Magnetic Nanostructures: A Playground for Fundamental Physics

Ran Cheng
Thursday, March 2, 2017 - 4:30pm to 5:30pm

Nature becomes amazingly different from what we perceive with our eyes when zoomed in to the nanometer scale, where atomic spins interact and form diverse magnetic configurations. Besides holding great technological promise, magnetic nanostructures have also enabled a vibrant playground for fundamental physics—a thriving field known as spintronics. In this talk, I will introduce selected recent progress in spintronics that has reshaped our understanding of transport phenomena occurring at the microscopic scale. Special attention will be paid to antiferromagnetic...

Nitin Samarth (Penn State): Topological Spintronics: From the Haldane Phase to Spin Devices

We provide a perspective on the recent emergence of “topological spintronics,” which relies on the existence of helical Dirac electrons in condensed matter. Spin- and angle-resolved photoemission spectroscopy shows how the spin texture of these electronic states can be engineered using quantum tunneling [1] or by breaking time-reversal symmetry [2]. Inappropriately designed systems, broken time-reversal symmetry transforms helical Dirac states into chiral edge states, a realization of Haldane’s Chern insulator phase of matter. This is characterized by a precisely quantized Hall conductance and dissipationless edge transport without a magnetic field. We show how these edge states can be quantitatively characterized by analyzing their giant anisotropic magnetoresistance [3]. At miilikelvin temperatures, the interplay between Chern states and disordered magnetism [4] results in surprising behavior, perhaps consistent with quantum tunneling out of a ‘false vacuum’ [5]. Finally, we show how these helical Dirac electrons provide a possible pathway toward a spin device technology that works at room temperature [6,7].

[1] M. Neupane, A. Richardella et al.,Nature Communications 5, 3841 (2014).
[2] S.-Y. Xu et al., Nature Physics 8, 616 (2012).
[3] A. Kandala,A. Richardella, et al.,Nature Communications 6, 7434 (2015).
[4] E. Lachman et al., Science Advances 1, e1500740(2015).
[5] Minhao Liu et al., Science Advances 2, e1600167(2016).

Topological Spintronics: From the Haldane Phase to Spin Devices

Nitin Samarth
Monday, November 28, 2016 - 4:30pm to 6:00pm

We provide a perspective on the recent emergence of “topological spintronics,” which relies on the existence of helical Dirac electrons in condensed matter. Spin- and angle-resolved photoemission spectroscopy shows how the spin texture of these electronic states can be engineered using quantum tunneling [1] or by breaking time-reversal symmetry [2]. Inappropriately designed systems, broken time-reversal symmetry transforms helical Dirac states into chiral edge states, a realization of Haldane’s Chern insulator phase of matter. This is characterized by a precisely...

Next-Generation Computing using Spin-Based Materials

Jean Anne C. Incorvia
Friday, October 28, 2016 - 12:00pm to 1:30pm

We are at a time where the electronics industry is feeling pressure from two sides on the small scale we are facing the fundamental physical limits of silicon, and on the large scare we are facing new, abundant-data and distributed-data applications, such as for the internet of things. The future of computing will require both more energy efficient electronics and more big-data driven, application-specific designs.

Magnetic devices are a promising candidate for future electronics, due to their low-voltage operation...

Energetic Molding of Chiral Magnetic Bubbles

  • By Aude Marjolin
  • 21 July 2016

When it comes to computers, people never look for “bigger and better,” but rather “smaller and faster.” How do we continue to keep up with that demand, making technology smaller, faster, and more energy-efficient? According to Vincent Sokalski, the answer may be in the fundamental origins of magnets—the spin of electrons.

Sokalski and his group studied the interaction of electron spins in magnetic materials poised for use in next-generation cellphones and computers and discovered how to better measure and predict the changing magnetic state of those materials. This new understanding, recently published in Physical Review B under the title "Energetic Molding of Chiral Magnetic Bubbles", is exciting for the future of computing technology because it will allow scientists to explore and develop materials that are more energy-efficient and faster than traditional semiconductor-based materials.

Sara Majetich May Be Building the Computers of the Future

  • By Aude Marjolin
  • 24 February 2016

“The computers of the future may be born in Sara Majetich’s labs” reads the header of a recent news article.

For the past three years, Majetich has been a principal investigator for the Center for Spintronic Materials, Interfaces, and Novel Architectures (C-SPIN), which coordinates the research of 32 professors from 18 universities towards overcoming the limits of traditional computer design with spintronic technology.

Department of Electrical and Computer Engineering, Carnegie Mellon University
Ph.D., Physics, University of California, San Diego, 1989

Dr. Zhu’s research has been in the field of magnetic data storage technologies. His research work on the microstructure of thin film recording media has been pivotal for hard disk drives to reach today’s storage capacity. He has pioneered the research on utilizing micromagnetic modeling for MRAM memory design and established some of the most fundamental design principles used today.

Magnetic Recording Technology for Hard Disk Drives and Digital Tape Recording: Magnetic recording technology has been advancing in dramatically rapid pace over the past decade during which we have made some important contributions. At present, our research includes:

  • Development of novel recording mechanisms that enables area storage density exceeding 1 Tbits/in^2 for hard disk drive applications;
  • Development of novel perpendicular thin film media microstructures that capable of high area density applications;
    The research is supported by DSSC and its industrial sponsors.

