Spin transport in antiferromagnetic insulators mediated by magnetic correlations

We report a systematic study of spin transport in antiferromagnetic (AF) insulators having a wide range of ordering temperatures. Spin current is dynamically injected from ${\mathrm{Y}}_3\mathrm{F}{\mathrm{e}}_5{\mathrm{O}}_{12}$ (YIG) into various AF insulators in Pt/insulator/YIG trilayers. Robust, long-distance spin transport in the AF insulators is observed, which shows a strong correlation with the AF ordering temperatures. We find a striking linear relationship between the spin decay length in the AFs and the damping enhancement in YIG, suggesting the critical role of magnetic correlations in the AF insulators as well as at the $\mathrm{AF}/\mathrm{YIG}$ interfaces for spin transport in magnetic insulators.

Figure 1

(a) Room-temperature in-plane magnetic hysteresis loops of a $20\text{−}\mathrm{nm}$ epitaxial YIG film (blue) and a $20\text{−}\mathrm{nm}$ amorphous YIG film (red) grown on GGG, where the paramagnetic background is from the GGG substrate. Inset: Low-field hysteresis loop of the epitaxial YIG film showing a coercivity of $0.40\mathrm{Oe}$. (b) FMR derivative absorption spectra of an epitaxial (blue) and an amorphous (red) $20\text{−}\mathrm{nm}$ YIG film on GGG.

Figure 2

(a) Magnetic hysteresis loops of four $\mathrm{Py}(5\mathrm{nm})/\mathrm{AF}(20\mathrm{nm})$ bilayers at $5\mathrm{K}$ after field cooling, demonstrating a clear exchange bias in all four bilayers. Temperature dependence of $H_{\mathrm{E}}$ for the four $\mathrm{Py}(5\mathrm{nm})/\mathrm{AF}(20\mathrm{nm})$ bilayers in (b) linear and (c) $logy$ scale give the AF blocking temperature $T_{\mathrm{b}}=20,45,70$, and $330\mathrm{K}$ for $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3$, $a\text{−}\mathrm{YIG}$, $a\text{−}\mathrm{NFO}$, and NiO, respectively.

Figure 3

(a) Schematic of the ISHE measurement on various $\mathrm{Pt}/\mathrm{insulator}/\mathrm{YIG}$ structures. (b) Semilog plots of $V_{\mathrm{ISHE}}$ as a function of the insulator thickness for the six series normalized to the values for the corresponding $\mathrm{Pt}/\mathrm{YIG}$ bilayers, where the straight lines are exponential fits to each series, from which the spin decay lengths $\lambda$ are determined. (c) Details of behavior shown in (b) for insulators below $10\mathrm{nm}$.

Figure 4

(a) Frequency dependencies of FMR linewidths of a bare epitaxial YIG film, $\mathrm{SrTi}{\mathrm{O}}_3\left(20\mathrm{nm}\right)/\mathrm{YIG}$, $\mathrm{G}{\mathrm{d}}_3\mathrm{G}{\mathrm{a}}_5{\mathrm{O}}_{12}\left(20\mathrm{nm}\right)/\mathrm{YIG}$, $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3\left(20\mathrm{nm}\right)/\mathrm{YIG}$, $a\text{−}\mathrm{YIG}/\left(20\mathrm{nm}\right)/\mathrm{YIG}$, $a\text{−}\mathrm{NFO}\left(20\mathrm{nm}\right)/\mathrm{YIG}$, and $\mathrm{NiO}(20\mathrm{nm})/\mathrm{YIG}$ bilayers. (b) Excellent linear correlation between spin decay length $\lambda$ and Gilbert damping enhancement $\mathrm{\Delta }\alpha ={\alpha }_{\mathrm{insulator}/\mathrm{YIG}}\text{−}{\alpha }_{\mathrm{YIG}}$. The line is a least-squares linear fit to all data points excluding $\mathrm{SrTi}{\mathrm{O}}_3$.