ESR in CrCl3-based graphite intercalation and bi-intercalation compounds

Abstract

ESR experiments have been performed on stage-1, -2, -3, CrCl3 graphite intercalation compounds as well as on CrCl3-CdCl2 and CrCl3-MnCl2 graphite bi-intercalation compounds. The measurements have been carried out at the X-band frequency and over the temperature range $4.2~{\rm K}\leq T\leq 294~{\rm K}$. The variation of the linewidth (ΔH) and the resonance field (Hr) have been examined as a function of the temperature and the angle θ 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 ΔH follows a (3 cos2 θ-1)2-like behavior and that of Hr has a (3 cos2 θ-1)-like form. For the singly intercalated systems, ΔH decreases with T according to (1-Θcw/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, ΔH vs. T exhibits three types of behavior : for T≥220 K, ΔH behaves like T2; for 120 K $\leq T\leq 220~{\rm K}$, ΔH seems to be proportional to (1-Θcw/T); for T≤120 K, ΔH 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 Hr is characterized by an increase of Hr∥ and a decrease of Hr⊥ 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.