Spin frustration,charge ordering,and enhanced antiferromagnetism in TMTTF2SbF6

We theoretically investigate the effects of charge order and spin frustration on the spin ordering in TMTTF salts. Using first-principles band calculations, we find that a diagonal inter-chain transfer integral t_q1, which causes spin frustration between the inter-chain dimers in the dimer-Mott insulating state, strongly depends on the choice of anion. Within the numerical Lanczos exact diagonalization method, we show that the ferroelectric charge order changes the role of t_q1 from the spin frustration to the enhancement of the two-dimensionality in spin sector. The results indicate that t_q1 assists the cooperative behavior between charge order and antiferromagnetic state observed in TMTTF₂SbF₆.