THE EFFECT OF HIGH MAGNETIC-FIELD ON THERMOELECTRIC-POWER OF DOPED POLYACETYLENE

We have measured the temperature dependent thermoelectric power (TEP) of doped polyacetylene (PA) under the high magnetic field up to 20 tes la. The dopants are I-2, FeCl3, AuCl3 and NbCl5. The overall temperatu re dependence is characteristic to that of the diffusive metals, i.e. the TEP is positive and it decreases quasi-linearly upon cooling. Howe ver, the zero field TEP, S(T, H=0T), shows significant differences bet ween the iodine doped PA and the other metal-halide doped ones at low temperature. While the S(T, H=0T) for iodine doped PA is quasi-linear in temperature down to 4.2 K, the S(T, H=0T) of metal-halide doped sam ples become temperature independent below T congruent to 20 K and some of them show even negative TEP with a broad minimum peak at low tempe rature. At H=20T, both iodine and metal halide doped PA shows an abrup t decrease of 1 similar to 2 mu V/K in TEP at T similar to 70K, except the most heavily doped [CH(AuCl4)(y)](x) where no such drop appears. In the low temperature region, the Delta S(T)=S(T,H=20T)-S(T,H=0T) of metal-halide doped PA becomes more negative and the minimum peak of TE P shifts slightly to higher temperature. Similar tendency is observed at zero field TEP of [CH(AuCl4)(y)](x) as we increase the doping conce ntration y. For the iodine doped Pq the low temperature Delta S(T)=S(T ,H=20T)-S(T,H=0T) is more or less the same as that of T similar to 70K where the abrupt jump occurred, i.e., the S(T,H=20T) of iodine doped PA remains quasi-linear as a function of temperature down to 4.2 K. Th e magneto resistance rho(T,H) of these samples is also measured and th e results are compared with the above S(T,H) data. Since no appreciabl e amount of anisotropy of the stretch oriented PA with respect to the applied magnetic field direction is observed in S(T,H) and rho(T,H) an d furthermore, because of the significant difference of S(T,H) between the iodine doped PA and the metal-halide doped ones, the spin-spin in teraction between the conduction electron spin in the metallic PA chai n and the localized spin in the metal-halide dopant located nearby the polymer chain could be the prime origin of the observed magneto TEP p henomena.