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

Abstract

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_x²_{- y}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 [${\epsilon }_1\left(\omega \right)$] and imaginary [${\epsilon }_2\left(\omega \right)$] 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 $L\left(\omega \right)$ 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.