Fig. 1: Broadband spin-wave spectroscopy and X-ray photoemission electron microscopy (XPEEM) study of artificial magnetic quasicrystals (AMQs).
a Sketch of broadband spin-wave spectroscopy showing the two ports, P1 and P2, of a vector network analyzer (VNA) connected to a coplanar waveguide via microwave probes. Scanning electron microscopy (SEM) images showing 3rd generation Penrose P3 lattices: b P3A for which nanobars are fully connected, c P3B with partially connected nanobars, and d P3C with disconnected nanobars. The scale bars correspond to 1 μm. The Type I, Type II, and Type III nanobars are indicated by blue, green and red colored lines, respectively, in (b). The scale bars correspond to 1 μm. Gray-scale spin-wave spectra obtained on 8th generation (e) P3A, (f) P3B, and (g) P3C samples. The magnetic field was applied along the horizontal direction of graphs (b)–(d) and varied from +90 mT to −90 mT in a step-wise manner. In the field regime between the blue arrows (e) the reversal of the AMQ takes place. The magenta color arrows mark H = 0 in (e). The green arrow in (g) marks the high-frequency mode in the reversal regime. The yellow arrow highlights the branch attributed to nanomagnets being almost perpendicular to the applied field. h Sketch of the XPEEM imaging experiment performed on ferromagnetic quasicrystals. Here a Penrose P2 tiling is shown as an SEM image. D and w represent the length and width of a nanobar, respectively. XPEEM topography images of nanobars arranged on Penrose P2 lattices (i) P2A, (j) P2B, and (k) P2C. XPEEM X-ray magnetic circular dichroism (XMCD) images taken on (l) P2A, (m) P2B, and (n) P2C. Analysis of the magnetic configurations of vertices based on the charge (Q) model for (o) P2A, (p) P2B, and (q) P2C. The magnitude of Q is given by diameter and intensity of circles (legend). Orange (green) color indicates negative (positive) charge. The broken lines guide the eye for the allocation of charges to a specific vertex. For the configurations shown the maximum evaluated ∣Q∣ amounted to 3. The XPEEM images were taken at μ0H = 0 mT after applying μ0H = −52 mT such that H had pointed in −x-direction. The bright (dark) regions in (h) represent Py (Si substrate).
