Domain walls in bubble films. IV. High-speed wall motion in the presence of an in-plane anisotropy

Abstract

The effect of an in-plane anisotropy (such as occurs in orthoferrites due to the orthorhombic crystal structure) on the static and dynamic wall structure has been calculated for walls that are either parallel (ψ=0) or perpendicular (ψ=π/2) to the secondary (i.e., in-plane) anisotropy axis. The results are described in terms of a parameter η=Δ/2πM²₀, where Δ is the strength of the in-plane anisotropy and M₀ the saturation magnetization. For ψ=0, the critical points of the static wall structure move towards the film surface as η increases. For ψ=π/2, they move towards the midplane of the film where they merge for η→1. For ψ=π/2, η≫1, an untwisted wall becomes energetically favored over the twisted wall. The critical velocity at which wall motion becomes unstable is strongly dependent on η. For η<1 the lowest velocity threshold is due to Bloch-line nucleation at a critical point, for ψ=π/2, η<1, it is due to punch-through of the already existing Bloch line. For ψ=0 the critical velocity generally increases with increasing η. For ψ=π/2 the nucleation threshold at first decreases with increasing η and then increases. The punch-through threshold is substantially independent of η. For η≫1 the critical velocities for a film are substantially the same as for an infinite medium.