DYNAMIC CONVERSION OF A MAGNETIC BUBBLE IN A ROTATING GRADIENT EXPERIMENT
Abstract
The rotating gradient experiment is a method for the study of bubble dynamics in which a magnetic bubble is propagated in circular steady-state motion. From a measurement of the radial force acting on the moving bubble, the winding number and momentum of the bubble can be determined, making possible a determination of its dynamical Bloch line structure. The rotating gradient method was used to study dynamic conversion, a change in the Bloch line structure (state change) of a magnetic bubble that results from its traveling at a sufficiently high velocity. The state changes were effected by bringing the bubble to a critical velocity at which a Bloch curve will punch through. No in-plane fields were used in the experiments. In a Y(,1.52)Eu(,0.3)Tm(,0.3)Ca(,0.88)Ge(,0.88)Fe(,4.12)O(,12) sample with an implant of 1 x 10('14) Ne, the unichiral bubble was dynamically converted into a bubble with a more complex domain wall structure. At least five distinct states were generated and were identified by determining the winding number and momentum from the velocity vs. radial drive relation. The data provides evidence for the dynamic generation of vertical Bloch lines, Bloch curves, and Bloch points, the latter being evidenced by fractional winding number states. The bubble returned to the S = 1, unichiral state when motion ceased. The peak translational velocity was 18 m/s, compared to the theoretical Bloch curve punch-through velocity of 27 m/s. In an unimplanted low damping sample, (YLa)(,3)(FeGa)(,5)O(,12), known as AC4-33, the dominant dynamic conversion process was the addition of opposite twist vertical Bloch line pairs to the domain wall. As many as five vertical Bloch line pairs were added to the domain wall of the unichiral bubble; the number of which was identified from the momentum measurement. Dynamic conversion was also investigated for starting bubble states S = -1, S = 0, and S = 3. In AC4-33, the experimental punch-through velocity is 4 m/s; the theoretical one is 20 m/s. The tickle field (0.15 Oe amplitude, 5.5 MHz) that was superposed on the dc bias was found not to affect the Bloch curve punch-through velocity. Results of calculations that describe the influence of experimental parameters on dynamic conversion in this experiment are presented.
Degree
Ph.D.
Subject Area
Electrical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.