Fig. 14.9. Temperature dependence of the Hall coefficient RH(T) for K3Cœ [14.45],

For many materials, the Hall coefficient and the Seebeck coefficient provide complementary information on the sign of the dominant carrier and the carrier density. Since the MXC60 compounds pertain to carrier occupation of several bands, the connection between the Hall coefficient and the Seebeck coefficient (see §14.12) is less direct than for simple one-band metals. Nevertheless, it is of interest to observe the similarity of behaviors of Rh(T) for KaQo and K4C7(), on one hand, and the temperature-dependent thermopower S(T) behavior for the same compounds (see §14.12).

14.4. Magnetoresistance

Most of the emphasis thus far given to study the magnetic field dependence of the resistivity has gone into study of the shift of the superconducting transition temperature with magnetic field [14.17,18,45], and this topic is discussed in §15.3. Few experiments have, however, been done to study the temperature and magnetic field dependence of the magnetoresistance in the normal state. The magnetoresistance is typically defined as (Ap/p0) = [p{H)~ p(0)]/p(0). The most extensive normal state magnetoresistance studies presently available are for K3C60 [14.16] and K4C70 [14.26] film samples, where the emphasis was to use the T and H dependence of Ap/p0 to gain understanding of the nature of the disorder for K3C60 and K4C70 thin films.

As a function of magnetic field, the magnetoresistance Ap/p0 observed for thin-film K3C60 samples (see Fig. 14.10) for temperatures up to 30 K and fields up to 15 tesla was divided into two terms

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