The low-frequency 1/f resistance fluctuations of epitaxial La2/3Ca1/3MnO3 t
hin films on different substrates have been studied as a function of temper
ature and applied magnetic field. A film with a high Curie temperature T-C=
250 K grown on a substrate with perfect lattice match (NdGaO3) shows a low
overall noise amplitude, comparable to that of a conventional metal. In con
trast to previous work, no increase of the 1/f resistance noise in the ferr
omagnetic regime of the La2/3Ca1/3MnO3 film could be observed. The magnitud
e of the normalized resistance fluctuations decreases with decreasing tempe
rature except for a sharp peak at T-C this peak is completely suppressed by
an applied magnetic held of about 2 T. In contrast, the noise level in a f
ilm with low Curie temperature (T-C = 110 K) grown on a substrate (SrTiO3)
with large lattice mismatch (1.5%) is several orders of magnitude larger an
d shows a qualitatively different temperature dependence, with a huge noise
increase below T-C. These results are discussed in terms of a strong coupl
ing of electric resistance and magnetic ordering, as well as within a perco
lative picture of the ferromagnetic transition.