Zur Streuung langwelliger Magnonen an Gitterfehlern

The scattering of ferromagnetic magnons by point defects is calculated within the framework of a phenomenological theory. This theory essentially takes account of the magnetic dipole interaction, and the magnetoelastic interaction, which are usually neglected. The scattering is due to an effective magnetic field, which is produced by the longrange strains of the lattice. For small wavenumbers this effective field is more important than the local disturbance of the exchange coupling in the vicinity of the defect, which hitherto has been considered almost exclusively, within the Heisenberg model. Due to the magnetic dipole interaction, the scattered wave and the differential cross section depend on the angle in a rather complicated manner: For each direction of scattering there are up to three groups of scattered waves, running away from the defect with different velocities. The differences between the classical and the quantum mechanical calculation are worked out.