Competition between cubic and tetragonal phases in all-d-metal Heusler alloys, X _2−x Mn_1+x V (X = Pd, Ni, Pt, Ag, Au, Ir, Co; x = 1, 0): a new potential direction of the Heusler family

Abstract

In this work, a series of all-d-metal Heusler alloys, X 2 − x Mn1 + x V (X = Pd, Ni, Pt, Ag, Au, Ir, Co; x; = 1, 0), were predicted by first principles. The series can be roughly divided into two categories: XMn2V (Mn-rich type) and X 2MnV (Mn-poor type). Using optimized structural analysis, it is shown that the ground state of these all-d-metal Heusler alloys does not fully meet the site-preference rule for classic full-Heusler alloys. All the Mn-rich type alloys tend to form the L21 structure, where the two Mn atoms prefer to occupy the A (0, 0, 0) and C (0.5, 0.5, 0.5) Wyckoff sites, whereas for the Mn-poor-type alloys, some are stable with XA structures and some are not. The c/a ratio was also changed while maintaining the volume the same as in the cubic state to investigate the possible tetragonal transformation of these alloys. The Mn-rich Heusler alloys have strong cubic resistance; however, all the Mn-poor alloys prefer to have a tetragonal state instead of a cubic phase through tetragonal transformations. The origin of the tetragonal state and the competition between the cubic and tetragonal phases in Mn-poor alloys are discussed in detail. Results show that broader and shallower density-of-states structures at or in the vicinity of the Fermi level lower the total energy and stabilize the tetragonal phases of X 2MnV (X = Pd, Ni, Pt, Ag, Au, Ir, Co). Furthermore, the lack of virtual frequency in the phonon spectra confirms the stability of the tetragonal states of these Mn-poor all-d-metal Heusler alloys. This work provides relevant experimental guidance in the search for possible martensitic Heusler alloys in all-d-metal materials with less Mn and new spintronic and magnetic intelligent materials among all-d-metal Heusler alloys.

Theoretical Study of the Electronic and Magnetic Properties and Phase Stability of the Full Heusler Compound Pd2CoAl

“…It is found that the calculated total energy of Pd 2 CoAl in L2 1 -type structure is always smaller than in XA-type structure throughout the whole lattice variation range, which means the L2 1 -type structure is more energetically preferable and should be the ground state. This observation is in a good agreement with the general site preference rule found in other palladium-based Heusler compounds [32,34], i.e., since the Pd atom has more valence electrons than the Co atom, it is more electronegative and prefers the A and C sties. Thus, the L2 1 -type structure is formed for Pd2CoAl.…”

“…However, several recent studies have found many Heusler materials have tetragonal structure as the ground state, e.g., Felser et al [29] found that Mn 3-x Fe x Ga and Mn 3-x Co x Ga have tetragonal structure over the whole range of compositions from experiment results, and then Faleev et al [30,31] performed an extensive investigation on the origin of the tetragonal ground state for 286 Heusler compounds by theoretical calculation, which shows 62% have tetragonal structure. More recently, Han et al [32,33] and Wu et al [34] studied the phase competition between cubic and tetragonal structures in a series of conventional Heusler compounds Pd 2 YZ (Y = Co, Fe, Mn; Z = B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb) and all-d-metal Heusler compounds X 2-x Mn 1+x V (X = Pd, Ni, Pt, Ag, Au, Ir, Co; x = 1, 0) and Zn 2 MMn (M = Ru, Rh, Pd, Os, Ir) and found that many of them also exhibit tetragonal phases, especially the most of Pd 2 Co-based Heusler alloys. Compared with the cubic structures, the tetragonal ones have several special properties, like large perpendicular magnetic anisotropy [35][36][37] and ferromagnetic shape memory behavior [38][39][40][41][42][43], which are very important for the development of spin-transfer torque magnetic random-access memory, ferromagnetic shape memory alloys and other spintronic applications [29,[44][45][46].…”

Perfect Topological Metal CrB2: A One-Dimensional (1D) Nodal Line, a Zero-Dimensional (0D) Triply Degenerate Point, and a Large Linear Energy Range

“…Based on the crystal structure obtained for CrB 2 , the dynamical stability of CrB 2 was examined based on the calculated phonon dispersion along the Γ–M–K–Γ–A–L–H–A paths (see Figure 1 c). Usually, if the system does not contain imaginary frequencies in the phonon dispersion, it can be regarded as having dynamic stability [ 49 , 50 , 51 ]. As shown in Figure 2 , the absence of imaginary frequencies in the first BZ reflects its dynamic stability.…”

Structural configuration and tetragonal phase stability in the equiatomic quaternary Heusler compound TiZnMnSi

“…Thus, the quaternary Heusler with formula XX 0 YZ has stoichiometric ratio of 1 : 1 : 1 : 1 and thus the name of equiatomic quaternary Heusler (EQH) is derived. 22,[48][49][50][51][52][53][54][55][56][57] Both experimental investigations and theoretical calculations have gradually began, e.g., Bainsla et al have prepared the equiatomic quaternary CoFeCrAl Heusler alloy with arc melting technique and found that it exhibits Y-type structure with only a very small amount of anti-site disorder and it has half metallicity with high spin polarization; 52 Paudel et al have theoretically studied the structural, magnetic, electronic and elastic properties for the LiMgPdSb-type EQH alloys CoFeZrZ (Z ¼ Ge, Sb, and Si) and examined their half metallic behaviour under different values of Hubbard correlation parameter U by using GGA+U method; 53 Rani et al have combined a theoretical and experimental study on the half metallic behaviour of EQH alloys CoRuMnGe and CoRuVZ (Z ¼ Al, Ga); 54 Wang et al and Hao et al have designed new EQH compounds ZrRhTiIn and TiZr-RuZ 49 (Z ¼ Al, Ga, In) from rst principle computations; 55 several other works focused on the rare-earth-element based EQH materials, like ScFeCrT (T ¼ Si, Ge), LuCoCrZ (Z ¼ Si, Ge), YCoCrZ (Z ¼ Si, Al, Ge, Ga), MCoVZ (M ¼ Lu, Y; Z ¼ Si, Ge) and they show better prospect for spintronic applications; 51,58,59 and Gao et al conducted a high-throughput screening for spin gapless semiconductors (SGSs) in EQH compounds aer Bainsla et al reported the SGS signature in EQH CoFeMnSi. 48,56,60 Compared with the ternary Heusler materials, the EQH compounds bring out several special advantages, like high composition exibility and better property tunability.…”