Tunnelling magnetoresistance of misfit layered cobaltite Ca3-xYxCo4O9 (x=0, 0.1, 0.2)

We have measured the electrical resistance and the high-field magnetoresistance (MR) up to 30 T for nano-scale misfit layered compounds Ca3-xYxCo4O9 (x = 0, 0.1, 0.2). The resistance shows the characteristic behaviour proportional to exp(rootT(0)/T) of the variable range tunnelling at low temperatures. The negative MR ratio increases remarkably with decreasing temperature and with increasing x at temperatures below 20 K. We propose that the MR in the cobaltite can be explained by the magnetic tunnelling effect.