Bio


Xiang (Shaun) Li is a postdoctoral scholar at Stanford University, advised by Prof. Shan X. Wang. He received his Ph.D. degree in Electrical and Computer Engineering from UCLA in 2018, under the mentorship of Prof. Kang L. Wang. He received his B.S. in Physics degree at Peking University in 2013. His research interests lie in novel magnetic materials and devices for memory-intensive applications and neuromorphic architectures. He is also interested in technology commercialization. From 2016 to 2017, he was a Technology Fellow at UCLA Technology Development Group analyzing technical merit and market potential for UCLA intellectual property. From 2017 to 2018, he was responsible for technical partnership and investor development at Inston Inc., a startup spin-off from UCLA.

Honors & Awards


  • 2016 IEEE Magnetics Society Summer School, IEEE Magnetics Society (2016/08)
  • Best Poster Award, 2015 Non-Volatile Memory Technology Symposium (2015/10)
  • Outstanding Graduate, City of Beijing, China (2013/07)
  • Outstanding Graduate, Peking University, Beijing, China (2013/07)
  • AEON Scholarship, Peking University, Beijing, China (2012/09)
  • Robin Li Scholarship, Peking University, Beijing, China (2011/09)
  • Yang Fuqing & Wang Yangyuan Academician Scholarship, Peking University, Beijing, China (2010/09)

Boards, Advisory Committees, Professional Organizations


  • Referee, Science Advances (2018 - Present)
  • Referee, Applied Physics Letters (2018 - Present)
  • Referee, IEEE Transactions on Electron Devices (2018 - Present)
  • Referee, IEEE Transaction on Magnetics - Conferences (2018 - Present)
  • Referee, IEEE Journal of the Electron Devices Society (2018 - Present)

Professional Education


  • B.S., Peking University, China, Physics (2013)
  • M.S., University of California, Los Angeles (UCLA), Electrical Engineering (2016)
  • Ph.D., University of California, Los Angeles (UCLA), Electrical and Computer Engineering (2018)

Current Research and Scholarly Interests


Enabled by machine learning, low-power electronic sensors and devices promise to understand, interact with and aid all human activities. Faster, more energy-efficient and denser information storage and compute will be the foundation of this future. Leveraging the unique physics of topological materials, we aim to build this foundation based on spin-orbit torque magnetic tunnel junctions. We will also work closely with industry to enable system-level performance transformations.

Projects


  • Topological Materials and Interfaces for Advanced SOT-MRAM

    Location

    McCullough building

All Publications


  • Voltage-controlled magnetoelectric memory and logic devices MRS BULLETIN Li, X., Lee, A., Razavi, S., Wu, H., Wang, K. L. 2018; 43 (12): 970–77
  • Enhancement of voltage-controlled magnetic anisotropy through precise control of Mg insertion thickness at CoFeB vertical bar MgO interface APPLIED PHYSICS LETTERS Li, X., Fitzell, K., Wu, D., Karaba, C., Buditama, A., Yu, G., Wong, K. L., Altieri, N., Grezes, C., Kioussis, N., Tolbert, S., Zhang, Z., Chang, J. P., Amiri, P., Wang, K. L. 2017; 110 (5)

    View details for DOI 10.1063/1.4975160

    View details for Web of Science ID 000394057600019

  • Write Error Rate and Read Disturbance in Electric-Field-Controlled Magnetic Random-Access Memory IEEE MAGNETICS LETTERS Grezes, C., Lee, H., Lee, A., Wang, S., Ebrahimi, F., Li, X., Wong, K., Katine, J. A., Ocker, B., Langer, J., Gupta, P., Amiri, P., Wang, K. L. 2017; 8
  • Enhanced voltage-controlled magnetic anisotropy in magnetic tunnel junctions with an MgO/PZT/MgO tunnel barrier APPLIED PHYSICS LETTERS Chien, D., Li, X., Wong, K., Zurbuchen, M. A., Robbennolt, S., Yu, G., Tolbert, S., Kioussis, N., Amiri, P., Wang, K. L., Chang, J. P. 2016; 108 (11)

    View details for DOI 10.1063/1.4943023

    View details for Web of Science ID 000373058400025

  • Room-Temperature Creation and Spin Orbit Torque Manipulation of Skyrmions in Thin Films with Engineered Asymmetry NANO LETTERS Yu, G., Upadhyaya, P., Li, X., Li, W., Kim, S., Fan, Y., Wong, K. L., Tserkovnyak, Y., Amiri, P., Wang, K. L. 2016; 16 (3): 1981–88

    Abstract

    Magnetic skyrmions, which are topologically protected spin textures, are promising candidates for ultralow-energy and ultrahigh-density magnetic data storage and computing applications. To date, most experiments on skyrmions have been carried out at low temperatures. The choice of available materials is limited, and there is a lack of electrical means to control skyrmions in devices. In this work, we demonstrate a new method for creating a stable skyrmion bubble phase in the CoFeB-MgO material system at room temperature, by engineering the interfacial perpendicular magnetic anisotropy of the ferromagnetic layer. Importantly, we also demonstrate that artificially engineered symmetry breaking gives rise to a force acting on the skyrmions, in addition to the current-induced spin-orbit torque, which can be used to drive their motion. This room-temperature creation and manipulation of skyrmions offers new possibilities to engineer skyrmionic devices. The results bring skyrmionic memory and logic concepts closer to realization in industrially relevant and manufacturable thin film material systems.

