Effects of Mn and Al addition on structural and magnetic properties of FeCoNi-based high entropy alloys

The effects of Mn and Al additions on the structural stability and magnetic properties of FeCoNi-based alloys were investigated by density functional theory. The simulation results show that adding Al into FeCoNi alloy leads to the transformation of alloy structure from FCC to BCC with B2 structure. The doping of non-magnetic Al reduces the saturation magnetization, regardless alloy structure is FCC, BCC or B2 phase. The FeCoNiMn alloy prefers to form L1(2) structure to diminish the magnetic frustration. In the L1(2) structure, Mn minority spin peak moves from above to below Fermi level, further increasing Mn magnetic moment. For FeCoNi(MnAl)(x) alloys, the alloy structures change from FCC to BCC with the increase of Mn and Al content. The Mn atoms are transformed from antiferromagnetic to ferromagnetic order and the saturation magnetizations are significantly enhanced due to phase transition. It is found that there is obvious short-range order (SRO) in FeCoNi(MnAl)(2) alloy. The SRO parameters are positive between Al-Al, Co-Co, Co-Ni pairs and negative between Ni-Al, Co-Al, Co-Mn, and Mn-Ni pairs. The electronic structure near the Fermi level shows significant difference from random solid structure, which will affect magnetic and electrical properties of FeCoNi(MnAl)(2) alloy.