Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E38: Spin-Orbit TorquesFocus Live
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Sponsoring Units: GMAG DMP FIAP Chair: Rahul Mishra, Indian Institute of Technology Delhi |
Tuesday, March 16, 2021 8:00AM - 8:36AM Live |
E38.00001: Magnetic tunnel junctions and magnetic logic circuits driven by spin-orbit torques Invited Speaker: Pietro Gambardella Current-induced spin-orbit torques (SOTs) enable the switching of magnetic tunnel junctions (MTJs) in nonvolatile magnetic random access memories as well as the all-electrical operation of magnetic logic circuits based on domain wall manipulation. This talk will present time-resolved measurements of magnetization reversal driven by SOTs in 3-terminal MTJ devices and show how the combination of SOT, spin transfer torque, and voltage control of magnetic anisotropy leads to reproducible sub-ns magnetization reversal with a very narrow spread of the switching time distributions [1, 2]. Further, it will be shown how SOTs and the chiral coupling between neighbouring magnetic domains induced by the interfacial Dzyaloshinskii–Moriya interaction [3] allow for realizing an electrically-driven domain-wall inverter. Starting from this basic building block, it is possible to fabricate reconfigurable NAND and NOR logic gates, and therefore a complete family of logic gates, which perform operations with current-induced domain-wall motion [4]. Opportunities for scalable all-electric magnetic memories and memory-in-logic applications will be discussed. |
Tuesday, March 16, 2021 8:36AM - 8:48AM Live |
E38.00002: Deterministic switching of a perpendicularly polarized magnet using unconventional spin-orbit torques in WTe2 I hsuan Kao, Ryan Muzzio, Hantao Zhang, Menglin Zhu, Jacob Giovanni Gobbo, Daniel Weber, Rahul Rao, Jiahan Li, James Edgar, Joshua Goldberger, Jiaqiang Yan, David George Mandrus, Jinwoo Hwang, Ran Cheng, Jyoti Kotach, Simranjeet Singh Spin-orbit torque (SOT) driven deterministic control of the magnetization state of a magnet with perpendicular magnetic anisotropy is key to next generation spintronic applications including non-volatile, ultrafast, and energy efficient data storage devices1-3. But field-free deterministic switching of perpendicular magnetization remains a challenge because it requires an out-of-plane anti-damping torque, which is not allowed in conventional spin source materials such as heavy metals1-3 and topological insulators4 due to system symmetry. The exploitation of low-crystal symmetries in emergent quantum materials offers a unique approach to achieve spin-orbit torque with unconventional form5,6. Here, we report the first experimental realization of field-free deterministic magnetic switching of a perpendicularly polarized van der Waals (vdW) magnet employing an out-of-plane anti-damping SOT generated in layered WTe2 which is a low-crystal symmetry quantum material. |
Tuesday, March 16, 2021 8:48AM - 9:00AM Live |
E38.00003: Effect of interfacial intermixing on spin-orbit torque in Co/Pt bilayers Giovanni Baez Flores, Kirill Belashchenko Using the first-principles non-equilibrium Green’s function technique [1] with supercell disorder averaging, we study the influence of interfacial intermixing on the spin-orbit torque in Co/Pt (111) bilayers. The interlayer distances are optimized, several models of intermixing are considered, and atomic potentials in the intermixed layers are obtained using the coherent potential approximation. The magnitude and thickness dependence of the damping-like torque are similar to earlier results for the Co/Pt (001) interface [1,2] and rather insensitive to intermixing. In contrast, the field-like torque, which is small in the case of an ideal interface, is dramatically enhanced by intermixing. |
Tuesday, March 16, 2021 9:00AM - 9:12AM Live |
E38.00004: Voltage Controlled Spin-Orbit Torque Switching in W/CoFeB/MgO Jinsong Xu, Chia-Ling Chien Voltage control of magnetism and spintronics have been highly desirable, but rarely realized. In this work, we show voltage-controlled spin-orbit torque (SOT) switching in W/CoFeB/MgO films with perpendicular magnetic anisotropy (PMA) as administered through SrTiO3 with a high dielectric constant. We show that a DC voltage can significantly lower PMA by 45%, reduce switching current by 23%, and increase the damping-like torque as revealed by the first and second-harmonic measurements. These are characteristics that are prerequisites for voltage-controlled and voltage-select SOT switching spintronic devices. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E38.00005: Strong, anisotropic in-plane and out-of-plane damping-like spin-orbit torque in epitaxial RuO2 Arnab Bose, Nathaniel Schreiber, Hari Nair, Xiyue S Zhang, Rakshit Jain, Thow Min Jerald Cham, Jiaxin Sun, David Anthony Muller, Robert Alan Buhrman, Darrell Schlom, Daniel C Ralph We study spin torques in RuO2/Permalloy bilayers grown on TiO2 substrates by second-harmonic Hall and spin-torque ferromagnetic resonance techniques [1]. Epitaxial RuO2 films exhibit a strong out-of-plane damping-like torque (OOP-DLT) that is anisotropic as a function of the orientation of current flow relative to the RuO2 crystal axes. This OOP-DLT is absent in similarly prepared IrO2/Permalloy samples despite the fact that RuO2 and IrO2 possess similar crystal structures [2]. This suggests that the recently-discovered antiferromagnetism in RuO2 [3] provides the symmetry breaking that allows the OOP-DLT [4]. We also observe a sizable in-plane damping-like torque originating from RuO2. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E38.00006: Prediction of Purely Interfacial Giant Antidamping Spin-Orbit Torque induced by Skew Scattering Alessandro Veneri, Aires Ferreira
