High stage graphite intercalation compounds of rare earth metals and alkali-metal vapor-transport technique

Abstract

We present a new technique to synthesize high stage graphite intercalation compounds of low vapor-pressure elements such as rare earth metals (RE). The technique consists of two processes, (1) the co-intercalation of alkali-metal (AM) and RE, in which the stage is mainly controlled by vapor pressure of AM, and (2) the following de-intercalation of AM from the compound, in which the preferential removal of AM results in a high stage RE_GIC. We first obtained stages 2, 3 and 4 Eu- and stage 2 Sm-GICs. However an intercalant layer is composed of a mixture of RE and residual AM; i.e. the in-plane composition x in Eu xK 1−x-GIC was less than 0.75. The temperature dependence of magnetization of stage 3 Eu 0.75K 0.25-GIC shows two anomalies at T c1 = 30 K and T c2 = 80 K. While at T > T c2 it obeys the Curie-Weiss law with ⊗ = −15K, the magnetization process at T < T c1 shows remarkable metamagnetism which resembles that of stage 1 EuC 6. The magnetic anomaly at T c2 is unique to high stage Eu compounds.