    View details for DOI 10.1021/acs.nanolett.5b05257

    View details for Web of Science ID 000371946300068

    View details for PubMedID 26848783

  • Thermally stable voltage-controlled perpendicular magnetic anisotropy in Mo vertical bar CoFeB vertical bar MgO structures APPLIED PHYSICS LETTERS Li, X., Yu, G., Wu, H., Ong, P. V., Wong, K., Hu, Q., Ebrahimi, F., Upadhyaya, P., Akyol, M., Kioussis, N., Han, X., Amiri, P., Wang, K. L. 2015; 107 (14)

    View details for DOI 10.1063/1.4932553

    View details for Web of Science ID 000363422100040

  • Interface control of domain wall depinning field Huang, Y., Li, X., Wang, L., Yu, G., Wang, K. L., Zhao, W. AMER INST PHYSICS. 2018

    View details for DOI 10.1063/1.5007270

    View details for Web of Science ID 000433954000298

  • Voltage-Controlled Magnetic Tunnel Junctions for Processing-In-Memory Implementation IEEE ELECTRON DEVICE LETTERS Wang, L., Kang, W., Ebrahimi, F., Li, X., Huang, Y., Zhao, C., Wang, K. L., Zhao, W. 2018; 39 (3): 440–43
  • Interfacial Dzyaloshinskii-Moriya Interaction: Effect of 5d Band Filling and Correlation with Spin Mixing Conductance. Physical review letters Ma, X., Yu, G., Tang, C., Li, X., He, C., Shi, J., Wang, K. L., Li, X. 2018; 120 (15): 157204

    Abstract

    The Dzyaloshinskii-Moriya interaction (DMI) at the heavy metal (HM) and ferromagnetic metal (FM) interface has been recognized as a key ingredient in spintronic applications. Here we investigate the chemical trend of DMI on the 5d band filling (5d^{3}-5d^{10}) of the HM element in HM/FM (FM=CoFeB,Co)/MgO multilayer thin films. DMI is quantitatively evaluated by measuring asymmetric spin wave dispersion using Brillouin light scattering. Sign reversal and 20 times modification of the DMI coefficient D have been measured as the 5d HM element is varied. The chemical trend can be qualitatively understood by considering the 5d and 3d bands alignment at the HM/FM interface and the subsequent orbital hybridization around the Fermi level. Furthermore, a correlation is observed between DMI and effective spin mixing conductance at the HM/FM interfaces. Our results provide new insights into the interfacial DMI for designing future spintronic devices.

    View details for PubMedID 29756869

  • Large voltage-controlled magnetic anisotropy in the SrTiO3/Fe/Cu structure APPLIED PHYSICS LETTERS Peng, S., Li, S., Kang, W., Zhou, J., Lei, N., Zhang, Y., Yang, H., Li, X., Amiri, P., Wang, K. L., Zhao, W. 2017; 111 (15)

    View details for DOI 10.1063/1.4996275

    View details for Web of Science ID 000413196100020

  • Partial spin absorption induced magnetization switching and its voltage-assisted improvement in an asymmetrical all spin logic device at the mesoscopic scale APPLIED PHYSICS LETTERS Zhang, Y., Zhang, Z., Wang, L., Nan, J., Zheng, Z., Li, X., Wong, K., Wang, Y., Klein, J., Amiri, P., Zhang, Y., Wang, K. L., Zhao, W. 2017; 111 (5)

    View details for DOI 10.1063/1.4997422

    View details for Web of Science ID 000418467700013

  • Dzyaloshinskii-Moriya Interaction across an Antiferromagnet-Ferromagnet Interface PHYSICAL REVIEW LETTERS Ma, X., Yu, G., Razavi, S. A., Sasaki, S. S., Li, X., Hao, K., Tolbert, S. H., Wang, K. L., Li, X. 2017; 119 (2): 027202

    Abstract

    The antiferromagnet- (AFM-)ferromagnet (FM) interfaces are of central importance in recently developed pure electric or ultrafast control of FM spins, where the underlying mechanisms remain unresolved. Here we report the direct observation of an Dzyaloshinskii-Moriya interaction (DMI) across the AFM-FM interface of IrMn/CoFeB thin films. The interfacial DMI is quantitatively measured from the asymmetric spin-wave dispersion in the FM layer using Brillouin light scattering. The DMI strength is enhanced by a factor of 7 with increasing IrMn layer thickness in the range of 1-7.5 nm. Our findings provide deeper insight into the coupling at the AFM-FM interface and may stimulate new device concepts utilizing chiral spin textures such as magnetic Skyrmions in AFM-FM heterostructures.

