Large spin pumping from epitaxial Y${}_3$Fe${}_5$O${}_{12}$ thin films to Pt and W layers

Epitaxial Y${}_3$Fe${}_5$O${}_{12}$ thin films deposited by off-axis sputtering exhibit excellent crystalline quality enabling observation of large spin pumping signals in Pt/Y${}_3$Fe${}_5$O${}_{12}$ and W/Y${}_3$Fe${}_5$O${}_{12}$ bilayers driven by cavity ferromagnetic resonance. The inverse spin Hall voltages reach 2.10 and −5.26 mV in 5-mm-long Pt/Y${}_3$Fe${}_5$O${}_{12}$ and W/Y${}_3$Fe${}_5$O${}_{12}$ bilayers, respectively, excited by a radio-frequency magnetic field of 0.3 Oe. From the ferromagnetic resonance linewidth broadening, we obtain high interfacial spin mixing conductances of 4.56×10${}^{14}$ and 2.30×10${}^{14}$ ${\Omega }^{-1}$ m${}^{-2}$ for Pt/Y${}_3$Fe${}_5$O${}_{12}$ and W/Y${}_3$Fe${}_5$O${}_{12}$ bilayers, respectively.

Figure 1

(a) Wide angle semilogarithmic θ-2θ XRD scan of a 20-nm-thick YIG film grown on GGG (111). (b) Semilogarithmic θ-2θ scans of 10-, 20-, 50-, and 80-nm-thick YIG films near the YIG (444) peak, all of which exhibit clear Laue oscillations corresponding to the film thickness. The vertical short lines mark the positions of the YIG (444) peak. The scans are offset from each other for clarity. The insets are the rocking curves of the four YIG films taken for the first satellite peak to the left of the man peak at the 2θ angle marked by the up arrows. The shoulder in the rocking curve of the 80-nm film is likely due to twinning in the film.

Figure 2

Room-temperature FMR derivative spectrum $d{I}_{\mathrm{FMR}}$/$dH$ vs $H$ of a 20-nm YIG film (YIG-1) at ${\theta }_{\mathrm{H}}$ $=$ 90° (field in-plane) gives a linewidth of 7.42 Oe. Top-right inset: FMR experimental geometry. Bottom-left inset: fit (solid green curve) to the experimental data for the angular dependence of $H_{\mathrm{res}}$ for the YIG film from which we obtain 4$\pi M_{\mathrm{eff}}$ $=$ 1794 Oe and $g$ $=$ 2.0.

Figure 3

(a) Schematic diagram of the ISHE voltage measurement setup. (b) $V_{\mathrm{ISHE}}$ vs $H$ spectra at ${\theta }_{\mathrm{H}}$ $=$ 90° and $P_{\mathrm{rf}}$ $=$ 200 mW for two Pt(5 nm)/YIG(20 nm) [Pt/YIG-1 and Pt/YIG-2] bilayers and a W(5 nm)/YIG(20 nm) [W/YIG-2] bilayer: ISHE voltages of 1.74, 2.10, and −5.26 mV, respectively, are observed. (c) Linear rf-power dependence of $V_{\mathrm{ISHE}}$ with a least-squares fit is shown for the three samples. (d) $V_{\mathrm{ISHE}}$ vs $H$ spectra at different ${\theta }_{\mathrm{H}}$ for Pt/YIG-1 and W/YIG-2. The curves are offset for clarity. The nonzero ISHE voltage at ${\theta }_{\mathrm{H}}$ $=$ 0° and the difference in $H_{\mathrm{res}}$ between Pt/YIG-1 and W/YIG-2 at the same ${\theta }_{\mathrm{H}}$ are due to slight misalignment of the sample with respect to $\mathit{H}$. (e) Angular dependence of the normalized $V_{\mathrm{ISHE}}$ for Pt/YIG-1 and W/YIG-2, where the red and blue curves show sin ${\theta }_{\mathrm{H}}$ and $-$sin ${\theta }_{\mathrm{H}}$, respectively.

Figure 4

FMR derivative absorption spectra of YIG thin films at $P_{\mathrm{rf}}$ $=$ 0.2 mW before (Δ$H_0$, blue) and after (Δ$H_f$, red) the deposition of (a) 5-nm Pt on YIG-1 ($V_{\mathrm{ISHE}}$ $=$ 1.74 mV), (b) 5-nm Pt on YIG-2 ($V_{\mathrm{ISHE}}$ $=$ 2.10 mV), and (c) 5-nm W on YIG-2 ($V_{\mathrm{ISHE}}$ $=$ 5.26 mV), which show linewidth increases from Δ$H_0$ $=$ 7.42 Oe to Δ$H_f$ $=$ 27.33 Oe, from 11.71 Oe to 36.05 Oe, and from 11.71 Oe to 24.04 Oe, respectively.