13C NMR study of commensurate antiferromagnetism in (TMTTF)2Br

Abstract

Quasi-one-dimensional organic conductors (TMTCF) 2 X have various electric and magnetic properties. Although theoretical and experimental studies have suggested that (TMTTF) 2 Br has the properties of commensurate antiferromagnetism, details of the magnetic structure of this compound are unclear. Two types of antiferromagnetism are expected, one due to a localized electron and the other to the nesting of the Fermi surface. We therefore assessed the antiferromagnetic structure of (TMTTF) 2 Br using 13 C NMR. Site assignment of the observed antiferromagnetic spectrum confirmed that there were two magnetic molecular sites, with staggered moments and amplitude of 0.11μ B /molecule, as well as nonmagnetic molecular sites. A commensurate structure with antiferromagnetic ordering of (↑ • ↓ •) along a one-dimensional chain would be expected as the freezing of antiferromagnetic fluctuations in the charge-ordered phase of the (TMTTF) 2 AsF 6 salt. The presence of a nodal site is strongly suggestive of the nesting type antiferromagnetism. The fine structure of the antiferromagnetic spectrum suggests superlattice along the interchain direction. We could not observe line broadening due to the charge order above the antiferromagnetic transition.

Spin-density wave in the vicinity of superconducting state in λ−(BETS)2GaBrxCl4−x probed by Kobayashi1, Ishikawa2, Ohnuma3 et al. 2020Phys. Rev. Research9060View full textAdd to dashboardCite

“…The present NMR results of diverging in 1/T 1 T and the existence of several discrete NMR peaks, including the center peak with small internal field, were similarly observed in the 13 C NMR study of (TMTTF) 2 Br [31,32], which undergoes [26]. (1/T 1 T ) kink , ρ min , ρ max , χ , and T c are defined by the temperatures exhibiting the 1/T 1 T maximum, metal-insulator transition, broad resistivity maximum, considerable decrease in spin susceptibility, and SC transition, respectively.…”

“…In λ-(BETS) 2 GaBr 0.75 Cl 3.25 , although the precise magnetic structure cannot be determined due to limited spectral resolution, the spectral shape was observed to be close to that expected in the commensurate SDW. In addition, 1/T 1 of (TMTTF) 2 Br demonstrated temperature dependence of the thermal activation type in the commensurate SDW state [31,32], whereas 1/T 1 of (TMTSF) 2 PF 6 followed the power-law behavior below the transition to the incommensurate SDW state [35]. The drastic decrease in 1/T 1 T below 13 K in λ-(BETS) 2 GaBr 0.75 Cl 3.25 is similar to the behavior of (TMTTF) 2 Br, suggesting that λ-(BETS) 2 GaBr 0.75 Cl 3.25 exhibits the commensurate SDW state.…”

Spin density wave in the strongly dimerized quasi-one-dimensional organic conductor (DMET-TTF) 2AuBr2

“…The AFM state of the dimer Mott insulator with 2:1 stoichiometry has the amplitude of the magnetic moment as m = 1μ B /dimer. The dimer Mott insulators β -(BEDT-TTF) 2 ICl 2 [30,31] and (TMTTF) 2 SbF 6 [5,32] at ambient pressure show 1μ B /dimer in the AFM phase. However, C-SDW and IC-SDW phases TMTCF families have a small amplitude the magnetic moment.…”

“…We can obtain a(θ, φ) as a slope of the linear function and σ (θ, φ) as an intercept. A and σ are evaluated from a set of a(θ, φ) and σ (θ, φ), The elements of hyperfine coupling and the chemical shift tensor are semiquantitatively similar to (TMTTF) 2 Br [5] and (TMTSF) 2 PF 6 [33].…”

“…(TMTTF) 2 Br is located at a lower-pressure region than (TMTSF) 2 PF 6 in the generalized phase diagram of (TMTCF) 2 X [2]. The ground state in (TMTTF) 2 Br has been reported as commensurate SDW (C-SDW) [3] with a (↑ • ↓ •) type magnetic structure [4,5]. To investigate the role of the dimensionality, electronic correlation, and dimerization of the donor in the Q1D system, we focus on the us-DMET-STF [dimethyl(ethylenedithio)diselenadithiafulvalene, abbreviated as DMET-STF hereafter] where "us" denotes the molecule's unsymmetrical shape due to the positioning of Se atoms as shown in Fig.…”