Simulation of three-dimensional nonperiodic structures of pi-vertical Bloch line and 2 pi-vertical Bloch line in magnetic garnet

The dynamics of three-dimensional nonperiodic structures in magnetic garnet have been investigated using large scale numerical simulations. The width of a single pi-vertical Bloch line (pi VBL) at equilibrium has been measured to be twice the analytical Bloch line width pi(A/2 pi M(S)(2))(1/2), where A is the exchange energy constant and M(S) the spontaneous magnetization. A 2 pi VBL has been shown to be 1.5x wider than a pi VBL. A comoving technique is used to track a single domain wall with a single pi VBL when a 5 Oe field is applied perpendicularly to the surface of the film. At dynamic equilibrium, the VBL to wall velocity ratio is equal to ten, smaller than the value found for a simulated loosely spaced chain of pi VBLs. A 2 pi VBL is split into two single pi VBLs when an in-plane field is applied in the same direction as that of the center spin of the 2 pi VBL. No motion of the surface spins is observed for the first 10 ns when a 30 Oe field is applied although considerable spin distortion occurs in the wall center. When the field is turned off after 8 ns, the relaxing distortion drives the surface spins apart. The containment due to 2 pi horizontal Bloch line formation during the process is demonstrated. (C) 1996 American Institute of Physics.