Magnetic domain wall dynamics of bubbles in unimplanted and ion implanted (111) garnet films
Abstract
Generation of pairs of Bloch curves (BC) and vertical Bloch lines (VBL) occurs when the bubble translational velocity is monotonically increased. Changes in the value of the winding number (S) and the dimensionless momentum (p) are observed when a magnetic bubble is continuously translated in a circular trajectory by means of the rotating gradient experiment (RGE). Increases (decreases) in S are generally seen for clockwise (counterclockwise) circulation. The S value was confirmed with the rocking experiment from the deflection angle of the trajectory. Winding and unwinding transitions are reviewed for five unimplanted samples with different compositions and material parameters. The annihilation of VBLs on the bubble inner flank causes the changes in S. Any two +$\pi$ ($-\pi$) VBLs are found to stay together in moving and stationary bubbles. Bubbles with VBLs only on the inner flank make the bubble elliptical. This ellipticity increases with the number of VBLs. A model of the formation and transformation of VBLs is proposed. Magnetic-moment singularities produce VBL annihilation. Three samples, from the same wafer, implanted at 200KeV with Ne$\sp+$ at 0.5, 1 and 2 $\times$ 10$\sp{14}$ atoms/cm$\sp2$ are used to investigate dynamic transitions. Winding transitions are observed only in the lightly implanted film. Changes of p between transitions are a result of the size changes in BCs. The resistance of BCs to grow and punch-through and VBLs to translate are found to be larger in the implanted films and cause the velocity and p to increase further between transitions. Elliptical bubble trajectories are observed in the heavily implanted sample where the velocity changes with position due to an in-plane anisotropy. Dynamic transitions are investigated in the heavily implanted sample annealed at different temperatures in oxygen. This heat treatment partially removes implantation effects and winding transitions are observed for annealing temperatures larger or equal to 350$\sp\circ$C. The RGE parameter K$\sbsp{\rm E}{\rm r}$ is defined and used to determine the implantation and annealing effects.
Degree
Ph.D.
Advisors
Friedlaender, Purdue University.
Subject Area
Electrical engineering
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