Spin dynamics in theS=12antiferromagnetic chain compoundsδ−(

Abstract

We present a multifrequency electron spin resonance study in the range of 4-420 GHz of the quasi-onedimensional, nondimerized, quarter-filled Mott insulators, ␦-͑EDT-TTF-CONMe 2 ͒ 2 X ͑X =AsF 6 ,Br͒. In the high-temperature orthorhombic phase above T ϳ 190 K, the magnitude and the temperature dependence of the high-temperature spin susceptibility are described by a S = 1 2 Heisenberg antiferromagnetic chain with J AsF 6 = 298 K and J Br = 474 K coupling constants for X =AsF 6 and Br, respectively. We estimate from the temperature dependence of the linewidth ͑⌬H͒ an exchange anisotropy, JЈ / J of ϳ2 ϫ 10 −3 . The frequency dependence of ⌬H and the g shift have an unusual quadratic dependence in all crystallographic orientations that we attribute to an antisymmetric exchange ͑Dzyaloshinskii-Moriya͒ interaction.

Frustration-induced one-dimensionality in the isosceles triangular antiferromagnetic lattice of δ -(EDT-TTF- CONMe2)2AsF6

“…EDT 2 AsF 6 single crystals were grown using electrochemical oxidation of EDT like in earlier studies of the same compound [14][15][16][17] . ESR was performed by homebuilt spectrometers operating at 111.2 and 222.4 GHz frequencies [18][19][20] .…”

“…There is no direct measurement of J 2 ; we estimate it from the calculated overlap integrals along and perpendicular to the chains 14 to be about 30 K. Overlap is small in the c direction where AsF 6 ions separate the chains. The exchange parameters are somewhat modified below the orthorhombic to monoclinic transition 16 at 190 K. Anisotropies, deviations from the isotropic exchange Heisenberg model are weak 17 . An antiferromagnetic (AF) ordering has been observed 15 at T N = 8.5 K. The DM interaction between molecules along chains in the a direction is forbidden by symmetry 16 in the AF state and the first neighbor dipoledipole interaction is also canceled (see III E).…”

“…However, below 40 K, the 9 GHz ESR intensity decreases rapidly with decreasing temperature due to the decrease of the paramagnetic regions in the sample 14,17 . The static susceptibility remains large 14 , suggesting that below 40 K the material is inhomogeneous; it consists of paramagnetic and antiferromagnetically ordered regions.…”

“…On the other hand, the DM interaction is not zero between neighbor "a" chains in the (a,c) plane. A small, frequency dependent broadening of the ESR line has been attributed to the DM interaction between chains in the paramagnetic state 17 . A negligible ferrimagnetism is expected in the magnetically ordered regions, since the chains are antiferromagnetic with a large exchange, J in the ordered state.…”

Infrared and Raman spectroscopic studies of the charge localization in one‐dimensional organic metals (DMtTTF)2X (X = ReO4, ClO4) with regular organic stacks

“…[8,11,12] Recently, the quasi-1D quarter-filled Mott insulators with regular stacks [EDT-TTF-CONMe 2 ] 2 X (EDT-TTF-CONMe 2 = tertiary amide functionalized ethylenedithiotetrathiafulvalene; X = AsF 6 -, Br -) were intensively studied. [13][14][15][16][17] At ambient pressure, these salts show an insulating character, which is related to a stable charge-ordered state, and at low temperature, they undergo a transition to an antiferromagnetic state. On the basis of electrical transport and nuclear magnetic resonance measurements, a common pressure-temperature phase diagram was deduced for these two salts.…”