Ferromagnetic resonance of bubble garnet films with a new planar microstructure

Abstract

We report ferromagnetic resonance (FMR) of magnetic bubble films using a single loop-double loop (SLDL) planar structure with the static magnetic field applied both parallel and perpendicular to sample surfaces. Spectra were taken by direct transmission without modulation. Depending upon the positioning of the sample on the SLDL structure, two types of spectra were observed. With the sample positioned away from the coupling region (between the SL and DL conductors), transmission was decreased somewhat asymmetrically about resonance; in some cases, a weak transmission maximum occurred on the low field shoulder of an absorption line. We briefly discuss the correlation of these line shapes with a model based on a transmission line whose parameters are perturbed by the sample film’s susceptibility near resonance. The fields at transmission minima are in excellent agreement with resonance fields calculated from the Kittel equations for both the perpendicular and parallel field cases. With a film positioned to cover the SL-DL coupling region, transmission was reduced by more than one half at all fields. Resonance line shapes were sharply anomalous, evidencing strong maxima and minima similar to the derivative spectra seen in modulated FMR. In this case, transmission spectra appear to reflect a different combination of the perturbed transmission line phenomena. We conclude that resonance is not completely localized to the input-output coupling region. This sheds light on the line shapes seen by researchers with different microstructures.