Damping in Yttrium Iron Garnet Nanoscale Films Capped by Platinum

Strong damping enhancement in nm-thick yttrium iron garnet (YIG) films due to Pt capping layers was observed. This damping is substantially larger than the expected damping due to conventional spin pumping, is accompanied by a shift in the ferromagnetic resonance field, and can be suppressed by the use of a Cu spacer in between the YIG and Pt films. The data indicate that such damping may originate from the ferromagnetic ordering in Pt atomic layers near the $\mathrm{YIG}/\mathrm{Pt}$ interface and the dynamic exchange coupling between the ordered Pt spins and the spins in the YIG film.

Figure 1

(a) FMR profile for a bare YIG (25 nm) sample. (b) FMR profile for a $\mathrm{YIG}(25\mathrm{nm})/\mathrm{Pt}(20\mathrm{nm})$ sample. (c) Pt layer-caused $H_{\mathrm{FMR}}$ change as a function of the Pt thickness. The data in (a)–(c) were obtained at 9.5 GHz. (d) $\Delta H$ vs $\omega /2\pi$ responses for four samples. (e) Damping ${\alpha }_{\mathrm{eff}}$ as a function of the Pt thickness.

Figure 2

Data obtained for $\mathrm{YIG}(35\mathrm{nm})/\mathrm{Cu}/\mathrm{Pt}(23\mathrm{nm})$ (empty circles) and $\mathrm{YIG}(35\mathrm{nm})/\mathrm{Cu}$ (solid circles). (a) NM layer-caused $\Delta H$ change as a function of $d_{\mathrm{Cu}}$. (b) NM layer-caused $H_{\mathrm{FMR}}$ change as a function of $d_{\mathrm{Cu}}$. (c) Effective damping as a function of $d_{\mathrm{Cu}}$.

Figure 3

Data obtained for $\mathrm{YIG}(19\mathrm{nm})/{\mathrm{Cu}}^{*}/\mathrm{Pt}(20\mathrm{nm})$ samples as well as several control samples. (a) NM layer-caused $\Delta H$ change as a function of the Cu thickness ($d_{{\mathrm{Cu}}^{*}}$). (b) NM layer-caused $H_{\mathrm{FMR}}$ shift. (c)–(f) $\Delta H$ as a function of frequency for four samples. The open and solid circles show the data from in-plane and out-of-plane FMR measurements, respectively.

Figure 4

Atomic force microscopy surface images of three samples.