J. Phys. I France
Volume 1, Numéro 4, April 1991
Page(s) 537 - 551
DOI: 10.1051/jp1:1991150
J. Phys. I France 1 (1991) 537-551

ESR in CrCl $\mathsf{_3}$-based graphite intercalation and bi-intercalation compounds

S. Chehab, P. Biensan, J. Amiell and S. Flandrois

Centre de Recherche Paul Pascal, C.N.R.S., Château Brivazac, 33600 Pessac, France

(Received 14 September 1990, revised 29 October 1990, accepted 13 December 1990)

ESR experiments have been performed on stage-1, -2, -3, CrCl 3 graphite intercalation compounds as well as on CrCl 3-CdCl 2 and CrCl 3-MnCl 2 graphite bi-intercalation compounds. The measurements have been carried out at the X-band frequency and over the temperature range $4.2~{\rm K}\leqslant T\leqslant 294~{\rm K}$. The variation of the linewidth $(\Delta H)$ and the resonance field $(H_{\rm r})$ have been examined as a function of the temperature and the angle $\theta$ between the external field and the crystal c-axis. The results reflect the anisotropic 2D character of these systems. The room temperature angular dependence of $\Delta H$ follows a $(3 \cos^{2} \theta-1)^{2}$-like behavior and that of $H_{\rm r}$ has a $(3 \cos^{2} \theta-1)$-like form. For the singly intercalated systems, $\Delta H$ decreases with T according to $(1-\Theta_{\rm cw}/T)$ in the high temperature region, then shows a local minimum at around 35 K followed by a critical-like divergence at lower temperatures. In the bi-intercalated compounds, $\Delta H$ vs. T exhibits three types of behavior : for $T\geqslant 220$ K, $\Delta H$ behaves like T2; for 120 K $\leqslant T\leqslant 220~{\rm K}$, $\Delta H$ seems to be proportional to $(1-\Theta_{\rm cw}/T)$; for $T\leqslant 120$ K, $\Delta H$ shows a gradual increase which becomes steeper and steeper with falling T. The T2-like behavior may be explained in connection to a spin-lattice relaxation phenomenon which becomes important at high temperatures. The temperature dependence of $H_{\rm r}$ is characterized by an increase of $H_{{\rm r}\parallel}$ and a decrease of $H_{{\rm r}\perp}$ with decreasing temperature. This is consistent with the theoretical predictions developed for anisotropic low-dimensional systems, reflecting the increase in the anisotropy of low temperature susceptibility.

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