First-Principle Analysis of K₂NaTiX6 (X=F, Cl and Br): Magnetic Stability and Half-Metallic Behavior

This study presents a detailed density functional theory (DFT) analysis of the double perovskite compounds K 2 NaTiX 6 (X = F, Cl, Br). Our findings indicate that these materials are thermodynamically stable and exhibit intriguing electronic and magnetic properties. All three compounds show ferromagnetic ordering and half-metallic behavior, characterized by a spin gap in the minority spin channel. Notably, the half-metallic gap increases from F to Cl to Br, suggesting that the electronic structure can be tuned through halide substitution. The magnetic properties are largely attributed to the titanium (Ti) atom, which contributes a consistent magnetic moment of 1 μB per formula unit. To account for strong electron correlations, we applied the Hubbard U correction to the Ti d-orbitals, varying U from 1 to 4 eV. This correction led to an increase in both the half-metallic gap and the local magnetic moment on Ti, while preserving the total magnetic moment. Using the Heisenberg model, we estimated the Curie temperatures based on calculated exchange constants, providing insights into the thermal stability of the magnetic ordering. K 2 NaTiX₆ compounds are promising for spintronic applications due to their complete spin polarization at the Fermi level, supported by numerous studies on ferromagnetic half-metal halides.