MAGNETOTRANSPORT PROPERTIES OF MAGNETIC GRANULAR SOLIDS - THE ROLE OFUNFILLED D-BANDS

We calculate the magnetoresistance and magnetothermopower of magnetic granular solids. Contrary to previous theories of the giant magnetores istance (GMR), we demonstrate that the unfilled d bands of magnetic gr ains play an essential role in the transport properties of these syste ms. Our results relate GMR and magnetothermopower to microscopic and g eometric quantities, and provide a natural explanation for many experi mentally observed features, such as the (M/M(s))2 dependence of the GM R, the giant magnetothermopower and its 1/rho scaling behavior, and th e absence of negative GMR in rare-earth-nonmagnetic structures.