  The magnetoresistance (MR) and the magnetization isotherms were studied up to
high magnetic fields at T = 3 K and 300 K for a microcrystalline ($\mu$c) Ni
foil corresponding to bulk Ni and for a nanocrystalline (nc) Ni foil. At T = 3
K, for the $\mu$c-Ni sample with a residual resistivity ratio (RRR) of 331, the
field dependence of the resistivity was similar to what was reported previously
for high-purity ferromagnets whereas the MR(H) behavior for the nc-Ni sample
with RRR = 9 resembled that what was observed at low temperatures for Ni-based
alloys with low impurity concentration. In the magnetically saturated state,
the resistivity increased with magnetic field for both samples at T = 3 K and
the field dependence was dominated by the ordinary MR due to the Lorentz force
acting on the electron trajectories. However, the MR(H) curves were found to be
saturating for $\mu$c-Ni and non-saturating for nc-Ni, the difference arising
from their very different electron mean free paths. At T = 300 K, the MR(H)
curves of both Ni samples were very similar to those known for bulk Ni. After
magnetic saturation, the resistivity decreased nearly linearly with magnetic
field which behavior is due to the suppression of thermally-induced magnetic
disorder with increasing magnetic field. The MR(H) data were analyzed at both
temperatures with the help of Kohler plots from which the resistivity
anisotropy splitting ($\Delta\rho_{AMR}$) and the anisotropic magnetoresistance
(AMR) ratio were derived. It was demonstrated that at T = 300 K,
$\rho(H\rightarrow 0)=\rho(B\rightarrow 0)$ due to the negligible contribution
of the ordinary MR. The data for the two Ni samples at 3 K and 300 K were found
to indicate an approximately linear scaling of $\Delta\rho_{AMR}$ with the
zero-field resistivity. This implies that the AMR ratio does not vary
significantly with temperature in either microstructural state of Ni.
