Effect of Co-Doping on the Structure, Magnetic and Electronic Properties of Heusler Alloys Mn ₂Fe _1-xCo _xGa (x = 0-1)

Abstract

A series of Mn₂Fe_1-xCo_xGa (x = 0 - 1) Heusler alloys was synthesized by melt-spinning method. The crystal structure, magnetic properties and electronic structure of them were investigated experimentally and theoretically. In undoped Mn₂FeGa, a pure FCC phase is identified, while the substitution of Co for Fe in Mn₂Fe_1-xCo_xGa tends to stabilize the BCC Heusler phase. With the help of melt-spinning technique, single BCC Heusler phase was obtained when x = 0.5-1.0. The FCC Mn₂Fe_1-xCo_xGa are antiferromagnets and their Néel temperatures T_N decrease with Co-doping. But in the BCC phases, a ferromagnetic character is observed and the saturated magnetization M_s at 5K increases rapidly with Co-doping. First-principles calculations suggest that Co-doping can make the formation energy of Mn₂Fe_1-xCo_xGa BCC phase more negative and increase the phase stability, which agrees well with the appearance of the BCC phase in the XRD pattern when Co content is high. This effect can be explained from the fading of the majority DOS peak at EF. The calculated total spin moments of Mn₂Fe_1-xCo_xGa increase from 1.04μB / f.u. for x = 0 to 2.01 μ_B / f.u. for x = 1, following the Slater-Pauling curve of M = Z - 24. The M_s at 5K agrees well with the theoretical results when x = 0.75-1.0. Calculations also suggest that Mn₂Fe_1-xCo_xGa alloys all have 100% or quite high spin polarization ratio. All this makes Mn₂Fe_1-xCo_xGa alloys promising candidates for spintronic applications when Co content is high.

Keywords: Heusler alloys, Magnetic properties, Antiferromagnetic, Half-metal, Electronic structure