Investigation of the site preference in Mn₂RuSn using KKR-CPA-LDA calculation

We investigated the site preference and atomic disorder between the A and C sites in Heusler alloy Mn₂RuSn by using the KKR-CPA-LDA method. It is found that, at ground state 0 K, the Hg₂CuTi-type (XA) structure is energetically favored, in which one Mn and one Ru occupy the A and C sites, respectively. The ground state energy of Mn₂RuSn increases with increasing degree of Mn (A)–Ru (C) atomic disorder. The equilibrium lattice constants also show a similar tendency. The Mn (A)–Ru (C) disorder lower the total spin moment effectively, which is 1.87 μ_B in the XA structure and only 0.98 μ_B in the L2₁B structure. In Mn₂RuSn with different degree of Mn (A)–Ru (C) atomic disorder, the total moments are always determined by the antiparallel aligned Mn (A, C) and Mn (B) spin moments. The saturated moment of Mn₂RuSn at 5 K is 1.68 μ_B, which corresponds to ∼11% antisite Mn entering the C site. This Mn (A)–Ru (C) disorder in samples can be related to the contributions from entropy of mixing at elevated temperatures, especially when this sample is quenched from high temperatures. - Highlights: • Atomic disorder in Heusler alloy Mn₂RuSn has been investigated by the KKR-CPA method. • Hg₂CuTi-type structure is energetically favored in Mn₂RuSn. • Mn (A)–Ru (C) disorder obviously influence the magnetic properties of Mn₂RuSn