Strong Interlayer Magnon-Magnon Coupling in Magnetic Metal-Insulator Hybrid Nanostructures

We observe strong interlayer magnon-magnon coupling in an on-chip nanomagnonic device at room temperature. Ferromagnetic nanowire arrays are integrated on a 20-nm-thick yttrium iron garnet (YIG) thin film strip. Large anticrossing gaps up to 1.58 GHz are observed between the ferromagnetic resonance of the nanowires and the in-plane standing spin waves of the YIG film. Control experiments and simulations reveal that both the interlayer exchange coupling and the dynamical dipolar coupling contribute to the observed anticrossings. The coupling strength is tunable by the magnetic configuration, allowing the coherent control of magnonic devices.

Figure 1

(a) Sketch of a hybrid magnetic nanostructure based on a YIG thin film. The applied field $H$ is in plane and parallel to the nanowires. (b) An SEM image (scale bar 500 nm) of the Ni-based nanowire array on YIG thin film. (c) Color-coded reflection spectra $S_{11}$ measured on the Ni/YIG hybrid nanostructures by a coplanar waveguide. The arrows highlight anticrossing modes induced by different in-plane standing spin-wave modes with mode numbers $n=4$, 6, 8.

Figure 2

(a) Color-coded reflection spectra $S_{11}$ for high-order ISSWs with a mode number of $n=8$. (b) The line spectrum selects the spectrum indicated by the vertical dotted line in (a) at 1200 Oe. The frequency gap in the anticrossing mode reveals the coupling strength $g$. (c) $g$ as a function of the mode number $n=4$, 6, and 8. Red dots: Experiments. Black squares: Simulations. (d) Schematic of the modeled structure. The width of YIG and Ni are 500 and 100 nm, respectively. (b) Simulation results of reflection spectra as a function of the in-plane magnetic field for the anticrossing of the Ni FMR mode and the $n=8$ ISSW YIG mode. The color represents the reflection amplitude with the scale definition on the side.

Figure 3

(a) Color-coded reflection spectra $S_{11}$ for the $n=4$ ISSW mode. (b) The line spectrum is extracted at $-450\mathrm{Oe}$. (c) Data points extracted from experimental data by reading out the maxima of each resonances. The insets depict the $n=4$ ISSW mode and the parallel state of the Co/YIG multilayer. Black dashed line: Co FMR mode. Blue dotted lines: $n=4$ ISSW modes of YIG thin film. (a)–(c) are data for $P$ states. (d)–(f) present data for the $X$ state. (g)–(i) present data for the AP state of Co/YIG hybrids [33]. All data presented in this figure are data from the $n=4$ ISSW mode.

Figure 4

Angle-dependent microwave spectra. $\theta$ is the in-plane magnetic field angle with respect to the orientation of the nanowires. At the applied field of 170 Oe, the Co wire magnetization is not modified, and the YIG magnetization is nearly parallel with the field direction. So 0° corresponds to the $P$ and 180° to the AP state. The splitting of the lines is the anticrossing between the $n=4$ ISSW mode and the Co FMR. A line plot at 180° is shown as an example of the color vs intensity code.