Statics and dynamics of magnetic domains and domain walls in orthorhombic garnet films

Dale O. Musselman, Purdue University

Abstract

This thesis is concerned with the statics and dynamics of orthorhombic garnet films, which have a medium-hard anisotropy axis in the plane of the film. Various static and dynamic experiments and analyses are described, including the first circulation experiments with orthorhombic films. After a brief overview of the micromagnetics of garnet films, a description is given of wall structures and previously-proposed static bubble states in orthorhombic films, along with a review of some experimental support for the state models. The rotating-gradient system and operating equations for uniaxial films are reviewed. A brief investigation is made of the conductor model used to compute drive fields, in view of the (sometimes large) discrepancy between computed and measured fields, and an enhanced conductor model is introduced. Preliminary measurements are reported of the temperature rise due to conductor Joule heating for glass and sapphire conductor substrates, showing s substantial improvement with the latter, and an improved temperature monitor is suggested. Results of dynamic circulation experiments on sample YTB-16-3 are presented. The circulation-stability experiments help to verify bubble states proposed by other workers and serve as a test of the proposed rigid-wall-structure orientation (relative to fixed laboratory axes) of bubbles in circulation. Bubble states in the other orthorhombic samples (BILY (110)) investigated were generally very unstable dynamically, but the observation of an unusually-stable state is reported. Static bubble collapse and stripe-out experiments in an applied in-plane field are discussed, which also serve as a test of the state models. An orientation preference of walls in unbiased stripe arrays and single-stripe domains in orthorhombic films is described. The effect of coercivity on single-stripe-domain orientation was observed, and the confining well field may also have had a small effect. A textbook expression for reversible M-vector rotation in a ferromagnet is extended to orthorhombic garnet films for the case in which the applied field is in the film plane. The results of a partial test of the analysis with a vibrating-sample magnetometer are described. To understand the stripe-domain orientation experiments, a numerical analysis is made of the structure of a static two-dimensional flat wall in an orthorhombic film. The numerical analysis yields both structured and unstructured azimuthal magnetization profiles. (Abstract shortened with permission of author.)

Degree

Ph.D.

Advisors

Friedlaender, Purdue University.

Subject Area

Electrical engineering

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