Abstract
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 0K, 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 1.87μB in the XA structure and only 0.98μB 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 5K is 1.68μB, 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.
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