Synthesis, Structure, and Magnetic Properties of the Fullerene-Based Ferromagnets Eu₃C₇₀ and Eu₉C₇₀

Abstract

Intercalation of C(70) with europium affords two kinds of magnetic compounds, a canted antiferromagnet Eu(x)C(70) (x approximately 3) and a ferromagnet Eu(x)C(70) (x approximately 9) with transition temperatures (T(C)) 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 Eu(2+) for both systems. The structure of Eu(3)(-)(delta)C(70) (delta approximately 0.27) is pseudo-monoclinic, derived by a simple deformation of the parent face-centered cubic (fcc) structure. Eu(9)(-)(delta)C(70) (delta approximately 0.2) forms an fcc structure, in which cuboctahedral clustering of Eu(2+) ions is observed in the enhanced size octahedral holes. The observed T(C) of the Eu(9)(-)(delta)C(70) 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 Eu(2+)-Eu(2+) distances and high coordination numbers permitted by the multiple occupation by Eu(2+) ions of the expanded octahedral interstitial sites in higher fullerene-based solids.

Pressure-induced transformation in Na4C60polymer: X-ray diffraction and Raman scattering experiments

“…A similar reversibility of the pressure-induced polymerization has also been reported in other intercalated fullerides. 18,[38][39][40] From another point of view the covalent 3D network in such C 60 polymers, containing carbon cages, can be seen as carbon analogs of silicon clathrate compounds. Recently, the barium-containing silicon clathrate compound Ba 8 Si 46 , isotypic with the type-I gas (G) hydrate Gx-(H 2 O) 46 , has been proved to be a superconductor with a transition temperature (T c ) of 8.0 K. 41 It could, therefore, be speculated that the 3D Na 4 C 60 phase observed in our experiments might possess a structure similar to that of such compounds but composed of carbon instead of silicon.…”

Magnetism in polymerized fullerenes

“…Third, a key feature for obtaining a ferromagnetic phase is mutual orientation of adjacent fullerene molecules [14]. Similar situation occurs with fullerene-based solids having an antiferromagnetic ground state: the sign of magnetic interactions between C 60 anions depends on the relative orientation of neighboring molecules [15].…”

Doping a C60 molecule with potassium atoms: A theoretical study

“…[7][8][9] There are also doped fullerides that display ferromagnetism, antiferromagnetism, and giant magnetoresistance. [10][11][12] At the molecular level, a recent experiment by Yamachika et al has shown that a single C 60 molecule can be doped with individual potassium atoms. 13 In the experiment K atoms adsorbed on the Ag ͑001͒ surface can be attached to an isolated C 60 molecule by moving the molecule over them using a scanning tunneling microscope tip.…”