Geometrical Optics of Magnetoelastic Wave Propagation in a Nonuniform Magnetic Field

The propagation of magnetoelastic waves in a magnetic insulator having a nonuniform internal magnetic field is examined in the geometrical optics approximation. Hamilton's ray path equations are obtained from the slowness relation for the medium, and it is shown that for YIG there is a substantial focusing action in the rod configuration commonly used for magnetic delay line experiments. When external field shaping is used to produce a minimum internal field at the midpoint of the rod it is found that divergence of the magnetoelastic waves is to be expected.