Formation, electronic, mechanical and magnetic properties of all-d-metal Heusler alloys Sc2NiCu, Sc2NiCo and Sc2CoCu

Sc2-based all-d-metal Heusler alloys Sc2NiCu, Sc2NiCo and Sc2CoCu were synthesized successfully. XRD measurement suggests that they are single phase and crystallize in the L21 structure or L21 with a degree of atomic disorder, agreeing with the theoretical results that L21 structure has much lower total energy than XA. The phonon dispersion curves of L21 alloys have no imaginary frequency in the whole Brillouin zone, but for XA type alloys, obvious imaginary frequency can be observed, making them less stable. First-principles calculations indicate non-magnetic ground state for these alloys. Accordingly, the magnetizations of them at 5 K are very small and no magnetic ordering transition can be observed in their thermomagnetic curves. Sc2NiCu and Sc2CoCu show a metallic character in the rho-T curves, while Sc2NiCo is semiconductor-like. The elastic constants are calculated and the results show that the three alloys are mechanically stable. The Pugh's ratio and Poisson's ratio are determined and indicate the ductile nature of them.