Anomalous Hall resistivity of cobalt films: Evidence for the intrinsic spin-orbit effect

We report the anomalous and ordinary Hall resistivities, ρ_AH(T) and ρ_OH(T), measured on 10–200 nm thin polycrystalline Co films between 50 and 350 K. Analyzing ρ_AH in terms of the zero-field resistivity ρ(T) reveals the Hall conductivity σ_xy as the dominant contribution , while impurity induced skew scattering remains much smaller. Since, in contrast to ρ(T), the Hall conductivity turns out to be independent of structural disorder and phonons, σ_xy=240 Ω cm⁻¹ should entirely be determined by the spin-orbit split band structure, as it was proposed in early theories and, more recently, realized for Fe by calculations of the k-space Berry phase of occupied Bloch states [ Yao et al. Phys. Rev. Lett. 92 037204 (2004)]. Also, our results rule out a recent, modified skew-scattering model for ρ_AH.