Orientation Dependence of the Intrinsic Anomalous Hall Effect in hcp Cobalt

We carry out first-principles calculations of the dependence of the intrinsic anomalous Hall conductivity of hcp Co on the spin magnetization direction. The Hall conductivity drops from 481 to 116 S/cm as the magnetization is tilted from the easy axis (c axis) to the ab plane. These values agree reasonably well with measurements on single crystals, while the angular average of 226 S/cm is in excellent agreement with the value of 205 S/cm measured in polycrystalline films. The strong intrinsic anisotropy is shown to arise from quasidegeneracies near the Fermi level.