Thermoelectric power and Hall effect in Co-Al-O granular films

We have measured the thermoelectric power and Hall effect on three Co-Al-O granular films whose conduction mechanism varies from metallic to tunneling type depending on O content. We obtained a finite thermoelectric power (TEP) which decreases with increasing resistivity. In the tunneling type sample, a large field dependence of TEP correlated with the magnetoresistance has been observed. The Hall coefficient of Co-Al-O decreases with, increasing sample resistivity, in contrast with the giant Hall effect reported for Ni-SiO2 granular sample with a similar resistivity. The dominant electronic conduction mechanisms are found to be different between the giant magnetoresistance and the giant Hall effect in ferromagnetic-metal-oxide granular systems.