S 1 2771 183

Although progress has been made in preparing endohedrally doped fullerene molecules, the yield has not yet been sufficient to study their magnetic properties in the solid state. From Table 18.2, it is seen that there are a variety of rare earth ions which can introduce magnetism into fullerenes by endohedral doping.

In considering the solid state, a magnetic phase could also be achieved by the exohedral doping of magnetic ions into tetrahedral or octahedral sites (see §8.5), in analogy with the magnetic properties observed in intercalation compounds based on graphite or transition metal dichalcogenide host materials (e.g., C6Eu).

18.3. Magnetic Properties of Fullerene Ions

Interestingly, the three ions that have been most commonly used as endo-hedral dopants into fullerenes (La3+, Y3+, and Sc3+) all have J — 0 (non-degenerate) ground states by Hund's rule (see §12.4.1) and therefore have no magnetic moments. Assuming no charge transfer to the C60 shell, no Jahn-Teller distortion would be expected for a single endohedral atom placed at the center of a C60 molecule. However, the insertion of La3+, Y3+ or Sc3+ gives rise to charge transfer (up to three electrons for each +3 ion). Since the ground state for a charged C60 ion differs from that of a neutral C60 molecule, a magnetic moment on the shell can result from charge transfer. In Table 18.3 are listed the ground state configurations for C^f molecular ions in icosahedral symmetry, the corresponding ground state

Table 18.3

Pauli-allowed states associated with the ground state configurations for icosahedral CJf ions.

Table 18.3

Pauli-allowed states associated with the ground state configurations for icosahedral CJf ions.

n

Config."

If, state6

] value'

Icosahedral symmetry of configurations

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