Theoretical investigations on elastic properties, phase stability, and magnetism in Ni2Mn-based all- d−metal Heusler compounds

The elastic properties, phase stability, and magnetism and correlations among them in all-$d\text{\ensuremath{-}}\mathrm{metal}$ Heusler compounds, i.e., ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ ($T=\mathrm{Sc}$, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, and W) were systematically investigated by first-principles calculations. The results indicated that ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ compounds were not fully consistent with the conventional atomic preferential occupation rule in the Heusler family. Within the scope of Heusler structures, ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ compounds containing early transition metal atoms preferred $L{2}_{1}\text{-type}$ structure, while those with late transition metal atoms were relatively stable in ${\mathrm{Hg}}_{2}\mathrm{CuTi}\text{\ensuremath{-}}\mathrm{type}$ structure. In $d\text{\ensuremath{-}}d$ interatomic hybridization-controlled all-$d\text{\ensuremath{-}}\mathrm{metal} {\mathrm{Ni}}_{2}\mathrm{Mn}T$ Heusler compounds, the atomic radius determined the lattice sizes. Owing to the strong couplings among elastic parameters, phonon modes, and electronic structure, the most likely martensitic phase transition could be expected in weakly magnetic ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ compounds with late transition metal atoms. By applying hydrostatic pressure or imposing chemical pressure via adjusting the composition of Ti in an off-stoichiometric Ni-Mn-Ti system, magnetism was weakened, and the suppressed martensitic phase transition could be re-evoked. In this paper, we also revealed that experimentally observed antiferromagnetism in ${\mathrm{Ni}}_{2}\mathrm{MnTi}$ originated from the arrest of the atomic diffusion process during the transition from the high-temperature chemically disordered paramagnetic state to the low-temperature chemically and magnetically ordered ferromagnetic state, which resulted in the formation of an intermediate metastable and partially disordered antiferromagnetic phase. Comparatively, ${\mathrm{Ni}}_{2}\mathrm{Mn}T$ compounds with early transition metals showed better ductility. In representative ${\mathrm{Ni}}_{2}\mathrm{MnY}$ and ${\mathrm{Ni}}_{2}\mathrm{MnTa}$, it was found that nondirectional $d\text{\ensuremath{-}}d$ interatomic hybridization became prevailing and helped establish the metal bonding character, which consequently enhanced the ductility. This paper can provide more insight into understanding the mechanism of martensitic phase transition and the origin of experimental anomalous magnetic states as well as the scheme to design multiple functional magnetic materials with outstanding ductility in the all-$d\text{\ensuremath{-}}\mathrm{metal}$ Heusler family. Experimentally observed exceptional multicaloric effects in Ni-Mn-based compounds with outstanding mechanical properties make all-$d\text{\ensuremath{-}}\mathrm{metal}$ Heusler compounds attractive for potential solid-state refrigeration application.