Structural, elastic, phonon, and electronic properties of MnPd alloy

The structural, elastic, phonon, and electronic properties of MnPd alloy have been investigated by using the first-principles calculations. The calculated lattice constants and electronic structure are in good agreement with the experimental results. The microscopic mechanism of the diffusionless martensitic transition from the paramagnetic B2 (PM-B2) phase to the antiferromagnetic L1₀ (AFM-L1₀) phase through the intermediate paramagnetic L1₀ (PM-L1₀) phase has been explored theoretically. The obtained negative shear modulus C′= (C₁₁-C₁₂)/2 of the PM-B2 phase is closely related to the instability of the cubic B2 phase with respect to the tetragonal distortions. The calculated phonon dispersions for PM-L1₀ and AFM-L1₀ phases indicate that they are dynamically stable. However, the AFM-L1₀ phase is energetically most favorable according to the calculated total energy order, so the PM-L1₀ !AFM-L1₀ transition is caused by the magnetism rather than the electron–phonon interaction. Additionally, the AFM-L1₀ state is stabilized through the formation of a pseudo gap located at the Fermi level. The calculated results show that the CuAu-I type structure in the collinear antiferromagnetic state is dynamically and mechanical stable, thus is the low temperature phase.