The demand for rare-earth elements is currently outstripping supply and leading to what is known popularly in the press as the "rare earth crisis" (Lewis, L. H. & Jiménez-Villacorta, F. Metall. Mater. Trans. A 44, 2–20 (2012). This demand arises from the many applications for rare-earth elements including the rare-earth-based "supermagnets", materials for military applications, and alternative energy technologies. To that end, we seek to produce nanostructured permanent magnets that produce anisotropies and energy products that are comparable to those of the current supermagnets using only cheap, abundant and more sustainably-produced metals.
One example we are working on is to combine τ-MnAl with α-Fe at the nanoscale to produce an exchange-spring magnet with better performance than its constituent materials. The τ-phase of MnAl is metastable, but is ferromagnetic with high coercivity. We are able to produce this phase through the rapid solidification of molten MnAl through melt-spinning (Jiménez-Villacorta, F. et al. ; Jiménez-Villacorta, F. et al. Metals (Basel). 4, 8–19 (2014). The soft but highly magnetic α-Fe phase is then mixed with τ-MnAl at the nanoscale through high energy ball milling, to produce exchange-spring coupling.
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| Phase and magnetic diagram at the near-equiatomic region of Al-Mn alloys. From Jiménez-Villacorta, F. (2012). | Room temperature M(H) curve taken for Mn53.8Al46.2. The paramagnetic signal was linearly fit and subtracted to obtain a corrected FM signal. By comparing the MS of this sample to the theoretical MS of τ-MnAl, it is determined that the sample contains ~21 wt% τ-phase. |