Antiferromagnonic Spin Transport from ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ into NiO

We observe highly efficient dynamic spin injection from ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (YIG) into NiO, an antiferromagnetic (AF) insulator, via strong coupling, and robust spin propagation in NiO up to 100-nm thickness mediated by its AF spin correlations. Strikingly, the insertion of a thin NiO layer between YIG and Pt significantly enhances the spin currents driven into Pt, suggesting exceptionally high spin transfer efficiency at both $\mathrm{YIG}/\mathrm{NiO}$ and $\mathrm{NiO}/\mathrm{Pt}$ interfaces. This offers a powerful platform for studying AF spin pumping and AF dynamics as well as for exploration of spin manipulation in tailored structures comprising metallic and insulating ferromagnets, antiferromagnets, and nonmagnetic materials.

Figure 1

(a) A $\theta -2\theta$ XRD scan of a 20-nm YIG epitaxial film on ${\mathrm{Gd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ (111) substrate near the YIG (444) peak. (b) A room-temperature FMR derivative absorption spectrum of a 20-nm YIG film (YIG-1) with an in-plane dc magnetic field and microwave power $P_{\text{rf}}=0.2\mathrm{mW}$; the linewidth is 8.5 Oe. AFM images of (c) a 20-nm bare YIG film and (d) a $\mathrm{YIG}/\mathrm{NiO}(20\mathrm{nm})$ bilayer over an area of $10\mu \mathrm{m}\times 10\mu \mathrm{m}$, which exhibit rms roughness of 0.197 and 0.100 nm, respectively. (e) Schematic of ISHE measurement on $\mathrm{YIG}/\mathrm{Pt}$ bilayer and $\mathrm{YIG}/\mathrm{NiO}/\mathrm{Pt}$ trilayers. (f) $V_{\mathrm{ISHE}}$ vs $H-H_{\text{res}}$ spectra at ${\theta }_H=90°$ and 270° (two opposite in-plane fields) at $P_{\text{rf}}=200\mathrm{mW}$ for a $\mathrm{YIG}\text{−}1/\mathrm{Pt}(5\mathrm{nm})$ bilayer. (g) $\theta -2\theta$ XRD scan of a 100-nm NiO film on GGG(111) substrate.

Figure 2

$V_{\mathrm{ISHE}}$ vs $H-H_{\text{res}}$ spectra of $\mathrm{YIG}(20\mathrm{nm})/\mathrm{NiO}(t_{\mathrm{NiO}})/\mathrm{Pt}(5\mathrm{nm})$ heterostructures at $P_{\text{rf}}=200\mathrm{mW}$ using (a) YIG-1, (b) YIG-2, and (c) YIG-3 with differing characteristics. The top, middle, and bottom panels are for $\mathrm{YIG}/\mathrm{Pt}$ bilayers, $\mathrm{YIG}/\mathrm{NiO}(1\mathrm{nm})/\mathrm{Pt}$, and $\mathrm{YIG}/\mathrm{NiO}(100\mathrm{nm})/\mathrm{Pt}$ trilayers, respectively.

Figure 3

Semilog plots of the NiO thickness dependencies of the ISHE voltages for $\mathrm{YIG}(20\mathrm{nm})/\mathrm{NiO}(t_{\mathrm{NiO}})/\mathrm{Pt}(5\mathrm{nm})$ trilayers using (a) YIG-1, (b) YIG-2, and (c) YIG-3. Inset: $V_{\mathrm{ISHE}}$ as a function of NiO thickness from 0 to 10 nm for the three series of samples, where the horizontal dashed lines mark the values of $V_{\mathrm{ISHE}}$ for the $\mathrm{YIG}/\mathrm{Pt}$ bilayers. (d) Semilog plot of $V_{\mathrm{ISHE}}$ as a function of the ${\mathrm{SrTiO}}_3$ barrier thickness for ${\mathrm{YIG}/\mathrm{SrTiO}}_3/\mathrm{Pt}$ trilayers. FMR linewidths as a function of NiO thickness for (e) YIG-1, (f) YIG-2, and (g) YIG-3 based trilayers, and (h) as a function of ${\mathrm{SrTiO}}_3$ thickness in ${\mathrm{YIG}/\mathrm{SrTiO}}_3/\mathrm{Pt}$ trilayers.

Figure 4

(a) Room temperature magnetic hysteresis loops of a single YIG(20 nm) film and $\mathrm{YIG}/\mathrm{NiO}$ bilayers with NiO thicknesses of 2, 5, 10, 20, and 50 nm, which give coercivities of 0.36, 0.42, 0.67, 0.93, 1.31, and 1.53 Oe, respectively. The inset shows the NiO thickness dependence of coercivity. (b) $V_{\mathrm{ISHE}}$ vs $H-H_{\text{res}}$ spectra of four heterostructures, including (1) $\mathrm{YIG}(20\mathrm{nm})/\mathrm{NiO}(5\mathrm{nm})/\mathrm{Cu}(10\mathrm{nm})/\mathrm{NiO}(5\mathrm{nm})/\mathrm{Pt}(5\mathrm{nm})$ (black), (2) $\mathrm{YIG}/\mathrm{NiO}(5\mathrm{nm})/{\mathrm{SiO}}_x(5\mathrm{nm})/\mathrm{NiO}(5\mathrm{nm})/\mathrm{Pt}(5\mathrm{nm})$ (purple), (3) $\mathrm{YIG}/\mathrm{NiO}(5\mathrm{nm})/\mathrm{Cu}(10\mathrm{nm})$ (blue), and (4) $\mathrm{YIG}/\mathrm{Cu}(10\mathrm{nm})/\mathrm{NiO}(10\mathrm{nm})/\mathrm{Pt}(5\mathrm{nm})$ (red), taken at $P_{\text{rf}}=200\mathrm{mW}$. The spectra are offset for clarity. (c) FMR derivative absorption spectra taken at $f=9.65\mathrm{GHz}$ and (d) frequency dependencies of FMR linewidth of a bare YIG-1 film, a $\mathrm{YIG}\text{−}1/\mathrm{NiO}(20\mathrm{nm})$ and a ${\mathrm{YIG}\text{−}1/\mathrm{SiO}}_x$ (20 nm) bilayer.