Ground states and the critical behavior in the quasi-one-dimensional complexes (TMTTF)2[(AsF6)x(SbF6)1-x]

C-13 NMR measurements were carried out to understand the chemical pressure effect on the ground state in quasi-one-dimensional (1D) organic complexes using the alloy system (TMTTF)(2)[(AsF6)(x)(SbF6)(1-x)] (x similar to 0.3, 0.5, 0.67). The temperature of the charge-ordering transition decreases with the concentration of AsF6. Additional line splitting and the rapid increase in the spin-lattice relaxation rate, 1/T-1, on cooling for the salt of x similar to 0.3 indicates that the ground state of the salt is antiferromagnetic. In the x similar to 0.67 alloy, the spin gap opens without antiferromagnetic spin correlations. The intermediate salt of x similar to 0.5 is located in the vicinity of the quantum critical region between two phases at low temperatures. The quasi-1D correlation and antiferromagnetic critical behavior are discussed in terms of the power-law behavior of 1/T-1.