Ferromagnetic correlation lengths in dilute PdFe and PdCo alloys

A reanalysis of the unpolarised neutron magnetic diffuse scattering data for weakly ferromagnetic PdFe and PdCo alloys shows that it is the geometrical critical scattering model rather than the Marshall model (used by Low and co-workers) that provides a self-consistent interpretation of these data. Consequently the earlier deductions from these data of a large polarisation range (approx. 10 A) of an Fe or Co atoms in Pd and the relatively low solute concentrations at which the Pd atoms become magnetically saturated are incorrect. Instead it is argued that the polarisation range in Pd is probably not much larger than the nearest-neighbour distance and that ferromagnetism in Pd alloys arises through a percolation process involving ferromagnetic correlations between otherwise isolated polarisation clouds rather than through the direct overlaps of very spatially extended polarisation clouds. (author)