Impact of magnetic and antisite disorder on the vibrational densities of states in Ni2MnSn Heusler alloys

We have performed a combined experimental and theoretical investigation of the vibrational properties of Ni2MnSn Heusler alloys. Sn-partial vibrational density of states (VDOS) of 119Sn was measured by nuclear resonant inelastic x-ray scattering at temperatures of 15 and 300 K, while magnetism and local environment of Sn was resolved by 119Sn Mössbauer spectroscopy. Using density functional theory, we associate the peaks in the VDOS with particular features in the element-resolved phonon dispersion of L21 ordered Ni2MnSn. The good agreement between theory and experiment in the low-energy region provides the evidence that the inversion of optical modes at Γ involving the displacement of Ni and the heavier main group element atoms, which was predicted previously for other Ni-Mn-based Heusler compounds, is also a characteristic property of Ni2MnSn. Introducing different types of magnetic and antisite disorder in our calculations results in a distinctive redistribution and broadening of the Sn-VDOS, suggesting that considering partial disorder further improves the agreement with the experiment in particular at the highest phonon energies

Superconducting and antiferromagnetic properties of dual-phase V3Ga

The binary compound V3Ga can exhibit two near-equilibrium phases, the A15 structure that is superconducting and the Heusler D03 structure that is semiconducting and antiferromagnetic. Density functional theory calculations show that these two phases are nearly degenerate, being separated in energy by only ±10  meV/atom. Our magnetization measurements on bulk-grown samples show antiferromagnetism and superconducting behavior below 14 K. These results indicate the possibility of using V3Ga for quantum technology devices exploiting the co- existence of superconductivity and antiferromagnetism in a dual-phase material.Superconductivity and magnetism were once thought to be mutually exclusive because magnetic fields are efficient at closing the superconducting gap. Nevertheless, it was found that superconductivity has been found in 3d materials with magnetic transition-metal atoms and magnetic lattices as well.1 High-Tc cuprate superconductors, for example, were found to have exceedingly strong magnetic exchange,2 while Fe-based superconductors were found to have large Fe moments of several Bohr magnetons.3,4 Also of interest here are the binary vanadium compounds, such as V3Al, which belong to a class of simple superconductors with an A15 (β-W) crystal structure.5–8 Interestingly, V3Al has also been synthesized in a non-superconducting D03 Heusler phase with antiferromagnetic (AFM) order.9 This D03 phase of V3Al was predicted to be a gapless semiconductor10,11 and found experimentally9 to be a G-type antiferromagnet having a Néel temperature of TN=  600 K. It is clear that V3Z-type compounds represent a class of hybrid materials that could possess both superconducting and magnetic properties at the same temperature, which could provide potential next-generation platforms for hosting Majorana modes12 for applications in possible fault-tolerant quantum computer hosting and other quantum technology applications.Another well-known binary compound in the vanadium family is V3Ga, which has been used in superconducting applications for many years.13 The remarkable low-temperature elastic, electric, magnetic, and superconducting properties of this material have been investigated extensively both experimentally and theoretically (see, e.g., Refs. 14–20). The critical temperature of superconducting V3Ga in the A15 phase is 15 K.V3Ga can exist in two near-equilibrium phases, the A15 superconducting phase and the AFM D03 phase— an interesting and potentially useful result of their similar formation energies. Since the arrangement of atoms in binary V3Ga can accommodate both D03 and A15 structures (Fig. 1), one must study the stability of these two phases using density functional theory (DFT). DFT was used here to compute the formation energies for various crystalline and magnetic structures. Previous calculations for the D03 structure of V3Ga by Galanakis et al.11 predict a Heusler G-type AFM phase with a Néel temperature well above room temperature, which makes the compound attractive for spintronic applications.9,21,22 A recent study reported on an AFM phase of V3Ga in the β-W structure.23 The present magnetization measurements on bulk samples show a clear AFM behavior, in addition to a strong Meissner effect, indicating the presence of a superconducting transition temperature of 15 K