Bond-length-driven magnetic transition in quasi-one-dimensional CrSbX3(X= S, Se).

Usingab initiocalculations, we investigate the magnetic ground states of quasi-one-dimensional insulating CrSb(= S, Se) with infinite double-rutile chains. Within conventional band theory, without explicit Coulomb correlations (), we obtain band gaps in close agreement with experiment. Remarkably, we find that the magnetic order is highly sensitive to the Cr-Cr bond length: increasing the bond length induces a transition from antiferromagnetic to ferromagnetic order at a critical distanceÅ. Accordingly,lies near the transition boundary, whereasis robustly ferromagnetic, in good agreement with experiment. Analysis of the exchange interactions reveals that the first-order phase transition is dominated by a sign reversal of the intrachain nearest-neighbor superexchangemediated by chalcogen ions, while the intrachain direct exchangeremains ferromagnetic and changes only gradually. This behavior reflects an emergent Bethe-Slater-like behavior driven by competing exchange pathways in a quasi-1D transition-metal system, where the competition betweenanddictates the magnetic ground state. Besides, the electronic structures of the ground states of each compound are investigated.