Abstract
We studied the influence of a static in-plane magnetic field on the alternating-field-driven emission of nanoscale spin waves from magnetic vortex cores. Time-resolved scanning transmission X-ray microscopy was used to image spin waves in disk structures of synthetic ferrimagnets and single ferromagnetic layers. For both systems, it was found that an increasing magnetic bias field continuously displaces the wave-emitting vortex core from the center of the disk toward its edge without noticeably altering the spin-wave dispersion relation. In the case of the single-layer disk, an anisotropic lateral expansion of the core occurs at higher magnetic fields, which leads to a directional rather than radial-isotropic emission and propagation of waves. Micromagnetic simulations confirm these findings and further show that focusing effects occur in such systems, depending on the shape of the core and controlled by the static magnetic bias field.
Highlights
Spin waves, and their magnon quasiparticles, are the collective elementary excitations of ordered spin systems
The mechanism behind this emission of short-wavelength spin waves lies in the strongly enhanced local effective magnetic fields and, torques that are present near the vortex core, which couple to the spin-wave continuum
We have demonstrated with direct time-resolved scanning transmission X-ray microscopy (TR-STXM) imaging that a static in-plane magnetic bias field can be used to continuously displace the position of vortex core spin-wave emitters
Summary
Their magnon quasiparticles, are the collective elementary excitations of ordered spin systems. In a classical view of a spin wave, magnetic moments precess with a periodic spatial phase shift that determines the wavelength of the excitation (Figure 1a).[1,2] The research on spin waves ranges from fundamental physics like Bose−Einstein condensates[3,4] to proposed applications in, for example, logic operations.[5,6] The utilization of spin waves for devices has two main advantages over present charge-based microelectronic technologies: the first is a low power consumption, because when spin waves are used as signal carriers electric charges are not necessarily displaced, which means that ohmic losses can be prevented. This property provides a high potential for the development of miniature signal processing devices
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