Raman Scattering by Magnons in Rare Earth Metals

A theory of light scattering in a magnetic metal using the spin-dependent electric polarizability is developed and is applied to Raman scattering by magnons inn heavy rare earth metals. An important mechanism for one- and two-magnon scatterings arises from the coupling of radiation field with the 4 f localized moments via spin-orbit interaction. There are also indirect mechanisms in which electric polarizability of the conduction electrons are modulated by the s - f exchange interaction. Contributions of these mechanisms to the spin-dependent polarizability are estimated. We present calculations of the scattering symmetries and intensities for one- and two-magnon processes in systems with ferro-magnetic, spiral and conical spin structures, with application to Tb and Dy, assuming the first mechanism is predominant. In the cases of spiral and conical structures the magnons with wave vectors ± k 0 and ±2 k 0 are excited, where k 0 is the wave vector describing the periodicity of the static spin arrangement.