A STUDY OF THE DYNAMICS OF MAGNETIC BUBBLES DRIVEN BY A ROTATING GRADIENT WITH NO IN-PLANE FIELD
Abstract
The first experiment having the capability to observe undistorted dynamically stable twist structures in a moving magnetic bubble domain wall was performed. This bubble was rotated in a circular orbit for both senses of rotation. The wall structure was probed by comparing the experimentally obtained velocity-momentum relation with the predicted relations for various wall twist structures. Stray domain effects were observed at high drives in an unprotected test area by using high-speed photography. Numerical studies of the field well shape for high drives corroborated this observation. A conductor configuration that provides test-area isolation was fabricated, combinng the drive and isolation devices ina single level. Consistent results were obtained for the standard velocity versus longitudinal drive relation for both films studied, so it is concluded that for the rotating gradient method a unidirectional in-plane field is not necessary, and, moreover, it is actually undesirable since it violates the steady-state principles of the experiment. The Bloch curve structure was experimentally observed, with the Bloch curve nucleation threshold being different for the two surfaces of an ion-implanted film. As a result the velocity-momentum relation followed that predicted for one Bloch curve until the second curve nucleatd at the film surface. This nucleation was indicated by the transition between the one and two Bloch curve branches in the experimental velocity-momentum relation. A special technique was developed for the observation of domain contrast beneath opaque objects in a transmission-mode optical system. Finally, two key elements in the rotating gradient analysis, the rotating gradient drive assumption and the finite rectangular conductor section approximation were examined and were found to be useful models.
Degree
Ph.D.
Subject Area
Electrical engineering
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