Magnetic resonance investigation for a possible antiferromagnetic subphase in (TMTTF)2Br

Abstract

To understand the electronic states on the boundary region between the commensurate antiferromagnetic (II) phase and the incommensurate spin-density-wave phase in the generalized phase diagram for one-dimensional organic conductors, we performed antiferromagnetic resonance (AFMR) and nuclear magnetic resonance (NMR) measurements for ${(\mathrm{TMTTF})}_{2}\mathrm{Br}$. The angular dependence of the AFMR fields at 1.5 K is different from that at 4.8 K, and the temperature dependence of the two AFMR modes is enhanced below 5 K. Furthermore, $^{2}\mathrm{D}$(Deuterium)-NMR measurements were performed for deuterated ${(\mathrm{TMTTF}\text{\ensuremath{-}}{d}_{12})}_{2}\mathrm{Br}$ to investigate charge distribution by quadrupole splitting at low temperatures. We found that the $^{2}\mathrm{D}$-NMR spectrum changes at 4 K in the antiferromagnetic phase. Successive phase transition and a possible magnetic structure are discussed.