First-principles study of the interaction between paramagneticV4+centers through formally magnetically inactiveVO4tetrahedra in the quasi-one-dimensional spin systemsSr2V3O9andBa2V3O9

Abstract

We report a first-principles density-functional theory study of the origin of the magnetic properties of the quasi-one-dimensional spin systems ${\text{Sr}}_{2}{\text{V}}_{3}{\text{O}}_{9}$ and ${\text{Ba}}_{2}{\text{V}}_{3}{\text{O}}_{9}$. The calculated coupling constants are in very good agreement with experimental data and provide a basis to understand the correlation between structural features and magnetic coupling constants. In ${\text{Sr}}_{2}{\text{V}}_{3}{\text{O}}_{9}$, the predominant coupling is antiferromagnetic and is indeed mediated by one of the two different types of ${\text{VO}}_{4}$ tetrahedra. However, there is also a weaker ferromagnetic interaction along the direction of the octahedral chains, which is mediated by the corner-sharing oxygen atoms through a spin-polarization mechanism. The second type of tetrahedra apparently do not contribute to the magnetic coupling. In ${\text{Ba}}_{2}{\text{V}}_{3}{\text{O}}_{9}$, the antiferromagnetic coupling is dominated by a very substantial superexchange interaction of the vanadium ${d}_{xy}$ orbitals through the tetrahedra sharing only one oxygen atom with the octahedral chain. The second type of tetrahedra and the oxygen atoms nonshared with the tetrahedra provide ferromagnetic interactions which only partially counteract the antiferromagnetic superexchange coupling. Interchain disorder is predicted to have a very small influence on the coupling constants.