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"Spin Current" Affairs in Boston
Satoru is a postdoctoral research associate in the laboratory of Prof. Nian Sun in the Department of Electrical and Computer Engineering. He is originally from Japan, and moved to California with his family in 1998. He received a Bachelor’s degree at the University of California, Irvine in 2008. Satoru completed his Ph.D. in Materials Science and Engineering at the Massachusetts Institute of Technology, under the supervision of Prof. Geoff Beach, in October 2013.
"Spin Current" Affairs in Boston
We commonly think of magnetism as a force that can attract or repel, but we’re able to harness this seemingly simple property to do much more. One important example is magnetic data storage; hard disk drives have made use of this technology, which has seen amazing advances over the years. If the future holds technology that makes our terabyte hard drives as obsolete as the floppy disks (which I used in high school), we need to keep pace with storage devices that consume less power, run at higher speeds, take up less space, and withstand more use. This requires new magnetic materials and a better understanding of their physical properties.
Northeastern is a hotspot for magnetism research, where a variety of materials and physics are investigated by many laboratories, including those headed by Profs. David Budil, Vince Harris, Don Heiman, Laura Lewis, and Carmine Vittoria. I have been fortunate to work as a postdoc in the laboratory of Prof. Nian Sun, which specializes in magnetic materials for high-frequency devices. Northeastern has been an ideal place for me to continue pursuing my research interests in magnetism (or what many call “spintronics”), expand my experimental skillset, and work with great students. In the following, I’d like to tell you a little bit of background information on spintronics and what my colleagues and I have been doing in this exciting research field.
Let’s start with the very simple concept that an “up” magnetized digital bit = “1” and a “down” magnetized digital bit = “0”. With these two magnetic letters we can spell out the digital language of binary. To read the magnetized bits, the conventional hard drive requires a moving sensor and a moving disk. Because mechanically moving parts require energy and are prone to breaking, a particularly attractive idea is to develop solid-state magnetic devices that can be read by a stationary sensor, while the digital bits in a stationary medium are shifted or rewritten by means of an electric current. We can shift or rewrite digital bits without moving parts by using a flow of electrons’ quantum angular momentum units, or spins: When this “spin current” encounters a magnetization in a magnetic material, it can rotate the magnetization.
This magnetization rotation by spin current is the key physics in electrically-controlled “spin-electronic” or “spintronic” devices, which may replace magnetic hard drives as well as some charge-based solid-state memories. Many researchers have been studying spin-current physics for over two decades, and this technology has most recently been used in the commercialized spin-transfer-torque magnetic random access memory. In the last few years, many of us in spintronics research have been investigating a new mechanism to generate a spin current, where an electric current passing through a thin film of heavy metal undergoes a scattering effect (called the “spin Hall effect”), allowing for many spins per electron and thereby more efficient magnetization switching.
Materials used in spintronics research are very thin, often just a few nanometers or sometimes only a few layers of atoms! Our research may be conducted on a very small scale, but it can have a huge impact on industry development. For example, findings from my former lab in 2013 have gained considerable interest among both academic and industrial researchers, and may lead the way to more efficient ways of storing data. The significance of my work in this field was also recently recognized earlier this year by Forbes’ 30 under 30, which nominated me as one of the up-and-coming researchers in the category of Science. Coming from a business magazine which often focuses on tech-startups and other entrepreneurial endeavors, it’s especially rewarding to see academic accomplishments being recognized.
Here at Northeastern, with the help of Ph.D. candidate Tianxiang Nan and other resourceful colleagues in the lab, I’ve set up new measurement techniques for probing spin current dynamics. I have also been very fortunate to work with highly motivated undergraduate engineering students. Recently, my colleagues and I have revealed how atomic-scale engineering affects high-frequency spin-current physics in composite thin films, and we’re on track to get to more important findings. My work has been further enriched by collaborations both within and outside of the university. For example, a collaborative project with the Air Force Research Laboratory has produced high-quality magnetic films with arguably the best resonant magnetic properties reported to date. Overall I expect our work to enhance the fundamental understanding of spin current physics and to bring these materials closer to practical applications in computing and telecommunications.
It takes hard work to succeed in any field, but I couldn’t have made it this far without the support of many people with whom I’ve worked along the way, especially my Ph.D. thesis advisor, Prof. Geoff Beach, and my colleague and friend, Dr. Charles Sing (who incidentally was also honored by Forbes’ 30 under 30 this year for his work on polymer science).
While being honored for my research by Forbes’ 30 under 30 was a milestone in my career, there are still many unanswered questions I’d like to pursue in future research. Resolving those questions will lead to materials with even more robust spin current effects, useful for devices with enhanced efficiency. Spintronics has grown tremendously in the last few years, and I intend to keep working in this area because I remain fascinated by what those spinning electrons can do.