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

Structural, electronic and magnetic properties of ilmenite-type CoVO₃have been explored via the generalized gradient approximation + effective HubbardU_effcorrection, in the framework of density functional theory. Our results indicate that high temperature rhombohedralR3-phase is metallic with oxidation states and electronic configurations Co²⁺(t2g↑3eg↑2t2g↓2eg↓0), V⁴⁺(t2g↑1eg↑0t2g↓0eg↓0), respectively, while low temperature triclinicP1-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 intraorbitalt_2g-t_2gexchange coupling, which was assumed to be small earlier and ignored, but actually large in honeycomb cobaltates with 3d⁷electronic configuration. In addition, the computed magnetic moment on Co²⁺ion ranges from 2.5 to 2.7μ_B, HubbardU_effdependent, close to idealS= 3/2 state, rather than the anticipatedJ_eff= 1/2 state. Furthermore, the supplemental calculations, taking spin-orbit coupling (SOC) into account, uncover faint orbital moments of 0.21-0.27μ_Bat 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 oft_2gorbitals and increases crystal field splitting, driving it away from potential candidates for realizing Kitaev model physics.