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Spin-Orbit Torques from Interfacial Rashba-Edelstein Effects
Axel Hoffmann Materials Science Division Argonne National Laboratory Go to "View | Header and Footer" to add your organization, sponsor, meeting name here; then, click "Apply to All"
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Chiral Symmetry breaking with Permalloy/Pt
Outline “Spin-Hall” ST-FMR Chiral Symmetry breaking with Permalloy/Pt Permalloy/MoS2 Ag/Bi Conclusions Axel Hoffmann, MSD, Argonne National Laboratory Go to "View | Header and Footer" to add your organization, sponsor, meeting name here; then, click "Apply to All"
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Spin Hall Effects are Key Enabling Phenomena
Charge + Spin Currents Spin Dynamics & Nonmagnetic Metal Ferromagnet Spin Hall Effect Spin Transfer Torque Spin Pumping inverse Spin Hall Effect Axel Hoffmann, MSD, Argonne National Laboratory
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Spin Hall Effect Driven Magnetization Dynamics
Landau-Lifshitz-Gilbert equation: damping-like field-like How can we create and detect spin currents? Axel Hoffmann, MSD, Argonne National Laboratory
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Spin-Torque Ferromagnetic Resonance
Excitation of spin dynamics by Oersted field and SHE torques. Mixing of anisotropic magnetoresistance (AMR) in Py with microwaves lead to dc rectification. Lineshape analysis can quantify spin Hall angle. L. Liu et al., Phys. Rev. Lett. 106, (2011) Axel Hoffmann, MSD, Argonne National Laboratory
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Spin-Torque Ferromagnetic Resonance
Landau–Lifshitz–Gilbert equation (LLG) τF τSTT L. Liu et al., Phys. Rev. Lett. 106, (2011)
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Chiral Symmetry Breaking in ST-FMR
Axel Hoffmann, MSD, Argonne National Laboratory
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Permalloy/Pt: Bulk vs. Interface
Spin Hall Angle: Interface: 87% Bulk: 3% L. Wang et al., Phys. Rev. Lett. 116, (2016) Axel Hoffmann, MSD, Argonne National Laboratory
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due to shape anisotropy
Coordinate system for ST-FMR Measurements with arbitrary magnetic field direction In general ψ lags θ due to shape anisotropy Axel Hoffmann, MSD, Argonne National Laboratory
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Out-of-plane FMR of Permalloy
Static equilibrium condition for FMR FMR field vs. field angle θ Axel Hoffmann, MSD, Argonne National Laboratory
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ST-FMR Permalloy/Pt in-Plane Angular Dependence
Axel Hoffmann, MSD, Argonne National Laboratory
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ST-FMR Permalloy/Pt in-Plane Angular Dependence
Axel Hoffmann, MSD, Argonne National Laboratory
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ST-FMR Dependence on Out-of-Plane Magnetic Field
Measured at 5.5 GHz, φ = 45° Axel Hoffmann, MSD, Argonne National Laboratory
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ST-FMR Dependence on Out-of-Plane Magnetic Field
Measured at 5.5 GHz, φ = 45° Axel Hoffmann, MSD, Argonne National Laboratory
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ST-FMR Dependence on Out-of-Plane Magnetic Field
Measured at 5.5 GHz, φ = 45° Axel Hoffmann, MSD, Argonne National Laboratory
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ST-FMR Dependence on Out-of-Plane Magnetic Field
Measured at 5.5 GHz, φ = 45° Axel Hoffmann, MSD, Argonne National Laboratory
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Spin Hall Effect Driven Magnetization Dynamics
Landau-Lifshitz-Gilbert equation: damping-like field-like Even in field Odd in field Axel Hoffmann, MSD, Argonne National Laboratory
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Opposite Chirality of Torques for Opposite Magnetic Fields
Normal: τF+τD rotates towards original direction of original damping–like torque Reversed: τF+τD rotates towards original direction of original field–like torque Axel Hoffmann, MSD, Argonne National Laboratory
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Dynamic Reciprocity with Pure Field-like Torque
Field reversal only results in unchanged dynamics with π-phase shift Axel Hoffmann, MSD, Argonne National Laboratory
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Dynamic Reciprocity with Pure Damping-like Torque
Field reversal results in unchanged dynamic without phase shift Axel Hoffmann, MSD, Argonne National Laboratory
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Dynamic Non-Recirpocity with Both Torques
Axel Hoffmann, MSD, Argonne National Laboratory
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Dynamic Amplitude Non-Recirpocity
Axel Hoffmann, MSD, Argonne National Laboratory
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Angular Dependence of Symmetric Voltage for “Normal” Field Configuration
Axel Hoffmann, MSD, Argonne National Laboratory
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Angular Dependence of Symmetric Voltage for “Reversed” Field Configuration
A similar result is found for the antisymmetric voltage Axel Hoffmann, MSD, Argonne National Laboratory
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Comparison Theory and Experiment “Normal”
Axel Hoffmann, MSD, Argonne National Laboratory
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Comparison Theory and Experiment “Reversed”
Axel Hoffmann, MSD, Argonne National Laboratory
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Spin Transfer Torque with 2D Materials
Axel Hoffmann, MSD, Argonne National Laboratory
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2D Semiconductors with Strong Spin-Orbit Coupling
Dichalcogenides: MoS2, MoSe2, WS2, WSe2 Rashba Spin-orbit splitting Electric field induced Zeeman splitting Are the spin-orbit torques? D. Xiao et al., Phys. Rev. Lett. 108, (2012). H. Yuan et al., Nature Phys. 9, (2013).
