The first-principles study of martensitic transformations in MnMe (Me = Rh, Pd) alloys at low temperatures

The structural, elastic, phonon, thermal and electronic properties of MnMe are investigated by the first-principles calculations. The predicted phase stability trends due to structural energy differences are consistent with those observed experimentally. The obtained negative shear modulus (C′ = (C11 – C12)/2) of paramagnetic B2 (PM-B2) phases triggers the cubic to tetragonal distortion. The calculated phonon dispersions without negative frequency indicate that antiferromagnetic L10 (AFM-L10) together with paramagnetic L10 (PM-L10) structures are dynamically stable, and the PM-L10 → AFM-L10 transition is caused by magnetism rather than lattice dynamics. Debye temperatures, anisotropy and Poisson's ratios are also first evaluated. The calculated results show that the collinear antiferromagnetic states (CuAu-I type) are mechanically and dynamically stable, thus are the low temperature phases.