Evidence of exchange coupling in τ-MnAlC/FeCo system

Scientific and technological analysis of exchange-spring magnets: Applications and trends

“…The results demonstrated strong exchange coupling between Mn 54.3 Al 44 C 1.7 particles and α-Fe within the composite produced. [ 59 ] Mn 53.3 Al 45 C 1.7 /Fe 65 Co 35 (95/5 wt%) 76 33 0.277 5.57 In this work, the Thamm-Hesse analysis revealed the presence of exchange coupling in the nanocomposite sintering at 773 K during 30 min, presenting the best hard magnetic properties. The reduction in maximum energy product was correlated with the decrease in the weight fraction of the phase in the sample.…”

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

“…This was intentionally decided so the arc did not interact directly with the molten Mn at the beginning of melting process. In addition, an extra amount of Mn (3.0 wt.%) was added to compensate the Mn that evaporates during the melting processes [ 32 , 33 ].…”

“…The thermal procedure to transform the RT ε -MnAlC to the τ -MnAlC phase takes into account two fundamental parameters: the annealing temperature and time [ 4 , 8 , 12 , 13 ]. In our study, we set the annealing temperature at 550 °C, according to a previous study [ 33 ] and varied the annealing time (15, 20 and 30 min) in order to find the suitable condition to produce a virtually pure τ -MnAlC alloy. A scheme of the annealing process is shown in Figure 2 a.…”

“…Some of the most attractive routes to optimize the magnetic properties of a τ -MnAlC magnet are mechanical milling [ 4 ]; hot extrusion [ 30 ]; hot pressing [ 31 ]; mixtures with other elements such as Mn 65 Ga 35 [ 26 ]; exchange springing with soft magnetic phases such as –Fe [ 32 ], Fe 65 Co 35 [ 33 , 34 ] and MnB [ 35 ]; and thin film processes [ 36 ]; and each of them has advantages and disadvantages. For instance, the hot extrusion method allows the production of highly anisotropic MnAl-C-Ni magnets with a high magnetic energy (BH) max = 43 kJ/m 3 [ 30 ], but it uses an expensive process that is not suitable for large-scale production; mechanical milling is a cost-effective and efficient process to improve the magnetic performance of MnAl alloys with nanocrystalline microstructures [ 37 , 38 ], and is beneficial for increasing the coercivity ( H c = 0.5 T [ 38 ]), but it produces a large amount of equilibrium phases after the thermal treatment following the milling process, leading to reduced magnetization [ 4 , 39 ].…”