Supplemental Material
Observation of Strongly Enhanced Inverse Spin Hall Voltage in
Fe3Si/GaAs Structures
H. Y. Hung1, T. H. Chiang2, B. Z. Syu3, Y. T. Fanchiang4, J. G. Lin4, S. F. Lee5 a),
M. Hong3 a), and J. Kwo1 a)
1
Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
2
Department of Materials Science and Engineering, National Tsing Hua University,
Hsinchu 30013, Taiwan
3
Graduate Institute of Applied Physics and Department of Physics, National Taiwan
University, Taipei 10617, Taiwan
4
Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617,
Taiwan
5
Institute of Physics, Academia Sinica, Taipei 115, Taiwan
To ascertain whether the voltage signal we measured was due to the inverse spin
Hall effect (ISHE), a series of control experiments were conducted to investigate the
anisotropic magnetoresistance (AMR) effect, the spin Seebeck effect, the NernstEttingshausen effect, and the self-induced inverse spin Hall effect.1-4
(A) For the AMR effect, the Fe3Si thin film grown on semi-insulating (S.I.) GaAs (001)
substrate without an amorphous Si capping layer was measured to study the field
dependence of the voltage signal (Fig. S1) with a sample dimension of 0.7 mm 2 mm.
The signal shape of Fig. S1 showed a nearly anti-symmetric behavior, markedly
different from the signal shape of the Fe3Si/doped GaAs films. The VISHE and
VISHE/VAHE ratio of the former case were 3.6μV and 0.35, respectively. Suppose the
AMR effect is the dominant voltage signal measured for the latter sample, its VISHE is
expected be substantially smaller than 3.6μV, since we may consider the bilayer
structure by a parallel resistor model, and the doped GaAs substrate has much less
resistance than the semi-insulating GaAs. Hence the contribution of AMR effect in
VISHE of the Fe3Si/doped GaAs sample would be quite small.
(B) The spin Seebeck effect and the Nernst-Ettingshausen effect are caused by thermal
gradient in the ferromagnetic film under the resonance condition. To investigate
contributions due to these two effects, FMR measurement were performed at different
duration times of FMR. The duration times of FMR (TFMR) was defined as the FMR
line width WFe3 Si⁄GaAs (mT) divided by the sweeping rate (mT/s). Fig. S2(a) and (b)
showed the TFMR dependence of the VISHE for Fe3Si/n-GaAs(52nm) and Fe3Si/pGaAs(52nm) films. Since the magnitude of the VISHE did not change at different
sweeping rates, the VISHE should not relate to the temperature gradient under the
resonance condition. Hence the spin Seebeck effect and the Nernst-Ettingshausen effect
can be ruled out in our results.
(C) Finally, we considered the contribution of “self-induced” inverse spin Hall effect in
our experiment. The sample structure of a-Si/Fe3Si/S.I. GaAs was shown in the Fig.
S3(a) inset. A clear voltage with a VISHE of 6.5 μV and a VAHE of -3.5μV was observed
at the resonance condition under the PMW of 79 mW. According to the polarity of VISHE,
a spin current appeared to flow from Fe3Si toward the a-Si layer. In addition, the VISHE
and VAHE showed liner dependence with the increase of the microwave power (see Fig.
S3(b)). The exact cause for this apparent “self-induced” ISHE is uncertain at present,
and possible causes have been suggested.4 To determine the spin Hall angle θISHE
correctly, the self-induced VISHE should be subtracted to obtain the actual VISHE resulting
from the spin injection from Fe3Si into GaAs.
The self-induced VISHE cannot be directly estimated from the field dependence of
the voltage signal for Fe3Si/doped GaAs bilayer structure. To estimate the θISHE, we
have adopted the following procedure: First, we determined the self-induced VISHE/VAHE
ratio ~1.8 from the a-Si/Fe3Si/S.I. GaAs film. Then we assumed the same self–induced
VISHE/VAHE ratio in the Fe3Si/doped GaAs films. Hence the magnitude of the selfinduced VISHE can be estimated, and will be subtracted from the total VISHE of spin
pumping from Fe3Si to doped GaAs to obtain the modified VISHE*. In this way, the
minimum value of θISHE will be obtained without overestimating. Table S1 shows the
modified VISHE* and θISHE for n-GaAs and p-GaAs. By considering the self-induced
VISHE, the θISHE of n-GaAs and p-GaAs is now modified from the original 2.710-4 and
6.210-5 to 1.910-4 and 2.810-5, respectively.
Reference
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2.
and E. Saitoh, Nature 455, 778 (2008).
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3.
4.
107, 216604 (2011).
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Fig. S1 The field dependence of the voltage signal for Fe3Si/S.I. GaAs at the microwave
power of 100 mW.
Fig. S2 The TFMR dependence of the VISHE for Fe3Si/n-GaAs and Fe3Si/p-GaAs films at
the microwave power of 100 mW.
Fig. S3 (a) The field dependence of the voltage signal for a-Si/Fe3Si films at the
microwave power of 79 mW, and (b) the power dependence of the VISHE and VAHE.
self-induced VISHE (μV)
VISHE*(μV)
= VAHE1.8
(w/o self-induced VISHE)
VISHE
(μV)
VAHE
(μV)
n-GaAs
19.3
3.1
5.6
p-GaAs
49.2
14.8
26.6
θISHE
modified
θISHE
13.7
2.710-4
1.910-4
22.6
6.210-5
2.810-5
Table S1
The estimates of self-induced VISHE and the modified θISHE.
VISHE* = VISHE − VAHE1.8