Wall oscillations of domain lattices in underdamped garnet films

Abstract

This report describes a recently developed domain-wall-oscillation spectrum analyzer and the results of some sensitive quantitative measurements of domain wall motion response in underdamped garnet films. Objects of study include periodic bubble domain lattices and periodic stripe patterns. Wall displacements as small as 5 Å (only a few percent of the wall width) are detectable, thus allowing observation of resonance multiplets due to wall flexure not seen by other techniques. The data presented here are taken in the linear region at low drive (well below onset of velocity saturation) in thin film samples of Gd, Ga:YIG grown epitaxially on Gd3Ga5O12. The domain wall resonance linewidth determination of the Gilbert damping parameter agrees with monodomain ferromagnetic resonance, resolving previous discrepancies with respect to effective mass and damping coefficient found in free oscillations following pulsed excitations in thin films and in complex susceptibility spectra in thick single crystal plates. Losses and nonlinearities due to coercivity appear suppressed in dense domain configurations by the presence of strong restoring forces. Comparison of our theory and experiments show that the rigid-wall model accounts well for the first resonance, including its dependence on lattice period and external field applied normal to the film. The Döring mass, however, needs correction by numerical calculations for effects of stray fields. Empirical and a priori restoring-force coefficients agree very well with our observed resonance frequencies.