The structural, elastic, phonon, thermal and electronic properties of MnX (X=Ni, Pd and Pt) alloys: First-principles calculations

We present first-principles studies of structural, elastic, phonon, thermal and electronic properties of MnX. According to the calculated total energies, the predicted phase stability trends are consistent with previous experiments. For the L10 lattice, the calculated Mn–Mn exchange couplings JMn–Mns, depending on the valence electron concentration Cv, have been investigated. The dominant inter-layer nearest-neighbors coupling J1L and in-plane next-nearest-neighbor coupling J2 are responsible for the differences in energy between the two structural phases (T=0 K). The negative shear modulus C′ of the paramagnetic B2 (phase) triggers the cubic to tetragonal distortion. The calculated phonon dispersions indicate that the primary driving force for the paramagnetic L10 to antiferromagnetic L10 transition is the magnetic ordering energy, rather than some entropic contribution from thermal vibrations. The Debye temperatures, anisotropy and Poisson's ratio are also assessed. The calculated results show that the collinear antiferromagnetic CuAu-I type structures are mechanically and dynamically stable, and agree with the empirical ground states.

► Predicted phase stability trends due to structural energy differences are confirmed. ► Softening of (C11–C12)/2 triggers the cubic to tetragonal phase transformation. ► Obtained phonon curves and DOS at EF reveal that AFM-L10 is most stable. ► The Debye temperature, anisotropy and Poisson's ratio are first assessed.