Electrical detection of direct and alternating spin current injected from a ferromagnetic insulator into a ferromagnetic metal

We report dual spin pumping in magnetic bilayers made of a ferromagnetic insulator yttrium iron garnet (YIG) and a ferromagnetic metal permalloy (Py). At the YIG ferromagnetic resonance (FMR), we detect a charge voltage in Py caused by YIG spin pumping. At the Py FMR, we measure the charge voltage generated by Py spin rectification. A striking simultaneous enhancement of both voltages is found at the equal resonance condition of both FMRs, which we attribute to dynamic coupling of the dual spin pumping. Our results demonstrate that Py enables electrical detection of both dc and ac spin currents in the spin pumping from YIG, which reveals an alternative path for developing insulator spintronics.

Figure 1

The FMR of (a) Py and (b) YIG can be detected by measuring $V_{SR}$ via the spin rectification effect, and $V_{SP}$ via the spin pumping effect, respectively. (c) At the equal-resonance condition, the ac spin current pumped from the YIG enhances the FMR of Py, which can be detected by the increased $V_{SR}$. Correspondingly, enhanced YIG FMR can be detected via the increased $V_{SP}$.

Figure 2

(a) The YIG and (b) the Py FMR electrically detected via $V_{SP}$ at $\varphi ={90}^{\circ }$ and $V_{SR}$ at $\varphi =0^{\circ }$, respectively. (c) The field dispersions of the Py and YIG FMRs measured at in-plane ($\theta =$ 90${}^{\circ }$) and out-of-plane ($\theta \approx$ 0${}^{\circ }$) field configurations. Curves are calculated theoretically.

Figure 3

(a) YIG and (b) Py FMR measured at $\omega /2\pi =$ 7 GHz near $\theta ={12}^{\circ }$. (c) The polar angular dependence of the resonance fields showing the Py FMR crossing the YIG resonances at $\theta =$ 12${}^{\circ }$ and 14${}^{\circ }$. The normalized amplitudes of (d) the Py and (e) the YIG FMR voltages showing the simultaneous enhancement at equal-resonance conditions. Solid curves in (a) and (b) are from fitting, solid curves in (c), (d), and (e) are calculated theoretically, dashed curves in (d) and (e) are a guide to eyes.

Figure 4

The polar angular dependence of the YIG and Py FMRs measured at $\omega /2\pi =$ 7 GHz and $\varphi ={45}^{\circ }$ on samples with Py thickness of (a) 10 and (b) 30 nm. Solid and dashed curves are from the fitting of the YIG and Py FMR, respectively.