Skew scattering of electrons in metals can produce the anomalous and spin Hall effects. The microscopic mechanism is normally considered to be either the intrinsic effect of the crystal lattice or scattering from impurities, with the spin-orbit interaction in each case providing the coupling between the spin and the displacement of the electrons. As this is a relativistic effect, it is weak, and this is one of the obstacles to making and detecting spin currents. An alternative mechanism for skew scattering is from collective spin excitations in cooperatively ordered magnets and I will discuss this, with reference to specific alloys. I will discuss the effects of critical spin fluctuations in a ferromagnetic metal on anomalous and spin Hall effects as have been observed in both ferromagnetic alloys [1,2] and spin glasses [3]. As well as exploring possibilities for skew scattering this may provide probes of novel spin correlations in such materials, as the skew scattering is sensitive to higher order correlation functions than usually measured. I will discuss the relation to non-linear susceptibilities.

The theoretical work is in collaboration with Bo Gu and Sadamichi Maekawa, (ASRC, JAEA), Yasuhiro Niimi (U. Osaka), Yoshichika Otani (U. Tokyo), Albert Fert (Thales/CNRS) .

[1] D. H. Wei, Y. Niimi, B. Gu, T. Ziman, S. Maekawa, and Y. Otani,’ The spin Hall effect as a probe of nonlinear spin fluctuations’ Nat. Commun. **3**, 1058, (2012).

[2] B. Gu, T. Ziman, S. Maekawa, ‘Theory of the spin Hall effect, and its inverse, in a ferromagnetic metal near the Curie temperature’, Physical Review B **86**, 241303(R) (2013).

[3] Y. Niimi, M. Kimata, Y. Omori, B. Gu, T. Ziman, S. Maekawa, A. Fert, and Y. Otani , 'Strong Suppression of the Spin Hall Effect in the Spin Glass State’, Phys. Rev. Lett., **115,** 196602(2015).