CANCELLED TALK - MnAl as an eco-friendly and cost-effective non-rare-earth permanent magnet

Scientists predict that by 2050, every human will have three service robots with over 100 motors inside. Considering the population, the demand for magnetic raw materials would be astronomical which brings low- and non-rare-earth magnets, instead of the rare-earth ones, to the frontier topic. Among different non-rare-earth magnets, MnAl is currently considered a promising family that can fill the gap of (BH)max=10–30 MGOe between the ferrites/Alnico and rare-earth-based magnets.

In the present work, a systematic study of the effect of the substitution of the low amount of Aluminum by Boron according to the formulation of Mn_0.54Al_0.46-xB_x with x ranging from 0 to 0.01 was carried out. Boron was chosen as a dopant because of its low atomic radius and, therefore, the ability to enter the interstitial sites of the MnAl crystal structure. Boron can form AlB₂ and MnB₂ intermetallics which can hinder the growth of grains by acting as pinning centers. Such local confinement of domains can increase the coercivity and alter the material into a hard magnet.

Magnetic properties characterization of melted and non heat treated samples revealed increased remanent magnetization (Mr) and coercivity (Hc) by a small doping amount of Boron. While the measured Mr and Hc of pure MnAl sample were 68.1 and 46.1 kA/m, respectively, 0.1 at. % Boron-doped MnAl had Mr and Hc values 91.3 and 64.9 kA/m, respectively, which shows an increase of 34 % and 41 % compared to the undoped sample. The slope of the increase in the magnetic properties reversed when the amount of Boron dopant surpassed 0.3 at. %. Further reduction in the properties happened by increasing the amount of Boron up to 1 at. %. The current results show that incorporating small amounts of Boron dopant into the structure of MnAl can meaningfully promote magnetic properties.