Spin-Pump-Induced Spin Transport in $p$-Type Si at Room Temperature

A spin battery concept is applied for the dynamical generation of pure spin current and spin transport in $p$-type silicon ($p$-Si). Ferromagnetic resonance and effective $s\mathrm{\text{−}}d$ coupling in ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ results in spin accumulation at the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/p$-Si interface, inducing spin injection and the generation of spin current in the $p$-Si. The pure spin current is converted to a charge current by the inverse spin Hall effect of Pd evaporated onto the $p$-Si. This approach demonstrates the generation and transport of pure spin current in $p$-Si at room temperature.

Figure 1

(a) A schematic illustration of spin-pumping-induced spin current generation in $p$-Si (substrate) and the conversion of spin current to charge current in a paramagnetic Pd wire due to the inverse spin-Hall effect (ISHE) [7]. In the FMR condition of the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ (Py) film, the dynamical exchange interaction drives the spin pumping, spin propagation in the $p$-Si, and absorption of pure spin currents into the Pd. (b) A schematic illustration of the sample, consisting of a Py film and a Pd wire on a $p$-Si substrate. $L$ is the gap length between the Py film and the Pd wire. (c) An optical microscope image of a part of the sample surface.

Figure 2

(a) A schematic illustration of an ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ (Py) film sample on an ${\mathrm{SiO}}_2$ substrate. (b) The external magnetic field $H$ dependence of the FMR signals $dI(H)/dH$ measured for the $\mathrm{Py}/{\mathrm{SiO}}_2$ sample (a black line) and for the $\mathrm{Py}/\mathrm{p}$-$\mathrm{Si}/\mathrm{Pd}$ sample (a red line) shown in Fig. 2c when $H$ was applied parallel to the film plane. Here, $I$ denotes the microwave absorption intensity, and the definition of the spectral width $W$ is shown in the inset of the figure. (c) A schematic illustration of the sample consisting of a Py film and a Pd wire on a $p$-Si substrate, with the definition of the magnetic field angle ${\theta }_{\mathrm{H}}$ and the Py magnetization-orientation angle ${\theta }_{\mathrm{M}}$. (d) $H$ dependence of the electromotive force $V$ measured for the $\mathrm{Py}/\mathrm{p}$-$\mathrm{Si}/\mathrm{Pd}$ sample at ${\theta }_{\mathrm{H}}=0°$. The open circles are the experimental data, and the blue solid line shows the fitting results based on Eq. (1).

Figure 3

(a) ${\theta }_{\mathrm{H}}$ dependence of the FMR signals $dI(H)/dH$ measured for the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}(\mathrm{Py})/p\mathrm{\text{−}}\mathrm{Si}/\mathrm{Pd}$ sample. $H_{\mathrm{FMR}}$ was 131 mT at ${\theta }_{\mathrm{H}}=0°$, 1142 mT at ${\theta }_{\mathrm{H}}=90°$, and 130 mT at ${\theta }_{\mathrm{H}}=180°$. (b) ${\theta }_{\mathrm{H}}$ dependence of the electromotive force $V({\theta }_H)$ measured for the $\mathrm{Py}/p$-$\mathrm{Si}/\mathrm{Pd}$ sample. The open circles are the experimental data and the solid lines show fitting results based on Eq. (1). (c) ${\theta }_{\mathrm{H}}$ dependence of the electromotive force $V$ normalized by the $V$ value at ${\theta }_{\mathrm{H}}=0°$. (d) ${\theta }_{\mathrm{M}}$ dependence of the electromotive force $V$ normalized by the $V$ value at ${\theta }_{\mathrm{M}}=0°$. The dashed line is a fitting curve proportional to $\cos {\theta }_{\mathrm{M}}$.

Figure 4

(a) A schematic illustration of the ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}(\mathrm{Py})/p\mathrm{\text{−}}\mathrm{Si}/\mathrm{Pd}$&Cu sample, and the definition of the magnetic field angle ${\theta }_{\mathrm{H}}$. $L$ is the gap length between the Py film and the Pd or Cu wire. (b) ${\theta }_{\mathrm{H}}$ dependence of the electromotive force $V({\theta }_{\mathrm{H}})$ in the Pd wire (purple circles), and that in the Cu wire (green circles) of the $\mathrm{Py}/p\mathrm{\text{−}}\mathrm{Si}/\mathrm{Pd}$&Cu sample.