We describe the transport characteristics and the observation of a type of magnetoresistive behavior in nonmagnetic nanocompacts, consisting of mixtures of Ag and PbO nanoparticles packed into compact units at various mass compositions and compacting densities. Semiconductorlike, intermediate, and metallic transports may all be revealed by tuning the compacting density. Crossovers from a positive magnetoresistance (MR) at low applied magnetic fields to a negative MR at high fields were observed in the loosely packed units. No evidence of MR saturation was seen up to an applied field of 9 T. Raising the temperature suppresses the MR responses. Surprisingly, no noticeable differences in the MR responses were found for samples with different $\mathrm{Ag}∕\mathrm{Pb}\mathrm{O}$ compositions. The observed transport characteristics fit well to the tunneling transport, and the MR characteristics may be described as being the tunneling transport between Zeeman split discrete Fermi states of weakly linked nanoparticles.

• Received 10 January 2005

DOI:https://doi.org/10.1103/PhysRevB.72.113406