Study of slow dynamic processes in magnetic systems by neutron spin-echo spectroscopy

The use of the neutron spin echo (NSE) technique in the study of slow dynamic processes in magnetic systems is reviewed. NSE provides the highest energy resolution of all inelastic neutron scattering techniques, hence it is used mainly in studying systems that show very slow dynamics, which cannot be resolved otherwise with neutrons. For spin glasses, which show a dramatic slowing down of the spin dynamics in the vicinity of T_g, research using NSE has made significant contributions to our understanding of the nature of the phase transition and the line shape of the spin relaxation function. In the study of the critical dynamics in magnets, NSE has proven predictions of dynamic scaling theory to be correct. Geometrically frustrated magnets and their unusual properties at low temperature have seen an upsurge of interest in recent years, and NSE has been able to make some key contributions to this field. The case of Gd₂Ti₂O₇ is presented in some detail, a system in which ordered spins and paramagnetic spins coexist.