Magnetic-field-sensitive polymer composite materials

This paper reports the results of investigations on magnetoresistance in composite materials prepared by direct polymerization of propylene on graphite particles. The method ensures grafting of polymer to the filler surface, imparting remarkable properties to the composite. For composites with graphite, magnetoresistance is positive for a filler volume fraction above the percolation threshold. The maximum value of magnetoresistance exceeds 10 percent. Below the threshold the samples show weak negative magnetoresistance characteristic of conduction through localized states in disordered systems. This result correlates with our model of double percolation over filler particles, surrounded by thin layers of injected charge. New magnetic effects have been found, such as oscillations of dark conductivity in magnetic field and resonance magnetic-spin effects. (Author)