“Light” and “Heavy” Domain Walls in Bubble Films

Abstract

A theory concerning the static and dynamic behavior of domain walls in bubble films is described. Several different wall types exist, which have different twist angles (angle between the wall magnetization at the midplane of the film and at the film surface). The wall structure with the lowest energy has a twist angle of approximately π/2 (for thick films). A wall structure having a twist angle of approximately −3π/2 is also stable and has only a slightly larger energy, but a much larger effective mass. The ratio of the energy of a twisted (light or heavy) wall to the energy of an untwisted wall can for thick films be represented as E/Eo= (1−βσ)1/2 (where σ = 4πM/Ha, Ha = anisotropy field, M = saturation magnetization). For light walls β ≃ 0.69 whereas for heavy walls β ≃ 0.69 − (π/c) (D/2πM)1/2. Here 2c is the film thickness, D = 2A/M, and A the exchange stiffness constant. For light walls the ratio of the wall mass in films to the wall mass in an infinite medium is ≳ 1.75 (1 −σβ)1/2. For heavy walls thi...