Effect of substrate temperature on the spin transport properties in C60-based spin valves.

We report the effect of the substrate temperature on the magnetoresistance (MR) of 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 that all types of devices showed a monotonic increase in their MR ratio with the substrate temperature. Interestingly, an especially large MR (|-28.5%|) was obtained in the device fabricated at a higher substrate temperature, whereas for the other types of devices, the MR magnitudes were about a few percent. On the basis of the I-V measurements as well as SEM and AFM characteristics, we have found 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.