Spin transmission in IrMn through measurements of spin Hall magnetoresistance and spin-orbit torque

Xiao Wang, Caihua Wan, Yizhou Liu, Qiming Shao, Hao Wu, Chenyang Guo, Chi Fang, Yao Guang, Wenlong Yang, Congli He, Bingshan Tao, Xiaomin Zhang, Tianyi Ma, Jing Dong, Yu Zhang, Jiafeng Feng, Jiang Xiao, Kang L. Wang, Guoqiang Yu, and Xiufeng Han

Phys. Rev. B 101, 144412 – Published 8 April 2020

Abstract

Understanding the transport of spin current in antiferromagnetic materials is indispensable to develop antiferromagnetic spintronic devices. In this work, we study the spin current transmission through an antiferromagnetic IrMn insertion layer in a W/IrMn( $t$ )/CoFeB structure by measuring the spin Hall magnetoresistance (SMR) and spin-orbit torque (SOT). The temperature dependences of SMR and SOT effective fields indicate that the spin current transmission reaches its maximum at the Néel temperature of IrMn. The enhancement is ascribed to the increase in the interfacial spin mixing conductance, which is related to the maximum magnetic susceptibility of the IrMn layer at the Néel temperature. The spin transmission decreases monotonically as a function of the IrMn thickness, which is different from the case with an insulating antiferromagnetic NiO insertion layer in previous works. In addition, we found that the spin transmission through an antiferromagnetic IrMn layer is independent of the exchange bias orientation. Our results suggest that the spin current transmission through the IrMn layer (from W layer to CoFeB layer) is mainly mediated by spin-polarized electrons rather than magnons, which is likely due to the absence of the effective excitation of magnons in the IrMn layer by the spin-polarized current.

Received 9 February 2020
Revised 17 March 2020
Accepted 17 March 2020

DOI:https://doi.org/10.1103/PhysRevB.101.144412

Physics Subject Headings (PhySH)

Spin Hall magnetoresistance Spin-orbit coupling Spintronics

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Xiao Wang^1,2, Caihua Wan^1,2, Yizhou Liu^1,2, Qiming Shao ³, Hao Wu³, Chenyang Guo^1,2, Chi Fang^1,2, Yao Guang^1,2, Wenlong Yang^1,2, Congli He⁴, Bingshan Tao^1,5, Xiaomin Zhang^1,2, Tianyi Ma ^1,2, Jing Dong^1,2, Yu Zhang ^1,2, Jiafeng Feng^1,2, Jiang Xiao⁶, Kang L. Wang³, Guoqiang Yu ^1,2,7,*, and Xiufeng Han^1,2,7

¹Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
²Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
³Device Research Laboratory, Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
⁴Institute of Advanced Materials, Beijing Normal University, Beijing 100875, China
⁵Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China
⁶Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China
⁷Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China

^*Corresponding author: guoqiangyu@iphy.ac.cn

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Vol. 101, Iss. 14 — 1 April 2020

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Images

Figure 1
Two spin transmission mechanisms. Spin could be carried by magnon spin current ( $J_{s}^{m}$ ) and electronic spin current ( $J_{s}^{e}$ ). (a) Spin current is generated by coherent precession of the moments in CoFeB, transmitted through IrMn and injected into W layer. (b) Spin current is generated by spin Hall effect in the W layer, transmitted through IrMn and injected into CoFeB layer.
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Figure 2
(a) The schematic diagram of the longitudinal resistance measurement setup and the definition of the coordinate system and α, β, γ angles. (b) The measurement setup of the current-induced hysteresis loop shift. The perpendicular field is applied by a solenoid and the in-plane field is applied by a transverse electromagnet. (c) Three angular dependences of longitudinal resistance of the sample with a 0.25-nm IrMn layer. (d) A summary of the SMR ratio as a function of IrMn thickness at different temperatures. (e) AHE resistance loops for a W/IrMn(0.5)/CoFeB sample with currents of ±2 mA and in-plane bias field −100 Oe. (f) Current-induced effective field as a function of applied current under the opposite bias field for a W/IrMn(0.5)/CoFeB sample. (g) IrMn thickness dependence of χ, which is saturated at the relatively large in-plane field. These measurements are all performed at room temperature.
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Figure 3
(a) Temperature dependence of the SMR ratio of different samples. (b) The IrMn thickness dependence of the spin transmission enhancement peak temperatures. (c) IrMn thickness dependence of the SMR ratio at different temperatures.
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Figure 4
The dampinglike torque induced effective field obtained by in-plane angular-dependent second harmonic measurement (a) Second harmonic Hall resistance of 1.0-nm-IrMn sample at 300 K. (b) Hall resistance as a function of both out-of-plane and in-plane applied fields. (c) in-plane azimuthal angle dependence of Hall resistance with an external 10 kOe magnetic field. (d) The extracted $R_{D}$ as a function of the external in-plane magnetic field. The data are fitted to $R_{A} \frac{H_{DLT}}{| H_{ext} | - H_{K}}$ , where $R_{A}$ and $H_{K}$ are extracted from (b). (e) Temperature dependence of effective field induced by dampinglike torque. The data in (a)–(d) is from a sample with 1.0-nm IrMn at 300 K.
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Figure 5
Temperature dependence of SMR ratio (a), (c) and perpendicular exchange bias (b), (d) for the samples undergoing different field cooling process. The black data points represent the measured SMR ratio or exchange bias after the $z$ -axis field cooling. The red data points represent the measured SMR ratio or exchange bias after the $y$ -axis field cooling. The insets in (a) and (c) show the SMR ratio at temperatures of 2 ∼ 300 K. The inset in (b) shows the magnetoresistance (MR) ratio after field cooling processes in which field was applied at different azimuth angle. The MR shown here is obtained from the α dependence of longitudinal resistance.
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