Effect of Co-doping on the structure, magnetic and electronic properties of Heusler alloys Mn2Fe1-xCoxGa (x = 0–1)

Abstract

A series of Mn2Fe1-xCoxGa (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. The substitution of Co for Fe in Mn2Fe1-xCoxGa tends to stabilize the BCC Heusler phase, with the help of melt-spinning technique, single BCC Heusler phase was obtained within the range of × = 0.5–1.0. The FCC Mn2Fe1-xCoxGa are antiferromagnetic and their Néel temperatures TN decrease with Co-doping. But in BCC Mn2Fe1-xCoxGa, a ferromagnetic character is observed and the saturated magnetization Ms at 5 K increases rapidly with increasing Co content. First-principles calculations suggest that Co-doping can make the formation energy of Mn2Fe1-xCoxGa 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 change of electronic structure with Co-doping. The calculated total spin moments of Mn2Fe1-xCoxGa increase from 1.04μB / f.u. for × = 0 to 2.01 μB / f.u. for × = 1, following the Slater-Pauling curve of M = Z −24. The Ms at 5 K agrees well with the theoretical results when × = 0.75–1.0. Calculations also suggest that Mn2Fe1-xCoxGa alloys all have 100% or quite high spin polarization ratio. All this makes them promising candidates for spintronic applications when Co content is high.