Competition of L21 and L10 ordering in Pd2MnSe, Pd2FeSe, Pd2MnTe and Pd2FeTe Heusler alloys

Abstract

Based on first-principles method, for Pd2MnSe, Pd2FeSe, Pd2MnTe and Pd2FeTe, we investigated the competition between cubic L21-type and their tetragonal L10-type ordering. Firstly, low-energy tetragonal ground states are found in these alloys during the tetragonal deformation. By regulating the c/a ratio under the fixed volume of equilibrium cubic phase, we obtain two minimums in total energy-c/a curve: a shallow one in c/a 1. Meanwhile the uniform strain is also taken into consideration in this work, and we found that ΔEM and Vopt + X%Vopt are negatively correlated, that is, with the volume increases from Vopt − 3%Vopt to Vopt + 3%Vopt, the absolute value of ΔEM decreases accordingly. Secondly, the origin of the tetragonal ground states of Pd2 [Fe/Mn][Se/Te] are also be explained by the density of states (DOS) figures. From the valley-and-peak structure, we can find the DOS at or in the vicinity of the Fermi level is much broader and shallower in tetragonal L10 state than cubic L21 state, indicating the phase stability of tetragonal L10 phases of these Pd2-based alloys. Moreover, to further study the competition of L21 and L10 ordering in these alloys and verify the stability of the tetragonal L10 state, elastic constants were introduced in this work, C11, C12 and C44 for cubic state while C11, C12, C13, C33, C44, C66 for tetragonal L10-type structure. According to the judgment basis, all alloys exhibit L10-stable, satisfying our conclusions about the stability of tetragonal states. We hope our work can provide a guidance for researchers to further explore and study new magnetic functional tetragonal materials among the full-Heusler alloys. Keywords: L21 and L10 ordering, Tetragonal ground state, Elastic constant