[No. 73] Hideo Kaiju

I spent a total of eight and a half years as a student here at Keio University: four years as an undergraduate, one and a half years in the master's program, and three years in the doctoral program. Looking back on those eight and a half years, I strongly feel that the "education," "research," and "life lessons" I gained at Keio University were truly invaluable. In this article, I would like to reflect on these eight and a half years, share some events and experiences from my undergraduate and graduate school days, and also briefly introduce my current research.

After enrolling in the Faculty of Science and Technology at Keio University, I went through "Gakumon 1," a physics-oriented academic category, and in my second year, I advanced to the Department of Applied Physics and Physico-Informatics. At the time, the department had just been established, so I honestly didn't know much about what kind of department it was. However, I was originally interested in both "physics" and "information," and at the department information session, Professor Shiiki used "Dragon Quest" to carefully explain the department, and Professors Kohei M. Itoh and Masanori Matoba enthusiastically recruited us. The lively and positive atmosphere convinced me to choose the Department of Applied Physics and Physico-Informatics. From that moment, I was determined to do my best as a member of the "first graduating class" of this "Butsujo" (the department's nickname).

Once classes in the Department of Applied Physics and Physico-Informatics began, a series of enjoyable days followed. The classes covered a wide range of fields that I was interested in, from solid-state engineering, quantum mechanics, magnetism, statistical mechanics, and electromagnetism to electrical and electronic circuits, control engineering, and programming languages. I could tangibly feel myself growing. In the end, I graduated after four years without missing a single class, and for me, it was a very fulfilling undergraduate life with a great sense of accomplishment.

After graduating from Keio, I went on to the master's program at the same university's graduate school. I joined the "Shiiki Laboratory," which I had been a part of since my fourth year as an undergraduate. At the entrance to the Shiiki Laboratory, there was a sign that read, "The Laboratory of Magnetism (Jisei) and Life (Jinsei)," and indeed, I was about to learn about both "magnetism and life."

Professor Shiiki gave me a very interesting research theme: "Impedance Characteristics of Spin-Tunneling Junctions." Initially, I approached the research thinking, "I studied hard in university, so if I just continue to work hard on my research, it will go well." But it wasn't that simple. No matter how many times I tried, I couldn't fabricate the devices, and even when I did, they didn't show good characteristics. This was the cycle at the beginning. Despite his busy schedule, Professor Shiiki was watching over this situation closely. He then taught me the ABCs of "research" and "life." There are too many lessons to list them all here, but he taught me from scratch about things that are absolutely essential, especially in group research, such as "the importance of human relationships," "how to plan to achieve a goal," and the mindset that "second place is the same as last—aim for first!"

Thanks to Professor Shiiki's advice, my research finally got on track, and during my master's program, I was able to discover the magneto-impedance effect in spin-tunneling junctions. This allowed me to complete my master's degree in one and a half years and also be selected as a Research Fellow of the Japan Society for the Promotion of Science. In the doctoral program, I proposed oscillation-controlled magnetic sensing using spin-tunneling junctions and succeeded in its demonstration. All of this was thanks to Professor Shiiki's detailed guidance. He also meticulously taught me many other things, from how to write international academic papers and give effective presentations to how to write patents. Incidentally, a patent that I filed jointly with Professor Shiiki has already been granted through the Keio University Intellectual Property Center. I secretly believe that there are probably no other students who receive such dedicated guidance from a university professor. And although there were many twists and turns, I was able to compile the research results I had accumulated one by one into my doctoral dissertation, and I felt an unparalleled sense of accomplishment.

Currently, at the Research Institute for Electronic Science, Hokkaido University, I am conducting research on a new type of nanoscale junction device where molecules are sandwiched between the edges of magnetic thin films. It is an advanced version of a spin-tunneling junction—a novel quantum device that integrates "spin," "molecules," and "nano." Although it is challenging, it is an unexplored field of research, and I believe many interesting physical phenomena are hidden within it.

Recently, my research was featured in the European news outlet “Nanotechweb” . While I encourage you to refer to the link for details, I will briefly introduce the content here. To fabricate the aforementioned quantum device—that is, the ultimate nanoscale junction—I proposed a new method in which the edges of thin films are made to face each other. In this method, the junction area is determined by the thickness of the thin film. For example, using a 10 nm thick film can create an ultra-small junction of 10 nm × 10 nm. Last year, I succeeded in demonstrating this for the first time.

Once this technology is established, it opens up many exciting possibilities. For example, by sandwiching molecules between the edges, we can expect to see ultimate nano-molecular processing and giant switching effects. This will lead to the creation of Beyond CMOS switching devices. Furthermore, if the thin film is made of a magnetic material, we can also expect spin injection at the nanoscale and a giant magnetoresistance effect. This will lead to applications in next-generation magnetic head devices and magnetic sensors. Thus, this integrated device of "spin," "molecules," and "nano" is a very attractive and promising device with significance in both physics and engineering. Last fall, my project was also selected for the JST PRESTO program, " Materials and Processes for Innovative Next-Generation Devices ." I hope you will take a look at this as well, but I strongly believe that I have been able to come this far because of the "education," "research," and "life lessons" I received at the Faculty of Science and Technology, the Department of Applied Physics and Physico-Informatics, and the Shiiki Laboratory at Keio University. Moving forward, I intend to continue pursuing groundbreaking and innovative research, holding dear the many invaluable experiences I gained at Keio University.