Charge ordering in the metal-insulator transition of V-doped CrO₂ in the rutile structure

Electronic, magnetic, and structural properties of pure and V-doped CrO₂ were extensively investigated utilizing density functional theory. Usually, pure CrO₂ is a half-metallic ferromagnet with conductive spin majority species and insulating spin minority species. This system remains in its half-metallic ferromagnetic phase even at 50% V-substitution for Cr within the crystal. The V-substituted compound Cr_0.5V_0.5O₂ encounters metal-insulator transition upon the application of on-site Coulomb repulsion U = 7 eV preserving its ferromagnetism in the insulating phase. It is revealed in this study that Cr³⁺-V⁵⁺ charge ordering accompanied by the transfer of the single V-3d electron to the Cr-3dt_2g orbitals triggers metal-insulator transition in Cr_0.5V_0.5O₂. The ferromagnetism of Cr_0.5V_0.5O₂ in the insulating phase arises predominantly due to strong Hund's coupling between the occupied electrons in the Cr-t_2g states. Besides this, the ferromagnetic Curie temperature (T_c) decreases significantly due to V-substitution. Interestingly, a structural distortion is observed due to tilting of CrO₆ or VO₆ octahedra across the metal-insulator transition of Cr_0.5V_0.5O₂. Graphical abstract The V-doped compound Cr_0.5V_0.5O₂ is found a half-metallic ferromagnet (HMF) in the absence of on-site Coulomb interaction (U). This HMF behavor maintains up to U = 6 eV. Eventually, this system encounters metal-insulator transition (MIT) upon the application of U = 7 eV with a band gap of E_g ~ 0.31 eV. Nevertheless, applications of higher U widen the band gaps. In this figure, calculated total (black), Cr-3d (red), V-3d (violet), and O-2p (blue) DOS of Cr_0.5V_0.5O₂ for U = 8 eV are illustrated. The system is insulating with a band gap of E_g ~ 0.7 eV.