteresis loops showed that our improved τ -MnAlC alloy exhibited a remanent magnetization of 42 Am 2 /kg, a coercive field of 0.2 T and a maximum energy product, (BH) max , of 6.07 kJ/m 3 , which is higher than those reported in previous works using a similar preparation route. Experimental evidence demonstrated that the synthesis of a pure room-temperature ε -MnAlC played an important role in the suppression of undesirable phases that deteriorate the permanent magnet properties of the τ -MnAlC. Finally, magnetic images recorded by Lorentz microscopy allowed us to observe the microstructure and magnetic domain walls of the optimized τ -MnAlC. The presence of magnetic contrasts in all the observed grains allowed us to confirm the high-quality ferromagnetic behavior of the system.
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