Temperature Dependence of the Intrinsic Anomalous Hall Effect in Nickel
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.