  We investigate the unusual temperature dependence of the anomalous Hall
effect in Ni. By varying the thickness of the MBE-grown Ni films, the
longitudinal resistivity is uniquely tuned without resorting to doping
impurities; consequently, the intrinsic and extrinsic contributions are cleanly
separated out. In stark contrast to other ferromagnets such as Fe, the
intrinsic contribution in Ni is found to be strongly temperature dependent with
a value of 1100 (ohm*cm)^(-1) at low temperatures and 500 (ohm*cm)^(-1) at high
temperatures. This pronounced temperature dependence, a cause of long-standing
confusion concerning the physical origin of the AHE, is likely due to the small
energy level splitting caused by the spin orbit coupling close to the Fermi
surface. Our result helps pave the way for the general claim of the Berry-phase
interpretation for the AHE.
