Possible half-metallic and spin-gapless semiconducting behavior in quaternary Heusler compounds Co_2-xY_xFeGa/Al (Y = Ti, V, Cr, Mn, Fe, and Co, x = 0.50)

The realization of physical systems whose electronic and magnetic properties can be easily manipulated by playing with valence electrons are very promising from both the fundamental and applied perspectives. Half-metallic ferromagnets are ideal candidates for spintronic applications because of their high spin polarization of charge carriers at the Fermi level. Spin-gapless semiconductors can be regarded as a combination of gapless semiconductors and half-metallic ferromagnets where the conducting electrons or holes are not only 100% spin polarized but also easily excited. The realization of spin-gapless semiconducting behavior in Heusler alloys is expected to fulfill the needs for semiconductor spintronics.  In this work, we have introduced the substitution of all low valence transition metals atoms Y = Ti, V, Cr, Mn, and Fe to Co atoms in the parent Co₂FeGa/Al system, and examined the structural, electronic, magnetic, electron transport and mechanical properties of quaternary Heusler compounds Co_2-xY_xFeGa/Al (x = 0.50), both experimentally and theoretically to get a global overview of the electronic, magnetic, electron transport and mechanical properties, promising candidates for spintronics applications. All single-phase alloys exhibit cubic crystal structure with a strong tendency towards L2₁ ordering. The low-temperature saturation magnetic moments agree fairly well with the values expected from a Slater-Pauling rule for half metals. The temperature dependence of electrical resistivity for Mn substituted alloys show tunable spin-gapless semiconducting behavior in the complete temperature regime (5K-400K). Ab initio calculations are also performed to understand the experimental findings.