A New Branch of the Spectrum of Single Domain Wall Excitations in Magnetic Garnet Films

180° and 90° domain walls in Bi-substituted [110] and [100] oriented garnet films with in-plane magnetization are studied by means of planar excitation-detection structures at microwave frequencies. New multiple resonance modes of single domain walls with very low linewidth (4.2 MHz) are observed at frequencies near 1 GHz. The resonances are excited by rf magnetic fields which are parallel or perpendicular to the wall plane. Resonance frequencies show a nonlinear dispersion dependence on the mode number. They decrease with an increasing static in-plane magnetic field normal to the wall plane. With decreasing film thickness the resonance frequencies increase. In addition the well known low-frequency resonances related to the wall translations or its flexural vibrations (Goldstone modes) are also observed in these samples

Spectrum of elementary excitations of a single domain wall in garnet films with in-plane magnetization

Epitaxial garnet films with in-plane magnetization are studied by microwave technique. Resonances related to different branches of domain wall excitations are observed : a low-frequency Goldstone branch of translational wall vibrations in the MHz band and a high-frequency Gilinskii branch in the GHz band. A strong coupling between neighbouring domain walls is observed, if their distance becomes comparable to the wall thichkness. In this case each resonance is split into two coupled rasonant modes, their frequencies being larger at smaller wall distances. Spin wave excitations of a single wall are analyzed by numerical solution of Landau-Lifshitz and magnetostatic equations for the case of a bulk orthorhombic ferromagnetic material. Unidirectional Gilinskii branch and asymmetric Goldstone branch are shown to exist in the spectrum of the wall excitations for the case of the propagation direction perpendicular to the magnetization in domains. Unexpected wall excitation spectra are predicted at some values of the anisotropy parameters when the wall becomes unstable. Such spectrum shows a gap in the wave number and a loop in the dispersion of the Goldstone branch