Synthesis and characterisation of a novel europium-based graphite intercalation compound

In the lithium–europium–graphite system, a novel ternary compound was synthesised by direct immersion of a pyrolytic graphite platelet in a molten lithium-based alloy with a well chosen Li/Eu ratio at 400 °C. The ternary compound exhibits poly-layered intercalated sheets mainly constituted of two europium planes. Its chemical formula can be written LixEuC4, since the amount of lithium is still not determined. The 151Eu Mössbauer spectra clearly indicate a +II valence for europium. The magnetic susceptibility and the magnetisation versus temperature reveal a complex behaviour which is qualitatively described thanks to structural hypothesis and analogies with the magnetic properties of the binary EuC6 compound. A first ferromagnetic transition occurring at 225 K is attributed to interactions between both intercalated europium planes. The lower temperature susceptibility behaviour can be interpreted by antiferromagnetic interactions between in-plane neighbours and ferromagnetic interactions along the c-axis.