Anomalous Hall effect in Y2Fe17-xCox single crystals

We study experimentally the Hall resistivity of Y2Fe17-xCox single crystals with x <= 4 for wide temperature and applied magnetic field ranges and for various magnetic field orientations with respect to the easy-magnetization axis. For small x, the anomalous Hall effect (AHE) is very anisotropic in these naturally layered compounds. For x <= 2, the AHE resistivity, measured with an applied magnetic field H perpendicular to c axis, is nearly 1 order of magnitude larger than the AHE resistivity for H along the hard-magnetization direction (H parallel to c axis). Furthermore, the former is very large and varies linearly with the longitudinal resistivity rho, whereas the latter increases as rho(2). The behavior of the AHE for H parallel to c axis comes quite likely from the intrinsic effect related to the hopping between different Fe d orbitals. Such hopping is allowed for high-symmetry points at the crystallographic dumbbell sites in this configuration. On the other hand, interorbital hopping is not allowed for H perpendicular to c axis. However, a huge amplitude of the AHE scattering for this configuration, which follows from skew scattering, is puzzling. Both the AHE anisotropy and the large skew scattering vanish for sufficiently high Co content. We attribute this to variations in the electronic structure of the Y2Fe17-xCox system when Co atoms start to occupy the dumbbell crystallographic sites.