Role of V–V dimerization on electronic and magnetic properties of ilmenite-type CoVO3

Abstract

Abstract Structural, electronic and magnetic properties of ilmenite-type CoVO3 have been explored via the generalized gradient approximation + effective Hubbard U eff correction, in the framework of density functional theory. Our results indicate that high temperature rhombohedral R 3 ˉ phase is metallic with oxidation states and electronic configurations Co2+ ( t 2 g ↑ 3 e g ↑ 2 t 2 g ↓ 2 e g ↓ 0 ), V4+ ( t 2 g ↑ 1 e g ↑ 0 t 2 g ↓ 0 e g ↓ 0 ), respectively, while low temperature triclinic P 1 ˉ phase, induced from spin-Peierls transition in the V–V dimerization manner, is insulating, maintaining charge and electronic states unchanged. Furthermore, the A-type antiferromagnetic ordering, where the ferromagnetic honeycomb layers are anti-aligned along the stacking axis, is identified to be the magnetic ground state for the low temperature phase, in nice agreement with experimental findings, analogous to CoTiO3. The unexpected intralayer ferromagnetic couplings can be attributed to the intraorbital t2g −t2g exchange coupling, which was assumed to be small earlier and ignored, but actually large in honeycomb cobaltates with 3d 7 electronic configuration. In addition, the computed magnetic moment on Co2+ ion ranges from 2.5 to 2.7 μ B, Hubbard U eff dependent, close to ideal S = 3/2 state, rather than the anticipated J eff = 1/2 state. Furthermore, the supplemental calculations, taking spin-orbit coupling (SOC) into account, uncover faint orbital moments of 0.21–0.27 μ B at the Co site, illustrating the insignificance of SOC. Except for the inevitable trigonal distortions, the excessive structural distortion triggered by the formation V–V dimerization, i.e. the breaking of trigonal symmetry around Co2+, further lifts the degeneracy of t 2g orbitals and increases crystal field splitting, driving it away from potential candidates for realizing Kitaev model physics.