0 50 100 150 200 250 300 best fit to the experimental points Temperature ( K ) [18.18], spectively [18.26] (see §12.7.6). It is expected that K,C70 and K4C70 would have maxima in spin concentration due to the half-filling of their LUMO and LUMO+1 bands, respectively. The K4C70 phase is supposed to be more conducting than the K^o phase owing to its higher density of states
In addition to the Pauli paramagnetism due to conduction electrons, a Curie-Weiss paramagnetic contribution due to localized moments is observed (see Fig. 18.4) and is discussed in §18.5.
In the case of fullerenes, there is also the possibility of observing unusual magnetic behavior, associated with unfilled carbon p levels, because of the localization of electrons and spins on fullerene molecules. Normally Curie paramagnetism is associated only with unfilled d and / levels. Two examples of this unusual phenomenon of p-level magnetism have been reported and are described below. In the first case, the magnetic effect is associated with an insulator (Cs4C60), while in the second example, the magnetic species is an organic conductor (TDAE-C60).
Measurements of the magnetic properties of Cs-doped C60 [18.18,19] show unexpected behavior in the susceptibility, which implies that for some Cs concentrations, the molecular ions have magnetic dipole moments. As discussed in §18.4, the magnetic susceptibility for negatively charged fullerene ions Cg0~ is described by a constant term Xo and a Curie-Weiss term xcw
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