  We investigate the low temperature magnetic field dependences of both the
resistivity and the magnetization in the misfit cobaltate Ca3Co4O9 from 60 K
down to 2 K. The measured negative magnetoresistance reveals a scaling behavior
with the magnetization which demonstrates a spin dependent diffusion mechanism.
This scaling is also found to be consistent with a shadowed metalliclike
conduction over the whole temperature range. By explaining the observed
transport crossover, this result shed a new light on the nature of the
elementary excitations relevant to the transport.
