We have studied transport properties, including the thermopower and its field dependence, between 5 K and room temperature in films of ${\mathrm{La}}_{0.67}$${\mathrm{Ca}}_{0.33}$Mn${\mathrm{O}}_3$ fabricated by simple metalorganic decomposition technique. A large negative magnetothermopower, $\frac{\mathrm{}\left[S\right(H)-S(0\left)\right]}{S\left(0\right)\mathrm{}}$, amounting to as much as 38% has been observed in addition to a large negative magnetoresistivity, $\frac{\left[\rho \mathrm{}\right(H)-\rho \mathrm{}(0\left)\right]}{\rho \mathrm{}\left(0\right)\mathrm{}}$, with a peak value of 70% in a field of 5 T. $S\left(H\right)\mathrm{}$ is found to correlate with $\rho \mathrm{}\left(H\right)\mathrm{}$ in the form $S\left(H\right)\mathrm{}\propto \ln \rho \mathrm{}\left(H\right)+\mathrm{const}$ while $\rho (H, T)$ scales with magnetization according to ${\rho }_m\exp [-\frac{M(H, T)}{M_0}]$ below the magnetic transition temperature. Above the transition $\rho \mathrm{}\left(H\right)\mathrm{}\propto \exp [-M^2\mathrm{}(H\left)\right]$, while $\rho \mathrm{}\left(0\right)\mathrm{}$ 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.

• Received 25 September 1995

DOI:https://doi.org/10.1103/PhysRevB.53.5094