Dynamical scaling and critical scattering in pure and disordered ferromagnets probed by NSE

We have studied the 3D Heisenberg ferromagnetic model system CdCr2xIn2−2xS4 in the ferromagnetic and reentrant phases as a function of temperature and momentum transfer using neutron spin echo (NSE) spectroscopy. The results from the pure sample CdCr2S4 are in excellent agreement with the predictions of the renormalization group theory. In the presence of disorder, we see the evolution from a simple critical ferromagnetic scattering with single fast relaxation times to a more complex slow dynamics characteristic of spin glasses.