# Nuclear Spin-Lattice Relaxation and EPR Studies of TTF-TCNQ and TMTTF-TCNQ Under Hydrostatic Pressure

C Berthier, J R Cooper, Denis Jerome, G Soda, C Weyl, J M Fabre, L Giral

► To cite this version:

C Berthier, J R Cooper, Denis Jerome, G Soda, C Weyl, et al., Nuclear Spin-Lattice Relaxation and EPR Studies of TTF-TCNQ and TMTTF-TCNQ Under Hydrostatic Pressure. Molecular Crystals and Liquid Crystals, 2015, 32, pp.267 - 270. 10.1080/15421407608083667. hal-05011651

HAL Id: hal-05011651

https://hal.science/hal-05011651v1

Submitted on 30 Mar 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

## Molecular Crystals and Liquid Crystals

Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/gmcl16

## Nuclear Spin-Lattice Relaxation and EPR Studies of TTF-TCNQ and TMTTF-TCNQ Under Hydrostatic Pressure

C. Berthier<sup>c</sup>, J. R. Cooper<sup>d</sup>, D. Jerome<sup>a</sup>, G. Soda<sup>e</sup>

, C. Weyl<sup>a</sup>, J. M. Fabre<sup>b</sup> & L. Giral<sup>b</sup>

<sup>a</sup> Laboratoire de Physique des Solides, Université Paris-Sud, 91405, Orsay, France

<sup>b</sup> Laboratoire de Chimie Organique Structurale, USTL, Place Eugène Bataillon, 34060, Montpellier, France

<sup>c</sup> Laboratoire de Spectrométrie Physique, USM Grenoble, BP 53, 38041, Grenoble Cedex, France

<sup>d</sup> Institute of Physics of the University, Zagreb, Yugoslavia

<sup>e</sup> Department of Chemistry, Faculty of Science, Osaka University, Osaka, Japan
Published online: 28 Mar 2007.

**To cite this article:** C. Berthier, J. R. Cooper, D. Jerome, G. Soda, C. Weyl, J. M. Fabre & L. Giral (1976) Nuclear Spin-Lattice Relaxation and EPR Studies of TTF-TCNQ and TMTTF-TCNQ Under Hydrostatic Pressure, Molecular Crystals and Liquid Crystals, 32:1, 267-270, DOI: 10.1080/15421407608083667

**To link to this article:** http://dx.doi.org/10.1080/15421407608083667
Taylor & Francis makes every effort to ensure the accuracy of all the information (the "Content") contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions
# Nuclear Spin-Lattice Relaxation and EPR Studies of TTF-TCNQ and TMTTF-TCNQ Under Hydrostatic Pressure†

C. BERTHIER,‡ J. R. COOPER,§ D. JEROME, G. SODA,‖ C. WEYL

Laboratoire de Physique des Solides,¶ Université Paris-Sud, 91405 Orsay, France

and

J. M. FABRE and L. GIRAL

Laboratoire de Chimie Organique Structurale, USTL, Place Eugène Bataillon, 34060 Montpellier, France

The quasi one-dimensional metallic character of TTF-TCNQ has been established by measurements of electrical conductivity, magnetic susceptibility, thermoelectric power, microwave conductivity and optical reflectivity at ambient pressure.¹ The metallic character of TMTTF-TCNQ is discussed in the preceding report² in comparison with that of TTF-TCNQ. The metallic state results from the strong π-orbital overlap along the TCNQ and TTF chains. In TTF-TCNQ both chains are metallic with transfer integrals of order 0.1 eV. The interchain transfer integral is of the order of 1 meV, which shows that the interchain hopping time of electrons is much shorter than the characteristic time scale of electron spin dynamics (ωs, Ts) and nuclear spin relaxation. Therefore, the ratio of the spin-lattice relaxation times of each chains observed by Rybaczewski et al.³ using deuterated TTF-TCNQ which is nearly independent of the temperature down to 60 K indicates a

<footnote>† Work supported in part by ATP Contract No. A 206.</footnote>

<footnote>‡ On leave from Laboratoire de Spectrométrie Physique, USM Grenoble, BP 53, 38041 Grenoble Cedex, France.</footnote>

<footnote>§ On leave from Institute of Physics of the University, Zagreb, Yugoslavia.</footnote>

<footnote>|| Visiting scientist on the scientific exchange Program between France and Japan, 1974-1975. On leave of absence from Department of Chemistry, Faculty of Science, Osaka University, Osaka, Japan.</footnote>

<footnote>¶ Laboratoire associé au CNRS.</footnote>
temperature independent ratio of the static susceptibilities of the individual chains. Under these conditions, the nuclear spin relaxation rate $T_1^{-1}$ should be related to the observed spin susceptibility $\chi_s$ by the Korringa relation, $(T_1 T)^{-1} \propto A^2 \chi_s^2 K(u, T)$, where K is the Korringa enhancement factor which depends on the electron-electron Coulomb correlation $u$ and temperature $T$.

