SIMULATION OF 3-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 g arnet have been investigated using large scale numerical simulations. The width of a single pi-vertical Bloch line (pi VBL) at equilibrium h as 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 s pontaneous magnetization. A 2 pi VBL has been shown to be 1.5x wider t han a pi VBL. A comoving technique is used to track a single domain wa ll with a single pi VBL when a 5 Oe field is applied perpendicularly t o the surface of the film. At dynamic equilibrium, the VBL to wall vel ocity ratio is equal to ten, smaller than the value found for a simula ted loosely spaced chain of pi VBLs. A 2 pi VBL is split into two sing le 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 spin s is observed for the first 10 ns when a 30 Oe field is applied althou gh considerable spin distortion occurs in the wall center. When the fi eld is turned off after 8 ns, the relaxing distortion drives the surfa ce spins apart. The containment due to 2 pi horizontal Bloch line form ation during the process is demonstrated. (C) 1996 American Institute of Physics.