    View details for PubMedID 28753324

  • Perpendicular magnetic tunnel junction with W seed and capping layers JOURNAL OF APPLIED PHYSICS Almasi, H., Sun, C. L., Li, X., Newhouse-Illige, T., Bi, C., Price, K. C., Nahar, S., Grezes, C., Hu, Q., Amiri, P., Wang, K. L., Voyles, P. M., Wang, W. G. 2017; 121 (15)

    View details for DOI 10.1063/1.4981878

    View details for Web of Science ID 000399903200010

  • Room-Temperature Skyrmion Shift Device for Memory Application NANO LETTERS Yu, G., Upadhyaya, P., Shao, Q., Wu, H., Yin, G., Li, X., He, C., Jiang, W., Han, X., Amiri, P., Wang, K. L. 2017; 17 (1): 261–68

    Abstract

    Magnetic skyrmions are intensively explored for potential applications in ultralow-energy data storage and computing. To create practical skyrmionic memory devices, it is necessary to electrically create and manipulate these topologically protected information carriers in thin films, thus realizing both writing and addressing functions. Although room-temperature skyrmions have been previously observed, fully electrically controllable skyrmionic memory devices, integrating both of these functions, have not been developed to date. Here, we demonstrate a room-temperature skyrmion shift memory device, where individual skyrmions are controllably generated and shifted using current-induced spin-orbit torques. Particularly, it is shown that one can select the device operation mode in between (i) writing new single skyrmions or (ii) shifting existing skyrmions by controlling the magnitude and duration of current pulses. Thus, we electrically realize both writing and addressing of a stream of skyrmions in the device. This prototype demonstration brings skyrmions closer to real-world computing applications.

    View details for DOI 10.1021/acs.nanolett.6b04010

    View details for Web of Science ID 000392036600038

    View details for PubMedID 27966987

  • Spin-orbit torques in perpendicularly magnetized Ir22Mn78/Co20Fe60B20/MgO multilayer APPLIED PHYSICS LETTERS Wu, D., Yu, G., Chen, C., Razavi, S., Shao, Q., Li, X., Zhao, B., Wong, K. L., He, C., Zhang, Z., Amiri, P., Wang, K. L. 2016; 109 (22)

    View details for DOI 10.1063/1.4968785

    View details for Web of Science ID 000390243100027

  • Interfacial control of Dzyaloshinskii-Moriya interaction in heavy metal/ferromagnetic metal thin film heterostructures PHYSICAL REVIEW B Ma, X., Yu, G., Li, X., Wang, T., Wu, D., Olsson, K. S., Chu, Z., An, K., Xiao, J. Q., Wang, K. L., Li, X. 2016; 94 (18)
  • Spin-torque ferromagnetic resonance measurements utilizing spin Hall magnetoresistance in W/Co40Fe40B20/MgO structures APPLIED PHYSICS LETTERS He, C., Navabi, A., Shao, Q., Yu, G., Wu, D., Zhu, W., Zheng, C., Li, X., He, Q., Razavi, S., Wong, K. L., Zhang, Z., Amiri, P., Wang, K. L. 2016; 109 (20)

    View details for DOI 10.1063/1.4967843

    View details for Web of Science ID 000388000000030

  • In-plane current-driven spin-orbit torque switching in perpendicularly magnetized films with enhanced thermal tolerance APPLIED PHYSICS LETTERS Wu, D., Yu, G., Shao, Q., Li, X., Wu, H., Wong, K. L., Zhang, Z., Han, X., Amiri, P., Wang, K. L. 2016; 108 (21)

    View details for DOI 10.1063/1.4952771

    View details for Web of Science ID 000377024400032

  • Competing effect of spin-orbit torque terms on perpendicular magnetization switching in structures with multiple inversion asymmetries SCIENTIFIC REPORTS Yu, G., Akyol, M., Upadhyaya, P., Li, X., He, C., Fan, Y., Montazeri, M., Alzate, J. G., Lang, M., Wong, K. L., Amiri, P., Wang, K. L. 2016; 6: 23956

    Abstract

    Current-induced spin-orbit torques (SOTs) in structurally asymmetric multilayers have been used to efficiently manipulate magnetization. In a structure with vertical symmetry breaking, a damping-like SOT can deterministically switch a perpendicular magnet, provided an in-plane magnetic field is applied. Recently, it has been further demonstrated that the in-plane magnetic field can be eliminated by introducing a new type of perpendicular field-like SOT via incorporating a lateral structural asymmetry into the device. Typically, however, when a current is applied to such devices with combined vertical and lateral asymmetries, both the perpendicular field-like torque and the damping-like torque coexist, hence jointly affecting the magnetization switching behavior. Here, we study perpendicular magnetization switching driven by the combination of the perpendicular field-like and the damping-like SOTs, which exhibits deterministic switching mediated through domain wall propagation. It is demonstrated that the role of the damping-like SOT in the deterministic switching is highly dependent on the magnetization direction in the domain wall. By contrast, the perpendicular field-like SOT is solely determined by the relative orientation between the lateral structural asymmetry and the current direction, regardless of the magnetization direction in the domain wall. The experimental results further the understanding of SOTs-induced switching, with implications for spintronic devices.

    View details for DOI 10.1038/srep23956

    View details for Web of Science ID 000373431800001

    View details for PubMedID 27050160

    View details for PubMedCentralID PMC4822117

  • Influence of inserted Mo layer on the thermal stability of perpendicularly magnetized Ta/Mo/Co20Fe60B20/MgO/Ta films AIP ADVANCES Li, M., Lu, J., Yu, G., Li, X., Han, G., Chen, X., Shi, H., Yu, G., Amiri, P., Wang, K. L. 2016; 6 (4)

    View details for DOI 10.1063/1.4947075

    View details for Web of Science ID 000375845100032

  • Magneto-optical investigation of spin-orbit torques in metallic and insulating magnetic heterostructures NATURE COMMUNICATIONS Montazeri, M., Upadhyaya, P., Onbasli, M. C., Yu, G., Wong, K. L., Lang, M., Fan, Y., Li, X., Amiri, P., Schwartz, R. N., Ross, C. A., Wang, K. L. 2015; 6: 8958

    Abstract

    Manipulating magnetism by electric current is of great interest for both fundamental and technological reasons. Much effort has been dedicated to spin-orbit torques (SOTs) in metallic structures, while quantitative investigation of analogous phenomena in magnetic insulators remains challenging due to their low electrical conductivity. Here we address this challenge by exploiting the interaction of light with magnetic order, to directly measure SOTs in both metallic and insulating structures. The equivalency of optical and transport measurements is established by investigating a heavy-metal/ferromagnetic-metal device (Ta/CoFeB/MgO). Subsequently, SOTs are measured optically in the contrasting case of a magnetic-insulator/heavy-metal (YIG/Pt) heterostructure, where analogous transport measurements are not viable. We observe a large anti-damping torque in the YIG/Pt system, revealing its promise for spintronic device applications. Moreover, our results demonstrate that SOT physics is directly accessible by optical means in a range of materials, where transport measurements may not be possible.

    View details for DOI 10.1038/ncomms9958

    View details for Web of Science ID 000367578000002

    View details for PubMedID 26643048

    View details for PubMedCentralID PMC4686864

  • Strain-induced modulation of perpendicular magnetic anisotropy in Ta/CoFeB/MgO structures investigated by ferromagnetic resonance (vol 106, 072402, 2015) APPLIED PHYSICS LETTERS Yu, G., Wang, Z., Abolfath-Beygi, M., He, C., Li, X., Wong, K. L., Nordeen, P., Wu, H., Ong, P. V., Kioussis, N., Carman, G. P., Han, X., Alhomoudi, I. A., Amiri, P., Wang, K. L. 2015; 106 (16)

    View details for DOI 10.1063/1.4918984

    View details for Web of Science ID 000353559900049

  • Current-induced spin-orbit torque switching of perpendicularly magnetized Hf vertical bar CoFeB vertical bar MgO and Hf vertical bar CoFeB vertical bar TaOx structures APPLIED PHYSICS LETTERS Akyol, M., Yu, G., Alzate, J. G., Upadhyaya, P., Li, X., Wong, K. L., Ekicibil, A., Amiri, P., Wang, K. L. 2015; 106 (16)

    View details for DOI 10.1063/1.4919108

    View details for Web of Science ID 000353559900027

  • Current-driven perpendicular magnetization switching in Ta/CoFeB/[TaOx or MgO/TaOx] films with lateral structural asymmetry APPLIED PHYSICS LETTERS Yu, G., Chang, L., Akyol, M., Upadhyaya, P., He, C., Li, X., Wong, K. L., Amiri, P., Wang, K. L. 2014; 105 (10)

    View details for DOI 10.1063/1.4895735

    View details for Web of Science ID 000342758700044