Magnetoresistance in Composite Devices Containing Nanoparticles of Fe3O4and Resin

Various composite devices consisting of nano- and/or microparticles and epoxy resin have been fabricated without heat treatment using a coagulant. The composite including the nanoparticles and the resin showed a rather considerable negative longitudinal magnetoresistance of about -5% compared with the composite including the microparticles. The average tunnel barrier thickness among particles of the composite containing the microparticles was about 2.7 times larger than that of the composite containing the nanoparticles. In both composites containing the micro- and nanoparticles, it was found that the slope of the pressure dependence of the resistance changed suddenly near 20 and 5 MPa in the compression and decompression processes, respectively. This shows that a change in the transport mechanism occurred owing to the pressure. The effects of the dispersion of nano- and/or microparticles and resin in the composite on the transport properties are also discussed.