We present a detailed study of the activated resistivity of La0.6Ca0.33MnO3
films up to 600 K under the influence of high magnetic fields. Data in zer
o field can be explained by small polaron hopping as treated in the Friedma
n-Holstein theory. Based on the spin orientation of ferromagnetic clusters
in a magnetic field, we develop a phenomenological model describing the tem
perature and field dependence of the resistivity with a minimum of free par
ameters. We find that the polarons have a magnetic contribution to their ac
tivation energy for hopping which depends on the variation of the spin orde
r with increasing temperature and can be modified by applied magnetic field
s. The average magnetic clusters contain 4-6 ions. Hall measurements show a
temperature dependent electronlike linear low field slope predicted by the
theory of the Hall mobility of small polarons. [S0163-1829(98)04646-3].