Collective Coordinate Study Of Spin-Wave Emission From A Dynamic Domain Wall

We study theoretically the spin-wave emission from a moving domain wall in a ferromagnet. Introducing a deformation mode describing a modulation of the wall thickness in the collective coordinate description, we show that thickness variation couples to the spin wave linearly and induces spin-wave emission. The dominant emitted spin wave turns out to be polarized in the out-of wall plane (phi) direction. The emission contributes to the Gilbert damping parameter proportional to h omega(phi)/K, the ratio of the angular frequency omega(phi) of phi, and the easy-axis anisotropy energy K.