LONGITUDINAL MAGNETORESISTANCE IN POLYETHYLENE TEREPHTHALATE FILM.

The longitudinal magnetoresistance ( DELTA rho / rho //0) of polyethylene terephthalate (PET) film of thickness 125 mu m has been measured both in glassy and rubbery state in electric field up to 80 multiplied by 10**5 V/m and in magnetic field up to 0. 27 kG. The sample showed negative magnetoresistance at 393 K at a low electric field. The explanation of negative magnetoresistance is made in terms of scattering by localized spins. The electric field produces an opposite effect in glassy and rubbery state of the polymer, i. e. the magnetoresistance decreases with electric field at and below 378 K, on the other hand DELTA rho / rho //0 increases with electric field above 378 K. The energy gap at zero magnetic field is widened and shortened with electric field, in glassy and rubbery state respectively, which affects the carrier mobility and hence the magnetoresistance.