  We report resistivity and Hall effect results on Ba(Fe1-xNix)2As2 and compare
them with those in Ba(Fe1-xCox)2As2. The Hall number RH is negative for all x
values from 0.01 to 0.14, which indicates that electron carriers dominate the
transport both in the magnetic and paramagnetic regime. We analyse the data in
the framework of a two-band model. Without any assumption on the number of
carriers, we show that the electron resistivity can be estimated with good
accuracy in the low temperature paramagnetic range. Although the phase diagrams
of the two families are very similar with respect to the extra electrons added
in the system, we find that the transport properties differ in several aspects.
First, we evidence that the contribution of holes to the transport is more
important for Ni doping than for Co doping. Secondly, Ni behaves as a stronger
scatterer for the electrons, as the increase of the residual electron
resistivity rho/x is about four times larger for Ni than for Co in the most
doped samples.
