Magnetoresistances (MR's) of quasi-two-dimensional purple bronzes AMo(6)O(17) (A=K, Tl, Na) are comparatively studied at 2 K for magnetic fields of Hparallel toc and Hperpendicular toc, respectively, where c is the direction normal to the two-dimensional plane of the sample. Unusually huge positive MR's for Hparallel toc are analyzed quantitatively by a two-band carriers galvanomagnetic effect on the ungapped residual Fermi surfaces, in which the concentration of the carriers is modified by an applied magnetic field. The modified two-band model can explain the MR's well, and the resulting parameters suggest that the purple bronzes belong to an uncompensated metal. [References: 30]
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