Transport properties of stage-1 graphite intercalation compounds

Abstract

Stage-1 Cu c Co 1−c Cl 2 graphite intercalation compounds approximate quasi-twodimensional (2D) random spin systems with competing ferromagnetic and antiferromagnetic intraplanar exchange interactions. The temperature dependence of the in-plane electrical resistivity of these compounds has been measured near critical temperatures. The magnetic resistivity ζ mag consists of the long-range spin-order part ζ LS and the spin-fluctuation part ζ SF . For 0 c 0.2 the long-range spin-order part ζ LS is dominant: the temperature dependence of ζ LS is described by a smeared power law with an exponent 2β, where β is the critical exponent of staggered magnetization. For 0.3 c 0.4 the spin-fluctuation part ζ SF becomes larger than ζ LS . For 0.5 c 0.95 no appreciable magnetic resistivity is observed. For c = 1 the derivative −dζ mag /dT shows a small peak at around 67 K due to the growth of short-range spin order which is characteristic of the 2D Heisenberg antiferromagnet. The critical behaviour of the in-plane resistivity can be explained in terms of a model based on π -d exchange interactions between π-electrons in the graphite layers and magnetic spins in the intercalate layers. The πelectrons are scattered by spins of a virtual antiferromagnetic in-plane spin configuration arising from the superposition of two ferromagnetic in-plane structures with spin directions antiparallel to each other. The π-d exchange interactions of these compounds are also discussed.

Transport properties of stage-1 magnetic random-mixture graphite intercalation compounds

“…This prediction seems to be inconsistent with a resistivity anomaly of the stage-2 CoCl 2 GIC near T c which has been reported by Yeh et al [2]: the magnetic contribution for the resistivity shows a small peak at T c . Note that similar behaviour is also observed for ζ versus T for the Ni c Mn 1−c Cl 2 GIC with c = 0.85 consisting of majority stage-2 with minority stage-1 and stage-3 GICs [31]. The resistivity ζ shows a kink-like behaviour at around 10 K, which is between T c = 9.58 K for c = 0.80 and 14.34 K for c = 0.90 derived from the ac magnetic susceptibility of stage-2 Ni c Mn 1−c Cl 2 GICs [32].…”