Structural, electronic and magnetic properties of χ-carbides Fe 5-xMnxC2 (x = 1-5) from density-functional theory calculations

Using first-principles technique, the electronic structures of χ-carbides Fe5−xMnxC2 (x = 1–5) are studied. There exists charges transfer from metal cation to C atoms in χ-carbides, and this reveals an ionic contribution to the bonds. The calculated formation energy of Fe5C2 is 0.136 eV/f.u. and the formation energy of Mn5C2 is −0.257 eV/f.u. The energy stability of Mn4FeC2, the formation energy as −0.281 eV/f.u, is higher than other χ carbides (Fe,Mn)5C2. The average magnetic moments of Fe5−xMnxC2 (x = 1–5) are also calculated. The magnetic moments (Ms) of metal atoms in the different site are different in χ carbides. The Ms of FeI, FeII and FeIII in Fe5C2 are 2.18, 1.72 and 1.16 μB/atom respectively. The Ms of MnI, MnII and MnIII in Mn5C2 are 2.44, −0.50 and −1.44 μB/atom respectively. The magnetic moment of MnI is positive, but the magnetic moments of MnII and MnIII are negative in χ-Mn5C2.