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Large Area monolayer MoS2 on SiO2/Si with CVD
W. Zhang et al., APL Mater. 4, (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory
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Both are indicative of single monolayer MoS2
Optical Spectra Both are indicative of single monolayer MoS2 W. Zhang et al., APL Mater. 4, (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory
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Spin Transfer Torque Measurements Py/MoS2
Any torque possibly given by the MoS2? W. Zhang et al., APL Mater. 4, (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory
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Significant Lineshape Changes
1. non-trivial Lorentzian-type signal with both symmetric and antisymmetric lineshape! 2. Angular rotation consistent with the spin torque theory. ~ cos2(f) sin(f) W. Zhang et al., APL Mater. 4, (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory
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Sizeable Torques from Interface with Monolayer!
Analytical fitting with the spin torque model using Py AMR rectification. From Rashba-effect more field like torques expected W. Zhang et al., APL Mater. 4, (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory
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MoS2 Out-of-Plane Dependence
Virtually no non-reciprocity! Mostly Damping like-torque Significant increase of torques for out-of-plane fields W. Zhang et al., APL Mater. 4, (2016) Axel Hoffmann, MSD, Argonne National Laboratory
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Ferromagnetic Resonance
Spin Torque Ferromagnetic Resonance with Ag/Bi Axel Hoffmann, MSD, Argonne National Laboratory
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Spin Pumping with Ag/Bi
Permalloy/Ag Permalloy/Bi Permalloy/Ag/Bi J. C. Rojas Sánchez et al., Nat. Comm. 4, 2944 (2013) Axel Hoffmann, MSD, Argonne National Laboratory
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Spin Pumping with Ag/Bi and Ag/Sb
W. Zhang et al., J. Appl. Phys. 117, 17C727 (2015) Axel Hoffmann, MSD, Argonne National Laboratory
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ST-FMR with Ag/Bi P = +10dBm, f = 4 GHz B. Jungfleisch et al.,
Phys. Rev. B 93, (2016) Axel Hoffmann, MSD, Argonne National Laboratory
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Gilbert Damping B. Jungfleisch et al., Phys. Rev. B 93, 224419 (2016)
Axel Hoffmann, MSD, Argonne National Laboratory
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Interfacial Damping-like Torque
B. Jungfleisch et al., Phys. Rev. B 93, (2016) Axel Hoffmann, MSD, Argonne National Laboratory
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DC Current Modulated Linewidth
8% mA-1 no effect! Axel Hoffmann, MSD, Argonne National Laboratory
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Magnetic Films Group Axel Hoffmann, Materials Science Division, Argonne National Laboratory
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Argonne National Laboratory
Thanks to Wei Zhang, Matthias B. Jungfleisch, Wanjun Jiang, Yaohua Liu, Hilal Saglam, Frank Y. Fradin, and John E. Pearson, Argonne National Laboratory Joseph Sklenar, Scott Grudichak, and John B. Ketterson Northwestern University Bo Hsu, Jiao Xiao, and Zhang Yang University of Illinois at Chicago $$$ Financial Support $$$ DOE-BES and NSF
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Conclusions Permalloy/Pt
Complete angular dependence can unambiguously identify damping- and field-like torques Presence of both results in dynamic non-reprocity Permalloy/MoS2 Relatively large spin-orbit torques Only interface / no bulk contribution! Permalloy/Ag/Bi Sufficient torque to drive magnetization dynamics Axel Hoffmann, MSD, Argonne National Laboratory
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