MAGNETOELASTIC EFFECTS ASSOCIATED WITH SURFACE ACOUSTIC WAVE PROPAGATION IN MAGNETIC BUBBLE GARNET FILMS
Abstract
Through the magnetoelastic coupling in a magnetic film, the propagation characteristics of a Surface Acoustic Wave (SAW) can be controlled by an externally applied magnetic field. Thus, magnetic films can offer a means for tuning the SAW devices. Also, by analyzing the magnetic field dependence of the detected SAW signal, some of the magnetic characteristics of the magnetic film can be probed. This thesis deals with the first systematic experimental investigation of the magnetoelastic effects associated with the propagation of SAW in magnetic bubble garnet films. Typically, these are epitaxially grown films with substantial perpendicular uniaxial anisotropy. SAW propagation in such films has not been investigated extensively. In the investigation reported in this thesis, SAW delay lines using ZnO/garnet layered structure have been fabricated. Amplitude and phase delay variations of the SAW delayed signal were measured as a function of an externally applied dc magnetic field. The results obtained show that the phase velocity of the SAW propagating in a magnetic film can be changed by an externally applied magnetic field. The orientation of this field with respect to both the SAW propagation direction and the crystallographic directions of the magnetic film was found to be an important factor. In the film plane the angular dependence of the bias magnetic field required for maximum magnetoelastic resonance coupling was found to have a six-fold symmetry in the (111)-film plane. The change in phase was found to be accompanied by, generally, a small increase in the SAW attenuation. The magnetic field dependence of the change in the phase velocity was explained by a theoretical analysis using the ferromagnetic resonance (FMR) model. The increase in the SAW attenuation is attributed to the magnetic damping that accompanies the precession of the magnetic moments. The potential for a practical application for observed magnetoelastic effects was demonstrated by implementing a magnetically tunable SAW oscillator using a magnetic bubble film.
Degree
Ph.D.
Subject Area
Condensation
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