A comprehensive first-principles investigation of the structure, electronic, magnetic and optical properties of orthorhombic CrO2 at 14 GPa

The structure, electronic, magnetic and optical properties of orthorhombic CrO2 (o-CrO2) at 14 GPa are extensively investigated from the first-principles calculations. It is revealed that the Cr-O distances and <O-Cr-O angles in o-CrO2 decrease compared to rutile CrO2 (r-CrO2), resulting in structural distortion in the CrO6 octahedra. The system is half-metallic in both GGA and GGA + U (U is the Coulomb interaction) calculations with metallic/insulating up/down spin channel. The partial filling and delocalization of electrons in the Cr-3d(x)(- y)(2)(2) and O-2p(x/y) state near the Fermi level results in the metallic behaviour of o-CrO2 for the up spin channel. The ground state energy calculations confirm that ferromagnetism is stabilized in o-CrO2, with the strength of ferromagnetism enhanced upon the application of U = 3 eV. The cooperative effect of p-d hybridization and Cr-O antiferromagnetic coupling results in the ferromagnetism in o-CrO2. The Curie temperature (T-c) of o-CrO2 reduces by 166 K compared to r-CrO2 and T-c reaches towards the room temperature for U = 3 eV. Several peaks are observed both for the real [epsilon(1)(omega)] and imaginary [epsilon(2)(omega)] parts of the dielectric function, resulting in anisotropy in the structure. The anisotropy in the structure reduces upon the application of U = 3 eV. The net electron loss function L(omega) is augmented upon the application of U, resulting in the reduction of conductivity of o-CrO2. More interestingly, the plasmon frequencies corresponding to the x, y and z components of L(omega) decrease upon the application of U.