Burst-mode manipulation of magnonic vortex crystals

The manipulation of polarization states in $4\times 4$ vortex crystals using sinusoidal magnetic field bursts is investigated by means of a broadband ferromagnetic-resonance setup. Magnetic field excitation with the proper amplitude and frequency allows tuning different polarization states, which are observed in the measured absorption spectra. The variation of the sinusoidal burst width consecutively identifies the time scale of the underlying process. A memorylike polarization state writing process is demonstrated on the submicrosecond time scale.

Figure 1

(a) Polarization patterns of the $4\times 4$ vortex crystal obtained from scanning transmission x-ray microscopy for two different state-formation frequencies. The region of the magnetic vortex core is shown. The polarizations are depicted by black ($p=-1$) and white ($p=1$) contrast. (b) Sinusoidal magnetic field burst with defined burst width, amplitude, and frequency (80 ns, 1.3 mT, and 190 MHz in the example). (c) Ground-signal-ground geometry of the waveguide on top of the arrays of ferromagnetic disks. The inset shows a $4\times 4$ array of the disks. (d) Scheme of the investigated $4\times 4$ vortex crystal.

Figure 2

(a), (b) Absorption spectra of the ensemble of arrays of $4\times 4$ magnetic vortices after the application of a sinusoidal magnetic field burst with a width of 5 $\mu \mathrm{s}$. The burst amplitude is varied. The frequency of the applied field is (a) 190 MHz and (b) 260 MHz. Calculated absorption spectra for the two frequencies (c) 190 MHz and (d) 260 MHz. The spectra are calculated from the ensemble of all stable states for different burst amplitudes.

Figure 3

Absorption spectra of the ensemble of arrays of $4\times 4$ magnetic vortices for a constant burst amplitude of (a) 500 A/m and (b) 1200 A/m, in dependence on the burst width. The frequency of the sinusoidal field burst is (a) 190 MHz and (b) 260 MHz. The red line indicates a smoothed fit to the maximum of the absorption to guide the eye. The time scale of the polarization state formation is about 100 ns.

Figure 4

(a) Absorption spectra of the writing process between two polarization states over time. (b) Absorptions at the indicated frequencies of the absorption spectra (red and blue). The writing bursts are indicated by light blue and light red regions. They have frequencies of (1) 180 MHz and (2) 260 MHz and a length of 200 ns. The burst amplitude is (1) 500 A/m and (2) 1250 A/m. The writing process is independent of the prior polarization state.