Imaging Collective Magnonic Modes in 2D Arrays of Magnetic Nanoelements

We have used time resolved scanning Kerr microscopy to image collective spin wave modes within a 2D array of magnetic nanoelements. Long wavelength spin waves are confined within the array as if it was a continuous element of the same size but with effective material properties determined by the structure of the array and its constituent nanoelements. The array is an example of a magnonic metamaterial, the demonstration of which provides new opportunities within the emerging field of magnonics.

Figure 1

(a) TR signals acquired from the array are shown for different values and the history of the bias magnetic field. The “$+$” and “$-$” signs in the parenthesis correspond to the bias field approached from saturation at large positive and negative magnetic fields, respectively. (b) FFT spectra of the TR signals from (a) are shown for several values of the bias field approached from positive saturation. (c) A scanning electron microscope image of a portion of the array is shown together with the directions of the bias (${\mathbf{H}}_{\mathrm{bias}}$) and pulsed (${\mathbf{H}}_{\mathrm{pulsed}}$) magnetic fields.

Figure 2

Simulated FFT spectra of the out-of-plane component of the average dynamic magnetization of (a) an isolated nanoelement and (b) the center nanoelement within a $3\times 3$ array are shown for different values of the bias magnetic field. The inset in (a) shows simulated magnitude (top) and phase (bottom) profiles for the modes observed at the bias field of 197 Oe.

Figure 3

Simulated images of the magnitude (top) and phase (bottom) for the modes at 4.5 GHz, 4.8 GHz, and 5.4 GHz of the $3\times 3$ array are shown for a bias field of 197 Oe.

Figure 4

The FFT power spectrum calculated from the TR signal acquired from the center of the array at a bias magnetic field of 197 Oe is shown on a logarithmic scale together with the fit to a Lorentzian 3-peak function. The inset shows images of the modes confined within the entire array and corresponding to the peak frequencies identified from the fit. The darker shades of gray correspond to greater mode amplitude.