Enhanced formation and improved thermal stability of ferromagnetic τ phase in nanocrystalline Mn55Al45 alloys by Co addition

Investigation on magnetic properties of mechanically alloyed τ-MnAlC with Fe addition

“…Indeed, among L10 ferromagnetic materials, metastable τ-MnAl has high c/a ratio (c/a ≈ 1.3) compared to other more stable ones, namely, L10 -NiFe (c/a ≈ 1) [19], L10 -CoPt (c/a ≈ 0.97) [20], L10 -FePt (c/a ≈ 0.96) [21] . The reduction of c/a ratio that led to an improvement in thermal stability of τ-MnAl is in agreement with the results and conclusion reported by [9,10] when Ni and Co were added. In detail, in case of Ni doping, from up to nearly 2 at.% of Ni doping, c/a ratio decreased with an enhancement in thermal stability of τ-MnAlNi alloy, whereas from 4 to 6 at.% of Ni doping, the thermal stability was reported to be decreased accompanied with an increase in c/a ratio [9].…”

“…Therefore, a reduction in lattice parameters (Table 1) when Fe was added into τ-MnAlC alloys should be the reason for such in magnetization. Indeed, similar observation can be found when MnAl(C) was doped with different TM element such as Ni, Co, and Cu [8][9][10]. In addition, it is in accordance with the enhancement of Ms in case of Fe doped MnAl thin films when the lattice parameters increased to the optimal values [7].…”

“…From the DSC curves Figure 4, one can notice that there is a shift of the peaks to higher temperature region, which is demonstrated through the increment of Tpeaks, showing an enhancement in thermal stability of the ε phase, as also reported in case of doping Co and Ni [9,10]. Furthermore, from the XRD diagram of aged samples, it is seen that the transformation from ε phase to τ phase was completed since the ε phase no longer existed after the aging process.…”

“…In detail, in case of Ni doping, from up to nearly 2 at.% of Ni doping, c/a ratio decreased with an enhancement in thermal stability of τ-MnAlNi alloy, whereas from 4 to 6 at.% of Ni doping, the thermal stability was reported to be decreased accompanied with an increase in c/a ratio [9]. In case of Co doping, the c/a ratio decreased monotonically from 1.285 of Co-free sample to 1.275 corresponding to 3 at.% of Co doping, being reported to strengthen the thermal stability of τ-MnAlCo alloy [10].…”

“…More interestingly, although the addition of Ni or Co into τ-MnAl did not improve the magnetic properties of τ-MnAl phase, its thermal stability was enhanced, which is also an important factor for L1o ferromagnetic materials' application [9][10][11].…”