Cellular domain patterns in magnetic garnet films.

摘要

This thesis presents the first experimental study of two-dimensional cellular patterns of magnetic domains in garnet films. Room-temperature observations focused on a Bismuth-substituted film designed for magneto-optic device applications. Measurements of energies and statistical quantities were aided by computer analysis of digitized pattern images. An external bias field {dollar}Hsb B{dollar} induces pattern evolution that is shown to be governed by three elemental domain structures: (i) Stripe segments that form the cell boundaries. Magnetic field and domain wall energies produce effective tension in the stripe segments that drives the domain motion. (ii) 3-fold vertices that join the stripe segments. Cellular patterns saturate when the vertices are destroyed at the bias value {dollar}Hsb{lcub}V{rcub}{dollar} (= 0.79 {dollar}times 4pi M{dollar} = 150 Oe), the largest saturation field of all domain pattern topologies. (iii) Pentagonal bubble traps, 5-fold symmetric structures containing trapped magnetic bubble domains. Isolated bubble traps collapse at a critical bias field {dollar}Hsb5{dollar} (= 0.54 {dollar}times 4pi M{dollar} = 103 Oe). A simple geometric model illustrates the energetic mechanism of bubble trap collapse. An analytic pattern model accounts for domain interactions so as to elucidate the bias and configuration dependence of the stripe tension and outline the energetic bias regimes. All stripe segments are under tension in the nonequilibrium regime {dollar}Hsb{lcub}RI{rcub}