The effect of Cr-substitution on the structural, electronic and magnetic properties of rutile VO2

Abstract

The effect of Cr-substitution on the structural, electronic and magnetic properties of rutile VO2 is investigated in this study. Pure VO2 is found to be a nonmagnetic metal, whereas all three Cr- substituted compounds [V1-xCrxO2 (VCO) with x = 0.25, 0.5, 0.75] are found to exhibit ferrimagnetic metallic behaviour. However, pure and all VCO compounds encounter metal to half-metal transition for the application of U = 2 eV, showing ferromagnetism. VO2, the VCO compounds V0.75Cr0.25O2 and V0.5Cr0.5O2 undergo metal–insulator transition (MIT) for U = 5 eV, 5.5 eV and 3.5 eV respectively, preserving ferromagnetism. Besides, V0.25Cr0.75O2 preserves its ferromagnetic half-metallic character even application of U as high as 6 eV. The breaking of mirror symmetries in the VO6/CrO6 octahedra induces structural distortions in all three VCO compounds. The MIT in pure VO2 is caused by the transfer of electrons from the V-dyz and dxz states to the dx2- y2 states. The simultaneous effect of structural distortion, V4+- V4+ and Cr3+-V5+ charge ordering and U is responsible for the MIT in V0.75Cr0.25O2. On the other hand, the simulteneous effect of structural distortion, transfer of electrons from V-t2g to Cr-t2g states and U is responsible for the MIT in V0.5Cr0.5O2. Although electron transfer is commenced from V-t2g to Cr-t2g states in V0.25Cr0.75O2, the latter cannot be completely occupied by the transferred electrons, resulting in the non-opening of a band gap near the Fermi level. The p-d hybridization between O-2p and V-3d/Cr-3d states, and V/Cr-O antiferromagnetic coupling facilitates ferromagnetism in insulating VO2, V0.75Cr0.25O2, V0.5Cr0.5O2 and half-metallic V0.25Cr0.75O2.