ABSTRACT

First-principles electronic structure calculations were employed for the electronic, magnetic and structural properties of rutile CrO₂. This material is a ferromagnetic half-metal with a semiconducting gap of 1.85 eV. The sharing of a single electron by Cr-3d_yz and d_xz orbitals is responsible for the metallic behaviour of CrO₂ for the majority spin channel. For the application of on-site Coulomb interaction U up to 4 eV, the electrons in the valence band polarise towards the Fermi level (E_F), while the electrons in the conduction band polarise away from E_F. The enhanced shifting of conduction bands of the spin minority channel is responsible for the augmentation of the semiconducting spin gap. This system undergoes a metal-insulator transition (MIT) upon the application of U = 5 eV. Due to the presence of electron correlation, the electron in the d_xy orbital shifts well below E_F, while bonding components of d_yz and d_xz orbitals are occupied by the remaining single electron. Nevertheless, anti-bonding components of these two states remain unoccupied. Consequently, a band gap of Eg ~ 0.2 eV is opened near E_F. The double exchange interactions between the partially occupied Cr-t_2g states and p-d hybridisations are responsible for the ferromagnetic behaviour of CrO₂ in both halfmetallic and insulating phases.

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