Phase Transition and Electronic Structures of All- d-Metal Heusler-Type X2MnTi Compounds (X = Pd, Pt, Ag, Au, Cu, and Ni)

Abstract

In this work, we investigated the phase transition and electronic structures of some newly designed all-d-metal Heusler compounds, X₂MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni), by means of the first principles. The competition between the XA and L2₁ structures of these materials was studied, and we found that X₂MnTi favors to feature the L2₁-type structure, which is consistent with the well-known site-preference rule (SPR). Under the L2₁ structure, we have studied the most stable magnetic state of these materials, and we found that the ferromagnetic state is the most stable due to its lower energy. Through tetragonal deformation, we found that the L2₁ structure is no longer the most stable structure, and a more stable tetragonal L1₀ structure appeared. That is, under the tetragonal strain, the material enjoys a tetragonal phase transformation (i.e., from cubic L2₁ to tetragonal L1₀ structure). This mechanism of L2₁-L1₀ structure transition is discussed in detail based on the calculated density of states. Moreover, we found that the energy difference between the most stable phases of L1₀ and L2₁, defined as ΔE _M (ΔE _M = E _Cubic-E _Tetragonal), can be adjusted by the uniform strain. Finally, the phonon spectra of all tetragonal X₂MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni) phases are exhibited, which provides a powerful evidence for the stability of the tetragonal L1₀ state. We hope that our research can provide a theoretical guidance for future experimental investigations.

Keywords: DFT; Heusler alloys; electronic properties; electronic structure; spintronic.