Intercalation of C70 with europium affords two kinds of magnetic compounds, a canted antiferromagnet EuxC70 (X ≈ 3) and a ferromagnet ExC70 (x ≈ 9) with transition temperatures (Tc) of 5 and 38 K, respectively. The Curie constants in the paramagnetic phase and the saturation moment in the ferromagnetic phase are both understood by the full moment of Eu2+ for both systems. The structure of Eu3-δC70 (δ ≈ 0.27) is pseudo-monoclinic, derived by a simple deformation of the parent face-centered cubic (fcc) structure. Eu9-δC70 (δ ≈ 0.2) forms an fcc structure, in which cuboctahedral clustering of Eu2+ ions is observed in the enhanced size octahedral holes. The observed Tc of the Eu9-δC70 ferromagnet is comparable to or larger than those of simple binary Eu-based ferromagnets, such as Eu chalcogenides or carbides, despite the low atomic ratio of Eu in the chemical formulas. This can be understood by the short Eu2+-Eu2+ distances and high coordination numbers permitted by the multiple occupation by Eu2+ ions of the expanded octahedral interstitial sites in higher fullerene-based solids.
ASJC Scopus subject areas
- Colloid and Surface Chemistry