Spin Excitations in Localized and Itinerant Magnets
  Collective excitations in magnetic materials can be investigated by means of inelastic neutron scattering. We show that this experimental method gives access to the complete spectrum of magnetic fluctuations through the energy- and momentum-dependence of the dynamical susceptibility. We focus on the dynamical properties of magnets with localized spin densities and of metals.   From such studies, microscopic parameters like exchange integrals, spin-wave stiffness and relaxation times can be determined. This is of great help to test current theories in magnetism. 
B. Roessli and P. B\"oni