MAGNETOELASTIC SOLITARY WAVES AND DOMAIN SUPERSOUND DYNAMICS

The domain wall (DW) dynamics in weak YFeO3-like ferromagnets is studied involving the magnetoelastic coupling with the acoustic subsystem of a crystal. A particular attention is paid for the range of the DW velocities close to the sound velocity, where such coupling has a resonance character. The equation is derived describing the DW and other nonlinear wave dynamics in a weak ferromagnet with taking into account of dissipation. and coupling with the crystal acoustic subsystem. This equation is reduced to the known sine-Gordon equation provided-the dissipation and magnetostriction constants vanish. The successive approximation method is proposed for determining the DW structure and velocity as a function of external magnetic field. it is shown that there is an anomaly in the DW velocity vs. magnetic field dependence near any sound wave branch. The main feature of the anomaly is the negative mobility segment where the planar DW steady motion is unstable. The magnitude of these magnetoelastic anomalies is shown to depend strongly on the direction of the DW motion with respect to the crystal axes. Within the reduced description in the terms of the DW gravity center coordinates the nonstationary dynamics of a wall and deformation accompanying it is studied. It is shown that during the DW braking a localized elastic deformation (elastic soliton) separates from the wall and propagates as a wavepacket with the longitudinal or transverse sound velocity. The character of the deformation space distribution and its time evolution is studied, agreeing on the whole with the experimental data obtained recently for the Mandelstam - Brillouin light scattering on a moving DW in YFeO3.