Critical scattering in dilute ferromagnets

Abstract
A troubling aspect of dilute magnetism is the failure of the spin-spin correlation length, measured in neutron scattering, to diverge at TC. New data for (FepNi1−p)80P20 show an increase in critical scattering at small Q (≲0.02 Å−1) near TC. We propose, using scaling arguments, that a change occurs in effective correlation length from a finite 1D length at Q≫ξ−1p to a divergent 3D length for Q≪ξ−1p, where ξp is the geometrical connectedness length.