FeCl4− doped polyacetylene near the metalinsulator transition: Anomalous magnetoresistance at high fields up to H30T

We report on the anomalous high field magnetoresistance of FeCl 4 - doped polyacetylene films near the metal-insulator transition in the temperature range T = 0.6-1.4K and the magnetic field range H = 0-30T. When doped polyacetylene approaches to the metal-insulator transition region from the metallic side, the magnetoresistance of FeCl 4 - doped polyacetylene shows two positive peaks, which is different from the case of iodine or ClO 4 - doped polyacetylene showing only one broad peak. The results could he understood in terms of the compensation for the internal exchange field of a FeCl 4 - ion by the external high magnetic field.