A theory is presented for light scattering in disordered magnetic systems using a scattering Hamiltonian for which the incident radiation is transformed from the laboratory frame to the local frames on the spins, and the scattered radiation back. The light-scattering cross sections involves a sum over all the wavevectors, as well as a sum over all the configurational averages of the dynamic susceptibilities of the different magnetic modes of the spin system of the material. All wavevectors contribute as a consequence of the breakdown of wavevector selection rules due to the lack of translational invariance in these systems. The sum over all the dynamic susceptibilities is a consequence of the incident light coupling to all the modes via a magnetic structure factor, since the spins are oriented at random in a disordered magnetic system. The site disorder which gives different scattering strengths per site is treated kinematically by a mapping procedure previously used for the n-sublattice ferrimagnet, n being arbitrarily large. The theory is applied to light scattering in amorphous ferromagnets and spin glasses. It is found that scattering occurs from transverse and longitudinal excitation in amorphous ferromagnets, and from diffusion excitations in spin glasses.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics