Self-induced inverse spin Hall effect in permalloy at room temperature

Ayaka Tsukahara, Yuichiro Ando, Yuta Kitamura, Hiroyuki Emoto, Eiji Shikoh, Michael P. Delmo, Teruya Shinjo, and Masashi Shiraishi

Phys. Rev. B 89, 235317 – Published 24 June 2014

Abstract

Inverse spin Hall effect (ISHE) allows the conversion of pure spin current into charge current in nonmagnetic materials due to spin-orbit interaction (SOI). In ferromagnetic materials (FMs), SOI is known to contribute to anomalous Hall effect, anisotropic magnetoresistance, and other spin-dependent transport phenomena. However, SOI in FM has been ignored in ISHE studies in spintronic devices, and the possibility of “self-induced ISHE” in FM has never been explored until now. In this paper, we demonstrate the experimental verification of ISHE in FM. We found that the spin-pumping-induced spin current in permalloy (Py) film generates a transverse electromotive force (EMF) in the film itself, which results from the coupling of spin current and SOI in Py. The control experiments ruled out spin rectification effect and anomalous Nernst effect as the origin of the EMF.

Received 30 September 2013
Revised 4 June 2014

DOI:https://doi.org/10.1103/PhysRevB.89.235317

Authors & Affiliations

Ayaka Tsukahara^1,*, Yuichiro Ando^1,2,*, Yuta Kitamura^1,*, Hiroyuki Emoto¹, Eiji Shikoh^1,†, Michael P. Delmo^1,‡, Teruya Shinjo^1,2, and Masashi Shiraishi^1,2,§

¹Graduate School of Engineering Science, Osaka University, Toyonaka 560-8531, Japan
²Graduate School of Engineering, Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8530, Japan

^*These authors contributed equally to this study.
^†Present address: Department of Engineering, Osaka City University, Osaka 558-8585, Japan.
^‡Present address: Physics Department, De La Salle University, Manila 0922, Philippines.
^§Corresponding author: mshiraishi@kuee.kyoto-u.ac.jp

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Vol. 89, Iss. 23 — 15 June 2014

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Figure 1
(a) A schematic illustration of the devices. The dimensions of the Ni $_{80}$ Fe $_{20}$ (Py) layer are 1.5 mm ( $l$ ) × 4.0 mm and the thickness, $d$ , is 10 nm. Two electrodes are attached on the Py layer using Ag paste. Electrode separation width, $w$ , is 2.5 mm. The static external magnetic field, $H$ , is applied at an angle of $θ_{H}$ to the Py film plane. (b) FMR spectra, $d I (H) / d H$ , of the Py/SiO $_{2}$ device for $θ_{H}$ = 0°, as a function of $H$ - $H_{FMR}$ , where $I$ is microwave absorption intensity in arbitrary units. The microwave power is 200 mW, and the ferromagnetic resonance field, $H_{FMR}$ , and peak-to-peak width, Δ $W$ , of the FMR signal are estimated to be 115.6 and 7.8 mT, respectively. (c) The $H$ dependences of the electromotive force (EMF), $V_{y}$ , for $θ_{H}$ = 0°. (d) $θ_{H}$ dependence of the $V_{ISHE}$ . The microwave power is 200 mW. Background signals are subtracted from the raw data by taking an average of the signals at $θ_{H}$ = 0° and 180°, and so on. (e) Microwave power, $P_{MW}$ , dependence of the $V_{ISHE}$ and the $V_{AHE}$ , where the $V_{ISHE}$ and $V_{AHE}$ are the amplitudes of the electromotive forces due to the ISHE and the AHE, respectively. The red and blue solid lines are results of linear fitting of the experimental data. The inset shows $H$ dependence of the $V_{y}$ under different microwave excitation powers when $θ_{H}$ = 0°.
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Figure 2
(a) The $H$ dependence of $d I (H) / d H$ , when $θ_{H}$ = 0° for the Py/YIG sample (solid line). The FMR signal for the Py/SiO $_{2}$ sample is also displayed as a black broken line. The procedures of the measurements of the EMFs and the geometry of the sample are the same as those of the Py/SiO $_{2}$ sample. $H_{FMR}$ and Δ $W$ are estimated to be 107.3 and 3.4 mT, respectively. The $H$ dependence of the electromotive force, $V_{y}$ , measured for Py/YIG, when $θ_{H}$ = 0°. The open circles are the experimental data and the red and blue solid lines are the contribution from the ISHE and the AHE, respectively. The notable point is that the EMF by the ISHE from this sample is quite small and the $V_{ISHE}$ was estimated to be 2.7 μV.
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Figure 3
(a) A schematic illustration of the samples for measurement of the SRE due to the AMR. (b) Typical $V_{x}$ - $H$ curves for the Py/SiO $_{2}$ and Py/YIG samples. The microwave power is 200 mW. $θ_{H}$ dependence of the $V_{AMR}$ for the (c) Py/SiO $_{2}$ and (d) Py/YIG samples. (e) Theoretically calculated $V_{AMR}$ as a function of $θ_{H}$ . The fitting parameters are α = 0.0096, $M_{s}$ = 71.9 mT, φ = 0.175, $h_{rf}$ = 0.06 mT, $f$ = 9.622 GHz, γ = 1.86 × 10 $^{11}$ T $^{- 1}$ s $^{- 1}$ , $ρ_{A}$ = 7.24 × 10 $^{- 9}$ $Ω$ m, and the current density for $V_{AMR}$ was set to be 1.1 × 10 $^{9}$ A/m $^{2}$ .
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Figure 4
$θ_{H}$ dependence of the $V_{ISHE}$ for (a) Py/SiO $_{2}$ and (b) Py/YIG samples. The microwave power is 200 mW. Theoretically calculated (c) $V_{PHE}$ and (d) $V_{ISHE}$ as a function of θ $_{H}$ . V $_{PHE}$ + $V_{ISHE}$ as a function of $θ_{H}$ , where the magnitudes of $V_{ISHE}$ are (e) 6 and (f) 19 μV. The fitting parametersare α = 0.0096, $M_{s}$ = 71.9 mT, φ = 0.175, $h_{rf}$ = 0.06 mT, $f$ = 9.622 GHz, γ = 1.86 × 10 $^{11}$ T $^{- 1}$ s $^{- 1}$ , $ρ_{A}$ = 7.24 × 10 $^{- 9}$ Ω m, and the current density for $V_{PHE}$ was set to be 2.2 × 10 $^{10}$ A/m $^{2}$ .
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Figure 5
(a) A schematic illustration of the Py/SiO $_{2}$ sample for Hall effect measurement. The dimensions of the Py layer were 60 × 700 μm $^{2}$ and the thickness, $d$ , was set to be 50 nm. A dc current, $I_{x}$ , of 1 mA and a perpendicular magnetic field, $H$ , are applied. (b) The $H$ dependence of the Hall voltage of the Py/SiO $_{2}$ sample. The linear relationship between the Hall voltages and the | $H$ | above 1 T is reasonably explained by the normal Hall effect and the red line is a linear fit of the data at $|H| > 1$ T. The anomalous Hall voltage of the Py layer is obtained from the ordinate intercept of the fitting line.
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