Innovative Designs of Magnetic Random Access Memory (MRAM): MRAM has the potential to replace SRAM, DRAM, FLASH, and even a small disk drive to be the universal memory for computer data storage, enabling an entire computer system to be made on a single chip. Our research focuses on novel MRAM designs that offer robust and repeatable magnetic switching characteristic, low operation power capability, and sufficient thermal-magnetic stability. Micromagnetic modeling on computers is utilized to aid the design process and the devices are fabricated using the state-of-the-art e-beam and optical lithographic fabrication technology. Our collaborators include the Naval Research Laboratory and Nonvolatile Electronics Corporation. This research is current funded by the Office of Naval Research, Pittsburgh Digital Green House, STMicroelectronics, and DSSC.

Understanding Noise in Nano-Magnetic Systems: Thermally excited magnetization precession and spin current induced chaotic spin waves are two important causes of magnetic noise in advanced nano-scale magnetic sensors. We perform both theoretical analysis and experimental measurements to obtain a good understanding of the noise and the corresponding underlying physics. This research is supported by Seagate Technology and DSSC.

Most Cited Publications
  1. "Ultrahigh density vertical magnetoresistive random access memory." Jian-Gang Zhu, Youfeng Zheng, Gary A Prinz. Journal of Applied Physics.
  2. "Microwave assisted magnetic recording." Jian-Gang Zhu, Xiaochun Zhu, Yuhui Tang. IEEE Transactions on Magnetics.
  3. "Micromagnetic studies of thin metallic films." Jian‐Gang Zhu, H Neal Bertram. Journal of applied physics.
  4. "Signature microRNA expression profile of essential hypertension and its novel link to human cytomegalovirus infection." Shuqiang Li, Jianguo Zhu, Weili Zhang, Youren Chen, Ke Zhang, Laurentiu M Popescu, Xinliang Ma, Wayne Bond Lau, Rong Rong, Xueqing Yu, Bingbing Wang, Yafeng Li, Chuanshi Xiao, Mingming Zhang, Shuyan Wang, Liping Yu, Alex F Chen, Xinchun Yang, Jun Cai. Circulation.
  5. "Magnetoresistive random access memory: The path to competitiveness and scalability." Jian-Gang Zhu. Proceedings of the IEEE.
Recent Publications
  1. "3d perpendicular magnetic crossbar memory." Jian-Gang Zhu, Chia-Ling Chien, Qinli Ma. US.
  2. "Dynamic Modeling and Feedforward Control of Jaw Movements Driven by Viscoelastic Artificial Muscles." Ujjaval Gupta, Yuzhe Wang, Hongliang Ren, Jian Zhu. IEEE/ASME Transactions on Mechatronics.
  3. "Construction of electrochemical storage cell." Weixin Zheng, Luxia Jiang, Jianhua Zhu, Xi Shen. US.
  4. "Orthogonal decomposition of core loss along rolling and transverse directions of non-grain oriented silicon steels." Xuezhi Wan, Yongjian Li, Jingsong Li, Chengcheng Liu, Jianguo Zhu. AIP Advances.
  5. "Technique that enhances the manipulation of an HTML tree presentation by using an array representation of the hierarchical path of a tree node." Trevett B Chusing, Lei Zhang, Jian Zhu. US.
Department of Materials Science and Engineering, Carnegie Mellon University
Ph.D., Materials Science and Engineering, Carnegie Mellon University, 2011

Our research is focused on the exploration of novel magnetic & spintronic materials for memory, logic, and HDD storage applications. We concentrate on the development of thin films & nanoscale devices that will enable improved energy efficiency, non-volatility, and scalability to ever-decreasing dimensions. Current research efforts include crystallographic & microstructural characterization of perpendicular magnetic recording media, materials for spin hall effect devices, spin transfer torque magneto-resistive random access memory (STT-MRAM), and magnetic interactions in soft nanogranular composite thin films.

