Controlling percolation in field-structured particle composites:  Observations of giant thermoresistance, piezoresistance, and chemiresistance

Composites of conductive particles in an insulating phase are conductive if the particle volume fraction exceeds the percolation threshold. Composites prepared slightly above the percolation threshold have a conductivity that is sensitive to small volume changes, and thus have potential as temperature, pressure, or chemical sensors. In practice it is difficult to prepare composites close to the percolation threshold, and the critical current-carrying path gives a rather low sample conductivity. We find that magnetic-field-structured composites, consisting of gold-coated magnetic particle chains in a polymeric resin, can be reproducibly brought to the percolation threshold, regardless of particle concentration. The low-dimensionality conducting chains form a dense population of critical current paths with extreme sensitivity to composite volume changes. These field-structured composites thus exhibit giant thermoresistance, piezoresistance, and chemiresistance, and should be useful as sensor materials.