Large magnetothermopower in La0.67Ca0.33MnO3 films

We have studied transport properties, including the thermopower and its field dependence, between 5 K and room temperature in films of La0.67Ca0.33MnO3, fabricated by simple metalorganic decomposition technique. A large negative magnetothermopower, [S(H)-S(O)]/S(O), amounting to as much as 38% has been observed in addition to a large negative magnetoresistivity, [rho(H)-rho(O)]/rho(O), with a peak value of 70% in a field of 5 T. S(H) is found to correlate with p(H) in the form S(H)proportional to lnp(H)+const while p(H,T) scales with magnetization according to rho(m)exp[-M(H,T)/M(0)] below the magnetic transition temperature. Above the transition rho(H)proportional to exp[-M(2)(H)], while rho(O) displays Arrhenius behavior. All these facts are consistent with a picture of electrical conduction being dominated by magnetic polaron hopping which has its origin in the local magnetic order.