Most Cited Publications
  1. "Optimization of Ta thickness for perpendicular magnetic tunnel junction applications in the MgO-FeCoB-Ta system." Vincent Sokalski, Matthew T Moneck, En Yang, Jian-Gang Zhu. Applied Physics Letters.
  2. "Energetic molding of chiral magnetic bubbles." Derek Lau, Vignesh Sundar, Jian-Gang Zhu, Vincent Sokalski. Physical review B.
  3. "Experimental modeling of intergranular exchange coupling for perpendicular thin film media." Vincent Sokalski, David E Laughlin, Jian-Gang Zhu. Applied physics letters.
  4. "Dispersive stiffness of Dzyaloshinskii domain walls." JP Pellegren, Derek Lau, Vincent Sokalski. Physical review letters.
  5. "Experimental demonstration of four-terminal magnetic logic device with separate read-and write-paths." DM Bromberg, MT Moneck, VM Sokalski, J Zhu, L Pileggi, J-G Zhu. 2014 IEEE International Electron Devices Meeting.
Recent Publications
  1. "Formation of zero-field Skyrmion arrays in asymmetric superlattices." Maxwell Li, Anish Rai, Ashok Pokhrel, Arjun Sapkota, Claudia Mewes, Tim Mewes, Marc De Graef, Vincent Sokalski. arXiv preprint arXiv:1911.03578.
  2. "Stabilization of coupled Dzyaloshinskii domain walls in fully compensated synthetic anti-ferromagnets." Nisrit Pandey, Maxwell Li, Marc De Graef, Vincent Sokalski. arXiv preprint arXiv:1910.11421.
  3. "Lorentz TEM Imaging of Topological Magnetic Features in Asymmetric [Pt/(Co/Ni)M/Ir]N based Multi-Layers." Maxwell Li, Derek Lau, Marc De Graef, Vincent Sokalski. Microscopy and Microanalysis.
  4. "Lorentz TEM investigation of chiral spin textures and Néel Skyrmions in asymmetric multi-layer thin films." Maxwell Li, Derek Lau, Marc De Graef, Vincent Sokalski. Physical Review Materials.
  5. "Magnetic domain wall skyrmions." Ran Cheng, Maxwell Li, Arjun Sapkota, Anish Rai, Ashok Pokhrel, Tim Mewes, Claudia Mewes, Di Xiao, Marc De Graef, Vincent Sokalski. Physical Review B.
Department of Physics, Carnegie Mellon University
Ph.D., University of Georgia

My research focuses on magnetic nanoparticles that have very uniform sizes, and we study their fundamental behavior, as well as possible applications in data storage media, permanent magnets, and biomedicine. One of the consequences of this monodispersity is that the particles can then self-assemble into arrays (shown below), just as atoms come together to form a crystal. We are investigating the collective behavior of the nanoparticle arrays that are analogous to those in crystals. Isolated iron atoms do not interact with each other and are paramagnetic, but in an iron crystal the interactions lead to ferromagnetism. Superparamagnetic-to-ferromagnetic and insulator-to-metal phase transitions are expected as the nanoparticles are brought closer together. We have also developed a method to replace the surfactant coating the particles with an inorganic matrix, and are exploring methods that exploit this approach to prepare functional nanocomposites.

Most Cited Publications
  1. "TCE dechlorination rates, pathways, and efficiency of nanoscale iron particles with different properties." Yueqiang Liu, Sara A Majetich, Robert D Tilton, David S Sholl, Gregory V Lowry. Environmental science & technology.
  2. "Synthesis and utilization of monodisperse superparamagnetic colloidal particles for magnetically controllable photonic crystals." Xiangling Xu, Gary Friedman, Keith D Humfeld, Sara A Majetich, Sanford A Asher. Chemistry of Materials.
  3. "Superparamagnetism in carbon-coated Co particles produced by the Kratschmer carbon arc process." ME McHenry, SA Majetich, JO Artman, M DeGraef, SW Staley. Physical Review B.
  4. "The 2014 magnetism roadmap." Robert L Stamps, Stephan Breitkreutz, Johan Åkerman, Andrii V Chumak, YoshiChika Otani, Gerrit EW Bauer, Jan-Ulrich Thiele, Martin Bowen, Sara A Majetich, Mathias Kläui, Ioan Lucian Prejbeanu, Bernard Dieny, Nora M Dempsey, Burkard Hillebrands. Journal of Physics D: Applied Physics.
  5. "Preparation and characterization of monodisperse Fe nanoparticles." Dorothy Farrell, Sara A Majetich, Jess P Wilcoxon. The Journal of Physical Chemistry B.
Recent Publications
  1. "Magnetic stray fields in nanoscale magnetic tunnel junctions." Sarah Jenkins, Andrea Meo, Luke E Elliott, Stephan K Piotrowski, Mukund Bapna, Roy W Chantrell, Sara A Majetich, Richard FL Evans. Journal of Physics D: Applied Physics.
  2. "Electric field switchable magnetic devices." Jian-Ping Wang, Delin Zhang, Sara A Majetich, Mukund Bapna. US.
  3. "The role of faceting and elongation on the magnetic anisotropy of magnetite Fe3O4 nanocrystals." Roberto Moreno, Samuel Poyser, Daniel Meilak, Andrea Meo, Sarah Jenkins, Vlado K Lazarov, Gonzalo Vallejo-Fernandez, Sara Majetich, Richard FL Evans. arXiv preprint arXiv:1909.02470.
  4. "Effect of Mo capping in sub-100 nm CoFeB-MgO tunnel junctions with perpendicular magnetic anisotropy." Mukund Bapna, Brad Parks, Samuel Oberdick, Hamid Almasi, Congli Sun, Paul Voyles, Weigang Wang, Sara A Majetich. Journal of Magnetism and Magnetic Materials.
  5. "Correlated spin canting in ordered core-shell nanoparticle assemblies." Yumi Ijiri, KL Krycka, Ian Hunt-Isaak, Hillary Pan, J Hsieh, Julie A Borchers, James Jennings Rhyne, Samuel D Oberdick, A Abdelgawad, SA Majetich. Physical Review B.