Elliptical distortion and bias compensation in the gradient propagation of bubble domains

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Abstract
Using high-speed photography in a pulsed gradient field experiment we have studied the elliptical and radial distortion of bubble domains during propagation as a function of bias compensation, pulse width, and drive. We propose a theory which relates the gyrotropic forces exerted by the Bloch-line pairs to the elliptical and radial distortion. As a function of bias compensation a peak appears in both the distortion and ballistic overshoot data at a point which closely coincides with the proper calculated value of bias compensation. The elliptical distortion and radial expansion at the peak are found to agree quite closely with theory at short pulse widths and low drives. At values of bias compensation different from the proper calculated value significant deviations from theory occur. In these cases the bubble losses its closely elliptical shape, becoming slightly asymmetrical, suggesting unequal generation of Bloch lines on its front and rear wall sections.