SpinOrbit Torques from Interfacial RashbaEdelstein Effects Axel Hoffmann

Spin-Orbit Torques from Interfacial Rashba-Edelstein Effects Axel Hoffmann Materials Science Division Argonne National Laboratory

Outline n “Spin-Hall” ST-FMR n Chiral Symmetry breaking with Permalloy/Pt n Permalloy/Mo. S 2 n Ag/Bi n Conclusions Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 2

Spin Hall Effects are Key Enabling Phenomena Charge + Spin Transfer Spin Hall Effect & Torque Currents Dynamics Spin Pumping inverse Spin Hall Effect Nonmagnetic Metal Axel Hoffmann, MSD, Argonne National Laboratory Ferromagnet hoffmann@anl. gov 3

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 hoffmann@anl. gov 4

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, 036601 (2011) Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 5

Spin-Torque Ferromagnetic Resonance Landau–Lifshitz–Gilbert equation (LLG) τSTT τF L. Liu et al. , Phys. Rev. Lett. 106, 036601 (2011)

Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 7

Permalloy/Pt: Bulk vs. Interface Spin Hall Angle: Interface: 87% Bulk: 3% L. Wang et al. , Phys. Rev. Lett. 116, 196602 (2016) Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 8

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 hoffmann@anl. gov 9

Out-of-plane FMR of Permalloy Static equilibrium condition for FMR Axel Hoffmann, MSD, Argonne National Laboratory FMR field vs. field angle θ hoffmann@anl. gov 10

ST-FMR Permalloy/Pt in-Plane Angular Dependence Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 11

ST-FMR Permalloy/Pt in-Plane Angular Dependence Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 12

ST-FMR Dependence on Out-of-Plane Magnetic Field Measured at 5. 5 GHz, φ = 45° Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 13

ST-FMR Dependence on Out-of-Plane Magnetic Field Measured at 5. 5 GHz, φ = 45° Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 14

ST-FMR Dependence on Out-of-Plane Magnetic Field Measured at 5. 5 GHz, φ = 45° Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 15

ST-FMR Dependence on Out-of-Plane Magnetic Field Measured at 5. 5 GHz, φ = 45° Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 16

Spin Hall Effect Driven Magnetization Dynamics Landau-Lifshitz-Gilbert equation: damping-like Even in field Axel Hoffmann, MSD, Argonne National Laboratory field-like Odd in field hoffmann@anl. gov 17

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 hoffmann@anl. gov 18

Dynamic Reciprocity with Pure Field-like Torque Field reversal only results in unchanged dynamics with π-phase shift Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 19

Dynamic Reciprocity with Pure Damping-like Torque Field reversal results in unchanged dynamic without phase shift Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 20

Dynamic Non-Recirpocity with Both Torques Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 21

Dynamic Amplitude Non-Recirpocity Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 22

Angular Dependence of Symmetric Voltage for “Normal” Field Configuration Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 23

Angular Dependence of Symmetric Voltage for “Reversed” Field Configuration A similar result is found for the antisymmetric voltage Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 24

Comparison Theory and Experiment “Normal” Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 25

Comparison Theory and Experiment “Reversed” Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 26

Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 27

2 D Semiconductors with Strong Spin-Orbit Coupling Dichalcogenides: Mo. S 2, Mo. Se 2, WSe 2 • Rashba Spin-orbit splitting • Electric field induced Zeeman splitting • Are the spin-orbit torques? D. Xiao et al. , Phys. Rev. Lett. 108, 196802 (2012). H. Yuan et al. , Nature Phys. 9, 563569 (2013). 28

Large Area monolayer Mo. S 2 on Si. O 2/Si with CVD 40 μm W. Zhang et al. , APL Mater. 4, 032302 (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory hoffmann@anl. gov 29

Optical Spectra Both are indicative of single monolayer Mo. S 2 W. Zhang et al. , APL Mater. 4, 032302 (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory hoffmann@anl. gov 30

Spin Transfer Torque Measurements Py/Mo. S 2 Any torque possibly given by the Mo. S 2? W. Zhang et al. , APL Mater. 4, 032302 (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory hoffmann@anl. gov 31

Significant Lineshape Changes 1. non-trivial Lorentzian-type signal with both symmetric and antisymmetric lineshape! 2. Angular rotation consistent with the spin torque theory. ~ cos 2(f) sin(f) W. Zhang et al. , APL Mater. 4, 032302 (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory hoffmann@anl. gov 32

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, 032302 (2016) Axel Hoffmann, Materials Science Division, Argonne National Laboratory hoffmann@anl. gov 33

Mo. S 2 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, 032302 (2016) Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 34

Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 35

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 hoffmann@anl. gov 36

Spin Pumping with Ag/Bi and Ag/Sb W. Zhang et al. , J. Appl. Phys. 117, 17 C 727 (2015) Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 37

ST-FMR with Ag/Bi P = +10 d. Bm, f = 4 GHz B. Jungfleisch et al. , Phys. Rev. B 93, 224419 (2016) Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 38

Gilbert Damping B. Jungfleisch et al. , Phys. Rev. B 93, 224419 (2016) Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 39

Interfacial Damping-like Torque B. Jungfleisch et al. , Phys. Rev. B 93, 224419 (2016) Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 40

DC Current Modulated Linewidth 8% m. A-1 no effect! Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 41

Magnetic Films Group Axel Hoffmann, Materials Science Division, Argonne National Laboratory hoffmann@anl. gov 42

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 43

Conclusions n Permalloy/Pt – Complete angular dependence can unambiguously identify damping- and field-like torques – Presence of both results in dynamic non-reprocity n Permalloy/Mo. S 2 - Relatively large spin-orbit torques - Only interface / no bulk contribution! n Permalloy/Ag/Bi - Sufficient torque to drive magnetization dynamics Axel Hoffmann, MSD, Argonne National Laboratory hoffmann@anl. gov 44