Spin Pumping in Electrodynamically Coupled Magnon-Photon Systems

We use electrical detection, in combination with microwave transmission, to investigate both resonant and nonresonant magnon-photon coupling at room temperature. Spin pumping in a dynamically coupled magnon-photon system is found to be distinctly different from previous experiments. Characteristic coupling features such as modes anticrossing, linewidth evolution, peculiar line shape, and resonance broadening are systematically measured and consistently analyzed by a theoretical model set on the foundation of classical electrodynamic coupling. Our experimental and theoretical approach paves the way for pursuing microwave coherent manipulation of pure spin current via the combination of spin pumping and magnon-photon coupling.

Figure 1

(a) Sketch of the experimental setup. The artificial $LCR$ circuit models the microwave current carried by the cavity mode, which couples with the precessing magnetization in YIG. (b) A typical cavity mode measured by transmission spectrum $|S_{21}|$. (c) The uncoupled FMR electrically detected by spin pumping. (d) $|S_{21}|$ and (e) $V(H)$ spectrum calculated by solving Eq. (1) by setting $K_c=K_m=0$.

Figure 2

Evolution of the hybrid FMR and cavity mode measured by (a) transmission spectra $|S_{21}|$ and (b) spin pumping voltage $V(H)$. Dispersion of the hybrid modes determined from (c) $|S_{21}|$ and (d) $V(H)$ spectra. Normalized linewidth of the hybrid modes determined from (e) $|S_{21}|$ and (f) $V(H)$ spectra. The solid curves in (c)–(f) are calculated by solving Eq. (1).

Figure 3

$|S_{21}|$ spectra measured (a) before and (b) after tuning the adjustable connector port of the cavity. The FMR line shape measured (c) before and (d) after tuning the connector port. (e) Comparison of the frequency dependence of the FMR linewidth measured before and after tuning the connector port. Solid curves are fits to Eq. (2).