Beyond conventional half-metals: gapless states and spin gapless semiconducting behavior in X<sub>2</sub>MnGa (X =Ti, Ir) Heusler compounds

The search for high-performance spintronic materials motivates the exploration of Heusler alloys with unconventional electronic properties. Using density functional theory with Hubbard correction (DFT+U, U = 4 eV), we investigate X2MnGa (X = Ti, Ir) alloys, which stabilize in the ferromagnetic L21-type structure with strong thermodynamic stability. Electronic structure calculations reveal contrasting behaviors: Ti2MnGa transitions from a metallic L21-type phase to a spin gapless semiconductor (SGS) in the XA-type, while Ir2MnGa exhibits gapless half-metallicity behavior in the L21-type but becomes half-metallic in the XA-type. The magnetic properties are governed by spd hybridization between Mn-3d and X-d/Ga-p states, which stabilizes ferromagnetism and tailors electronic states near the Fermi level. The Hubbard U correction proves essential for accurately describing the correlated Mn-3d electrons. These alloys combine structural stability with tunable electronic and magnetic properties, offering a promising platform for spin-polarized transport in next-generation spintronic devices.