  We report the effect of the substrate temperature on the magnetoresistance
(MR) of the C60-based spin valve (SV) devices with the sandwich configuration
of La0.67Sr0.33MnO3 (LSMO)/C60/cobalt (Co). The C60 interlayer deposited at
different substrate temperatures resulted in four types of devices. We observed
all types of devices showed a monotonic increase in MR ratio with the substrate
temperature. And more interesting, an especially large MR (28.5%) were obtained
in the device fabricated at higher substrate temperature, while for the other
types of devices, the MR magnitudes were just about a few percent. Based on the
I-V measurements, as well as SEM and AFM characteristics, we have obtained that
the higher substrate temperature can cause many pits and hollows in the organic
film, and these pits will increase the tunneling probability of spin-polarized
carriers from one ferromagnetic electrode to the other.
