Spin-Wave Emission from Vortex Cores under Static Magnetic Bias Fields

We studied the influence of a static in-plane magnetic field on alternating-field-driven emission nanoscale spin waves from vortex cores. Time-resolved scanning transmission X-ray microscopy was used to image in disk structures synthetic ferrimagnets and single ferromagnetic layers. For both systems, it found that an increasing bias continuously displaces wave-emitting core center toward its edge without noticeably altering spin-wave dispersion relation. In case single-layer disk, anisotropic lateral expansion occurs at higher fields, which leads directional rather than radial-isotropic propagation waves. Micromagnetic simulations confirm these findings further show focusing effects occur such depending shape controlled by field.