State changes in a moving bubble induced by a pulsed bias field

Tamara Jo Wilson Bettinger, Purdue University

Abstract

Uniaxial ferrimagnetic garnet films are the storage medium used in bubble memories. They are also the material to be used in the Bloch line memory proposed by Konishi in 1983. In the proposed Bloch line memory, Bloch lines are dynamically generated, and winding pairs of vertical Bloch lines (VBL's) are used as units of information storage. One proposed method of VBL propagation is by pulsed bias fields. In a Bloch line memory, the generation of Bloch lines must be reproducible, and the generated Bloch line pairs must be mutually annihilate. The effect of bias field pulses on a bubble in steady-state motion in the rotating gradient apparatus was investigated. Bias pulses with varying rise times and amplitudes were applied to a circulating bubble. Bias pulses can result in the creation of annihilation of an unwinding vertical Bloch line pair. The pulse amplitude required to cause an increase or decrease in the number of Bloch lines increases as rise time increases. The pulse amplitude required to annihilate a Bloch line pair is approximately the same as that required to create a pair. The mechanism for Bloch line creation is modeled as the growth and punch-through of a Bloch curve when the domain wall reaches a critical velocity. Bloch line annihilation occurs when the unwinding Bloch line pairs are propelled towards each other by the gyrotropic force and mutually unwind. The models proposed for the addition or annihilation of a Bloch line pair agree with the experimental data well enough to support their correctness. The experiments show clearly that Bloch curve nucleation is dependent on wall velocity. These data provide further support for the Bloch line theory of state changes. The experimental data on annihilation of a vertical Bloch line pair put a lower limit on Bloch line mobility.

Degree

Ph.D.

Advisors

Nyenhuis, Purdue University.

Subject Area

Electrical engineering

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