Theory of spin fluctuation resistivity below the critical point

The authors study the DC electrical conductivity of an itinerant electron system coupled to localised spins in a model intended to describe the rare earth metals at temperatures close to the magnetic transition point, with particular attention focused on the role of long-range order below the critical point. It is shown that, in the Born approximation, the critical indices for the specific heat (of the combined electron-localised-spin system) and the temperature derivative of the resistivity are the same both above and below the critical point. In particular, the singular temperature dependence of the resistivity immediately below T c is not determined by the order parameter, neither directly nor indirectly through the associated deformation of the Fermi surface. Instead, the short distance spin pair correlations play the dominant role. These conclusions are not based on specific assumptions about the type of magnetic order or the shape of the Fermi surface.