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We present computational results on electronic, magnetic, and structural properties of CoVMnSb, a quaternary Heusler alloy. Our calculations indicate that this material may crystallize in two energetically close structural phases: inverted and regular cubic. The inverted cubic phase is the ground state, with ferrimagnetic alignment, and around 80% spin polarization. Despite having a relatively large bandgap in the minority-spin channel close to the Fermi level, this phase does not undergo a half-metallic transition under pressure. This is explained by the “pinning” of the Fermi level at the minority-spin states at the Γ point. At the same time, the regular cubic phase is half-metallic and retains its perfect spin polarization under a wide range of mechanical strain. Transition to a regular cubic phase may be attained by applying uniform pressure (but not biaxial strain). In practice, this pressure may be realized by an atomic substitution of non-magnetic atoms (Sb) with another non-magnetic atom (Si) of a smaller radius. Our calculations indicate that 25% substitution of Sb with Si results in a half-metallic regular cubic phase being the ground state. In addition, CoVMnSb0.5Si0.5 retains its half-metallic properties under a considerable range of mechanical pressure, as well as exhibits thermodynamic stability, thus making this alloy attractive for potential spintronic applications. We hope that the presented results will stimulate experimental efforts to synthesize this compound. 

Half-metallic Heusler alloys have attracted significant attention due to their potential application in spin-transport-based devices. We have synthesized one such alloy, CoFeV 0.5 Mn 0.5 Si, using arc melting and high-vacuum annealing at 600 °C for 24 hours. First principles calculation indicates that CoFeV 0.5 Mn 0.5 Si shows a nearly half-metallic band structure with a degree of spin polarization of about 93%. In addition, this value can be enhanced by the application of tensile strain. The room temperature x-ray diffraction patterns are indexed with the cubic crystal structure without secondary phases. The annealed sample shows ferromagnetic order with the Curie temperature well above room temperature ( T c = 657 K) and a saturation magnetization of about 92 emu/g. Our results indicate that CoFeV 0.5 Mn 0.5 Si has a potential for room temperature spin-transport-based devices.