Although Rybaczewski et al. have concluded that the Coulomb correlation is small [$K(u \cdot T) \simeq 1$] and $(T_1 T)^{-1} \propto \chi_s^2$ in TTF-TCNQ, as can be seen in Figure 1, the log-log plot of $(T_1 T)^{-1}$ against $\chi_s$ shows that the exponent of $\alpha$ in the relation $(T_1 T)^{-1} \propto \chi_s^\alpha$ is not exactly 2.0, but rather 2.2 for both materials, TTF-TCNQ and TMTTF-TCNQ.

The purpose of this pressure investigation is to clarify whether this "Korringa" behaviour is followed when a change of the density of states at Fermi level is induced by means other than a change in the temperature. The experimental procedures for the measurements of relaxation rate are the same as those mentioned in the preceding report.² The EPR measurements under pressure were also made at 40 MHz using a different spectrometer sensitive to the dispersive component of $\chi$. Although there is clear evidence for large increases in EPR linewidth under pressure the values of the susceptibility quoted here are subject to the following two limitations: (a) a detailed analysis of the lineshape needs to be carried out, especially for TTF-TCNQ where the linewidth is ~1/3 of the applied static field; (b) further checks on the sensitivity of the spectrometer under pressure should be made. The pressure equipment will be described elsewhere.

<figure><img src="image_3.png" /><figcaption>FIGURE 1 Log-log plots of $(T_1 T)^{-1}$ versus $\chi_s$
---■-- TMTTF-TCNQ ambient pressure, temperatures from 100-350 K
--- TTF-TCNQ ambient pressure, temperatures from 100-300 K (Refs. 3 and 4)
-●- TMTTF-TCNQ room temperature, pressures up to 10 Kbar
-○- TTF-TCNQ room temperature, pressures up to 4 Kbar.</figcaption></figure>
<figure><img src="image_4.png" /><figcaption>FIGURE 2 EPR results for TMTTF-TCNQ at room temperature</figcaption></figure>

○ Left-hand scale—linewidth *L* versus pressure

● Right-hand scale—normalized spin susceptibility (*L*²*H* of derived dispersion curves) versus pressure.

Experimental results are summarized as follows.

1) Pressure variation of EPR line-width and spin susceptibility were measured up to 10 Kbar for TMTTF-TCNQ and up to 4 Kbar for TTF-TCNQ. In the latter case the linewidth is so broad that it becomes comparable to the applied static field. In both cases, the linewidth increases approximately linearly with pressure, 0.48 gauss/Kbar (i.e. 18%/Kbar) for TMTTF-TCNQ (Figure 2) and 1.4 gauss/Kbar (i.e. 28%/Kbar) for TTF-TCNQ (Figure 3) at room temperature. It is interesting to note the relative changes in the line-width of TTF-TCNQ under pressure are independent of temperature in the range studied.

<figure><img src="image_5.png" /><figcaption>FIGURE 3 EPR results for TTF-TCNQ at several temperatures. (a) Linewidth *L* versus pressure at 343 K ●, 295 K ■, 220 K ○ and 170 K ▲. (b) Normalized spin susceptibility (*L*²*H* of derived dispersion curves) versus pressure at 343 K △, 295 K ◆, 220 K ▲, 170 K ○. The values of *L*²*H* are normalized by the ambient pressure values at each temperature.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>FIGURE 4 Pressure dependence of proton relaxation rate at room temperature, ● TTF-TCNQ, ■ TMTTF-TCNQ.</figcaption></figure>

2) In both materials, $\chi_s$ decreases with pressure. The relative decreases under pressure are 5.6%/Kbar for TMTTF-TCNQ and 7% Kbar for TTF-TCNQ at room temperature (Figures 2 and 3b).

3) As shown in Figure 4, the nuclear relaxation rate decreases strongly with pressure in both materials rather more quickly than expected from the pressure variation of $\chi_s$. In Figure 1 the relaxation rates are also plotted against $\chi_s$ with pressure as the implicit parameter. This shows that there is also some deviation from a Korringa law, the exponents are $\approx 2.2$ for both materials, which is the same as the value derived from the temperature variation. It is easily concluded that the electronic states of both quasi one-dimensional systems resemble each other. The nuclear spin relaxation rate is therefore related to the observed spin susceptibility by the phenomenological equation, $T_1^{-1} \propto A^2 T \chi_s^{2.2}$. The difference of the exponent from 2.0 may be due to the interchain interaction and to the electron correlation. This point needs deeper and more precise consideration.

4) The temperature variation of relaxation rate under pressure shows that at 10 Kbar the maximum of $T_1^{-1}$ due to CH$_3$ rotation moves to 70 K and the hindering potential increases to twice the value at ambient pressure. But the EPR and NMR results up to 10 Kbar mentioned above make it clear that the dynamical disorder of CH$_3$ rotation has no effect on the electronic states above 80 K.

1. See the recent review article by A. J. Heeger and A. F. Garito in *Low-Dimensional Cooperative Phenomena* (Ed. by H. J. Keller, Plenum Press, 1975), pp. 89, and references therein.

2. C. Berthier *et al.*, this conference, previous communication.

3. E. F. Rybaczewski, A. F. Garito, and A. J. Heeger, *Phys. Rev. Letters*, **34**, 524 (1975).

4. J. C. Scott, A. F. Garito, and A. J. Heeger, *Phys. Rev.*, **B10**, 3131 (1974).