Giant spin Hall angle in the Heusler alloy Weyl ferromagnet ${\mathrm{Co}}_{2}\mathrm{MnGa}$

Letter

Giant spin Hall angle in the Heusler alloy Weyl ferromagnet ${Co}_{2} MnGa$

L. Leiva, S. Granville, Y. Zhang, S. Dushenko, E. Shigematsu, T. Shinjo, R. Ohshima, Y. Ando, and M. Shiraishi

Phys. Rev. B 103, L041114 – Published 29 January 2021

Abstract

Weyl semimetals are playing a major role in condensed-matter physics due to exotic topological properties, and their coexistence with ferromagnetism may lead to enhanced spin-related phenomena. Here, the inverse spin Hall effect (ISHE) in the ferromagnetic Weyl semimetal Heusler alloy ${Co}_{2} MnGa$ was investigated at room temperature by means of electrical spin injection in lateral spin valve structures. Spin transport properties such as spin polarization and spin diffusion length in this material were precisely extracted in order to estimate the spin Hall angle $θ_{SH}$ , which was found to be $- 0.19 \pm 0.04$ and is among the highest reported for a ferromagnet. Although this value is on the same order of magnitude of known heavy metals, the significantly higher resistivity of ${Co}_{2} MnGa$ implies an improvement on the magnitude of detection voltages, while its ferromagnetic nature allows controlling the intensity of SHE through the magnetization direction. It was also shown that Onsager's reciprocity does not hold for this system, which is in part attributable to a different spin-dependent Hall conductivity for spin-up and spin-down carriers.

Received 28 August 2020
Accepted 8 January 2021

DOI:https://doi.org/10.1103/PhysRevB.103.L041114

Physics Subject Headings (PhySH)

Inverse spin Hall effect Spin current

Heusler alloy Weyl semimetal

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

L. Leiva ¹, S. Granville^2,3, Y. Zhang ^2,3, S. Dushenko ^1,4,5, E. Shigematsu¹, T. Shinjo¹, R. Ohshima¹, Y. Ando¹, and M. Shiraishi ¹

¹Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan
²Robinson Research Institute, Victoria University of Wellington, Wellington 6140, New Zealand
³The MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6011, New Zealand
⁴Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA
⁵Physical Measurements Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA

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Vol. 103, Iss. 4 — 15 January 2021

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Figure 1
(a) XRD pattern obtained for an out-of-plane $θ - 2 θ$ scan of a sample consisting of a 30-nm-thick ${Co}_{2} MnGa$ film grown on a single-crystal MgO substrate. Only the reflections due to the main x-ray source (Co $K_{α}$ ) are indexed. The inset shows the rocking curve for the (111) peak. (b) Scanning electron microscope (SEM) image of a two-wire LSV. In an ISHE/SHE measurement, the magnetic field $H$ is applied parallel to the copper channel (color shown for clarity). (c) SEM image of a close view of the electrodes in a LSV with an absorption middle wire (color shown for clarity). (d) Schematics of the nonlocal ISHE measurement. A charge current $I_{c}$ is injected from $F 1$ to $N$ , producing spin accumulation at the $F 1 / N$ interface, and a consequent spin current $I_{s}$ diffuses along $N$ . Part of this spin current is absorbed by the detector $D$ in the negative $z$ direction. Then, a charge current in the positive $y$ direction is induced in $D$ due to the inverse spin Hall effect, and a voltage can be measured in the equilibrium open-circuit condition.
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Figure 2
(a) Schematics of the ISHE setup for a ferromagnetic detector. In this kind of sample both FM electrodes are made of the same material, either ${Co}_{2} MnGa$ or Py. For the SHE setup, the current source and voltmeter are exchanged, preserving the polarity. (b) Schematics of the ISHE setup for a nonmagnetic detector. In this case Py was used for FM electrodes, but one of them is not used in this measurement. The SHE setup is obtained by exchanging the current source with the voltmeter while preserving the polarity. (c) Nonlocal resistance of the ISHE setup and of its reciprocal (direct) SHE setup for ${Co}_{2} MnGa$ , measured as a function of in-plane external magnetic field $H$ at room temperature. The bottom panel shows a typical AMR curve for ${Co}_{2} MnGa$ electrode $F 1$ . (d) Equivalent nonlocal ISHE and SHE resistances measured for Pt and Py at room temperature. The bottom panel shows the AMR curve for electrode $F 1$ made of Py in both cases.
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Figure 3
(a) Channel length dependence of the nonlocal signal measured for several LSV devices at room temperature. The inset shows how $Δ R_{NL4T}$ is determined in an example of the acquired spin signal as a function of in-plane longitudinal magnetic field. (b) Hanle effect nonlocal signal as a function of the external out-of-plane magnetic field for two different channel lengths. A simultaneous fitting with common parameters is shown by the solid red line. In both panels, insets show a schematic of the measurement setup in each case.
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Figure 4
Data for $- 2 α_{F} t_{F} Δ R_{ISHE} / (1 - α_{F}^{2}) W_{N} x$ as a function of $Δ R_{NL4T}$ obtained for ${Co}_{2} MnGa$ at room temperature for several devices. The spin Hall angle can be obtained from the slope of the linear fitting. Data points correspond to devices with different channel lengths $L$ .
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Figure 5
Anomalous Hall resistance for ${Co}_{2} MnGa$ (top) and Py (bottom) measured at room temperature. The inset in the bottom panel shows a schematic of the measurement setup, where the magnetic field is applied out of plane in a Hall bar structure.
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Physical Review B

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Giant spin Hall angle in the Heusler alloy Weyl ferromagnet ${Co}_{2} MnGa$

L. Leiva, S. Granville, Y. Zhang, S. Dushenko, E. Shigematsu, T. Shinjo, R. Ohshima, Y. Ando, and M. Shiraishi

Phys. Rev. B 103, L041114 – Published 29 January 2021

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Physical Review B

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Giant spin Hall angle in the Heusler alloy Weyl ferromagnet Co2MnGa

L. Leiva, S. Granville, Y. Zhang, S. Dushenko, E. Shigematsu, T. Shinjo, R. Ohshima, Y. Ando, and M. Shiraishi

Phys. Rev. B 103, L041114 – Published 29 January 2021

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Giant spin Hall angle in the Heusler alloy Weyl ferromagnet ${Co}_{2} MnGa$