MAGNETOTHERMOPOWER IN LA0.67CA0.33MNO3 THIN-FILMS

We have measured the thermopower S(T,H) and resistivity rho(T,H) of la ser ablated La0.67Ca0.33MnO3 films, as a function of temperature and e xternal magnetic field. On heating. a metal-insulator transition occur s at temperatures below The resistivity peak, observed via a jump betw een a low T regime, where S proportional to T, and a high T regime, wh ere S proportional to 1/T. An applied magnetic field shifts the transi tion in a postannealed sample to higher temperatures, causing a giant magnetothermopower effect 100x(S-8T - S-0T)/S-8T = -1400%. Both S(T) a nd rho(T) are activated at high temperatures, but with significantly d ifferent activation energies. We interpret this as an evidence of smal l polarons at high temperatures. (C) 1996 American Institute of Physic s.