Low-dimensional organic conductors show a rich phase diagram, which has, despite all efforts, still some unexplored regions. Charge ordered phases present in many compounds of the $${\hbox {(TMTTF)}}_2X$$ family are typically studied with their unique electronic properties in mind. An influence on the spin arrangement is, however, not expected at first glance. Here, we report temperature and angle dependent electron spin resonance (ESR) measurements on the quasi one-dimensional organic conductor $${\hbox {(TMTTF)}}_2 {\hbox {NO}}_3$$ . We found that the $${\hbox {(TMTTF)}}_2 {\hbox {NO}}_3$$ compound develops a peculiar anisotropy with a doubled periodicity ( $$ab'$$ -plane) of the ESR linewidth below about $$T_{\text {CO}}= ({250\pm 10})~\hbox {K}$$ . This behavior is similar to observations in the related compounds $${\hbox {(TMTTF)}}_2X$$ ( $$X = {\hbox {PF}}_6$$ , $${\hbox {SbF}}_6$$ and $${\hbox {AsF}}_6$$ ), where it has been attributed to relaxation processes of magnetically inequivalent sites in the charge-ordered state. For the structural analogous $${\hbox {(TMTTF)}}_2 {\hbox {ClO}}_4$$ , known for the absence of charge order, such angular dependence of the ESR signal is not observed. Therefore, our ESR measurements lead us to conclude that a charge-order phase is stabilized in the title compound below $$T_{\text {CO}} \approx 250~\hbox {K}$$ .

中文翻译：

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准一维有机导体中的电荷序相变 $${\hbox {(TMTTF)}}_2 {\hbox {NO}}_3$$

低维有机导体显示出丰富的相图，尽管付出了很多努力，但仍有一些未探索的区域。$${\hbox {(TMTTF)}}_2X$$ 家族的许多化合物中存在的电荷有序相通常在研究时考虑到它们独特的电子特性。然而，乍一看不会对自旋排列产生影响。在这里，我们报告了准一维有机导体 $${\hbox {(TMTTF)}}_2 {\hbox {NO}}_3$$ 的温度和角度相关电子自旋共振 (ESR) 测量值。我们发现 $${\hbox {(TMTTF)}}_2 {\hbox {NO}}_3$$ 化合物发展出一种特殊的各向异性，其 ESR 线宽的两倍周期性（ $$ab'$$ -plane）低于大约 $$T_{\text {CO}}= ({250\pm 10})~\hbox {K}$$ 。这种行为类似于在相关化合物 $${\hbox {(TMTTF)}}_2X$$ ( $$X = {\hbox {PF}}_6$$ , $${\hbox {SbF}}_6 $$ 和 $${\hbox {AsF}}_6$$ ），这归因于电荷有序状态下磁不等价位点的弛豫过程。对于结构类似的 $${\hbox {(TMTTF)}}_2 {\hbox {ClO}}_4$$ ，以没有电荷顺序而闻名，没有观察到 ESR 信号的这种角度依赖性。因此，我们的 ESR 测量使我们得出结论，在 $$T_{\text {CO}} \approx 250~\hbox {K}$$ 以下的标题化合物中，电荷有序相稳定。对于结构类似的 $${\hbox {(TMTTF)}}_2 {\hbox {ClO}}_4$$ ，以没有电荷顺序而闻名，没有观察到 ESR 信号的这种角度依赖性。因此，我们的 ESR 测量使我们得出结论，在 $$T_{\text {CO}} \approx 250~\hbox {K}$$ 以下的标题化合物中，电荷有序相稳定。对于结构类似的 $${\hbox {(TMTTF)}}_2 {\hbox {ClO}}_4$$ ，以没有电荷顺序而闻名，没有观察到 ESR 信号的这种角度依赖性。因此，我们的 ESR 测量使我们得出结论，在 $$T_{\text {CO}} \approx 250~\hbox {K}$$ 以下的标题化合物中，电荷有序相稳定。