MWCNT reinforced τ-Mn-Al nanocomposite magnets through spark plasma sintering

We herein exploit the inherent benefits of both multi-walled carbon nanotubes (MWCNTs) and spark plasma sintering (SPS) for augmenting the performance of rare-earth free Mn56Al44 permanent magnets through grain refinement and stabilization of τ-phase. A good combination of remanent magnetization, coercivity and energy product values: 42.5 emu/g, 3.22 kOe and 1.92 MGOe; and 45.6 emu/g, 3.64 kOe and 2.26 MGOe were achieved for the SPSed Mn-Al magnets with 1.5 and 2 wt % additions of MWCNTs, respectively. The observed coercivity enhancement in the SPSed Mn-Al/MWCNT nanocomposite magnets is hypothesized to originate from the domain-wall pinning, as a consequence of precipitation of MWCNTs in the form of broken nanotubes and amorphous carbonaceous material at the grain boundaries. Although, a more detailed study is essential to verify the above fact, the present strategy provides a new basis for producing high performance rare earth free Mn-Al permanent magnets in a simpler way using the SPS process.