Mixed-valence manganites (A(0.7)(3+)B(0.3)(2+))MnO3 exhibit a resistiv
ity peak with giant negative magnetoresistance below the Curie point.
Residual resistivity ranges from 5 X 10(-8) to 8 X 10(3) Omega m, but
the electronic heat capacity when A = Y or La is that of a normal d-ba
nd metal; y approximate to 6 mJ mole(-1) K-2 Spatial fluctuations in t
he Coulomb and spin-dependent potentials localize the e(g) up arrow (s
igma) electrons in wave packets that are large on the scale of the Mn
-Mn separation. Transport in the magnetically localized state involves
zero-point-energy assisted hopping or tunneling of electrons from one
weakly localized wave packet to another.