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Tuesday, March 16, 2021 9:36AM - 10:12AM Live |
E38.00007: Spin-Orbit Torque Switching of Ferromagnets and Antiferromagnets Invited Speaker: Chia-Ling Chien Spin-orbit torque (SOT), using pure spin current from heavy metals (HMs) to switch ferromagnets (FMs), enables electrical switching in FM/HM bilayers, where the FM magnetization before and after SOT can be unequivocally verified. We discuss schemes that can achieve field-free SOT switching of FM with perpendicular magnetic anisotropy (PMA). Far more challenging is SOT switching of antiferromagnetic (AF) Néel vector, whose existence cannot be readily verified. SOT switching of AF has been claimed in patterned 8- or 4-terminal AF/HM bilayers by applying a high current density. However, similar voltages remain without the AF layer, demonstrating that the signals are unrelated to AF switching but the thermal signals from the HM. SOT switching in synthetic AF consisting of two interlayer-coupled FMs with PMA reveals SOT switching efficiency in a magnetic entity with different net magnetizations and directions. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E38.00008: Electric field induced exceptional points and mode attraction in a spin-orbit torque oscillator Igor Proskurin, Robert Stamps In spin-orbit torque oscillators, spin magnetic moment is transferred from conducting electrons inside a material with spin-orbit coupling to a magnetic oscillator, which modifies its dynamic and dissipative properties. We consider resonant spin-orbit torque system in applied electric field and demonstrate that this system can realize exceptional points in the energy spectrum of the magnetic oscillator. This requires balance of the dissipations in the electron and magnetic systems and special symmetry requirements. We show that if the oscillator realizes two exceptional points, it enters so-called mode attraction regime, which in some way is reminiscent of the mode synchronization. In this regime, the real part of the oscillator frequency is locked with the frequency of the interband electron transitions inside the material with spin-orbit coupling. We estimate electric field needed to reach the attraction regime for a spin-orbit torque oscillator with Rashba coupling and make proposals for experimental detection using the magnetic susceptibility measurements. We also demonstrate that the exceptional points in this system can be electrically controlled that may have utility in electric-field switching of the oscillator modes. |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E38.00009: Magneto-Optical Detection of Spin-Orbit Torque Phenomena Using Sagnac Interferometer microscope Zhengjie Huang, Eric Vetter, Yuzan Xiong, Wei Zhang, Dali Sun Spin-orbit torques (SOTs), direct control of the magnetization via spin-orbit interaction, have been demonstrated in a variety of ferromagnetic/non-magnetic heavy metal bilayers utilizing both magneto-transport and magneto-optical Kerr effect (MOKE) measurements. Whereas the conventional MOKE measurement successfully enables the detectability of SOTs, an AC current modulation in the SOT devices is required to achieve the desired sensitivity. Here, we show that without the AC current modulation, the SOT-induced effect can be studied by observing static magnetization switching under a DC current excitation taking advantage of the ultrahigh sensitivity of a Sagnac interferometer microscope. Upon the DC current excitation, spatially resolved static magnetization switching in a prototypical SOT device, i.e., NiFe/Pt bilayer is directly measured, by which a current-induced Oersted field, joule-heating, and other parasite artifacts can be well-separated. Our work provides a promising continuous-wave magneto-optical approach to optically characterize the static spin Hall angle in a range of SOT devices without the AC current modulation.<gdiv></gdiv> |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E38.00010: Thermal stability and memristive spin-orbit torque switching at elevated temperature Wei-Bang Liao, Tian-Yue Chen, Yu-Chan Hsiao, Chi-Feng Pai Recently, many spin-orbit torque (SOT) related works commit to enhancing the SOT efficiency but neglect the thermal stabilities. The thermal stability factor (Δ) is crucial for robust storage, especially when SOT-based devices integrated with CMOS. The thermal dissipation from transistor can cause the increase of ambient temperature and therefore may affect the performance of SOT efficiency and thermal stability. Additionally, the thermal effect may have influence on the multi-states in memristive switching which can be controlled by changing the applied currents widths. |
Tuesday, March 16, 2021 10:48AM - 11:00AM Live |
E38.00011: Spin transparency of Pt-based heavy metal/ferromagnet interface Lijun Zhu, Daniel C Ralph, Robert Alan Buhrman Strong spin-orbit torques (SOTs) in heavy metal/ferromagnet (HM/FM) systems can efficiently manipulate magnetization at the nanoscale. When the spin Hall effect of the HMs is the dominant source of the SOTs as is the case for many HM/FM systems, achieving high spin transparency (Tint) of the interface is of the same importance as achieving a large spin Hall ratio in the HMs [1-3] for obtaining a large damping-like SOT. In Pt-based HM/FM system where electrons mediate the spin transport, spin backflow [4,5] inevitably reduces Tint by more than 50% [6] while the“spin memory loss”can further reduce Tint if the interfacial spin-orbit coupling is strong [7-10]. In this talk, we will discuss the strategies developed to effectively minimize or even eliminate spin backflow and spin memory loss. |
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