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 ͑MR͒ 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 Ag/ PbO 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.Several types of magnetoresistive behaviors have been identified. Among them giant magnetoresistance 1 ͑GMR͒ originating from spin-dependent scattering, tunneling magnetoresistance 2 ͑TMR͒ from spin-dependent tunneling, ballistic magnetoresistance 3 ͑BMR͒ from domain wall scattering, and colossal magnetoresistance 4 ͑CMR͒ from the metal-insulator transition are all associated with the presence of magnetic ions. For nonmagnetic systems, there are extraordinary magnetoresistance 5 ͑EMR͒ originating from geometric scattering and quantum magnetoresistance 6,7 ͑QMR͒ from single Landau band transport are both found in semiconductor systems. Here, we report on the observation of a type of magnetoresistance in nonmagnetic Ag/ PbO nanocompacts, and the alternations in tunneling transport resulted from Zeeman splitting were used to describe the observed MR characteristics.The fabrication of macroscopic amounts of various types of ultrasmall nanoparticles has recently become feasible. A class of materials can now be created by assembling various kinds of nanoparticles of various mass compositions and compacting densities into compact units. This class of nanocompacts consists of ensembles of mutually linked nanometer grains, where the compacting density is the parameter that reflects the interparticle links. The Ag and Pb nanoparticles used in the present studies were fabricated by the gas condensation method, 8 employing an Ar evaporation atmosphere ͑0.1-2 Torr͒ and with the collector maintained at the liquid nitrogen temperature. The samples thus obtained were in powder forms, consisting of macroscopic collections of individual nanoparticles. The PbO nanoparticle powder was obtained by exposing the Pb nanoparticles to an oxygen atmosphere. X-ray diffraction measurements showed that it was slightly oxygen deficient PbO 0.97 , and no traces of the other oxidation phases were found within the 3% x-ray resolution limitation. The mean particle diameters, as determined from the x-ray diffraction profiles and the atomic force microscopy ͑AFM͒ images,...

Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles J. Appl. Phys. 112, 073926 (2012); 10.1063/1.4757418Comparative study on size dependence of melting temperatures of pure metal and alloy nanoparticles Appl. Phys. Lett. 99, 013108 (2011); 10.1063/1.3607957Effect of particle size and annealing on spin and phonon behavior in TbMnO3