Spin Conversion Research towards Novel Spintronic Functionalities
Spin conversion is a generic term for all the conversion phenomena among various quasi-particles, i.e., electrons, magnons, phonons, and photons. The spin conversion manifests as a variety of spintronic phenomena, including the direct and inverse spin Hall effects (SHEs), Rashba Edelstein effects at the interface with broken spatial inversion symmetry, or the surface states of topological insulators.
Spin currents primarily mediated these conversion phenomena as a flow of angular momenta; however, recent studies revealed that orbital degree of freedom also contributed to the conversion phenomena as orbital currents, similarly to the spin currents. The orbital version of Rashba Edelstein effects has been observed to generate diffusive orbital currents that effectively exert spin torque on adjacent magnetic layers.
On the other hand, spintronics has recently evolved in the direction where one tries to benefit from the topological electronic nature of the materials. Chiral antiferromagnets, classified into Weyl semimetals, draw significant attention from the spintronics community, showing peculiar spin Hall effects with time-reversal asymmetry and distinctive antiferromagnetic domain wall dynamics.
In this seminar, I will discuss the recent evolution of spin conversion studies toward novel functionalities related to orbital currents and Chiral antiferromagnets.
YoshiChika Otani received the B.S., M.S., and Ph.D. degrees from Keio University in 1984, 1986, and 1989. He was a research fellow (1989–1991) at the Physics Department of Trinity College Dublin, the University of Dublin, and a researcher (1991–1992) at the Laboratoire Louis Néel, CNRS, France. He was an assistant professor (1992–1995) at the Department of Physics, Keio University; an associate professor at the Department of Materials Science, Graduate School of Engineering, Tohoku University (1995–2002); and became a team leader (since 2001) of the Quantum Nano-Scale Magnetics Research Team at FRS-RIKEN. In 2004 he became a professor at ISSP, the University of Tokyo. Since 2013, he has also been a team leader of the Quantum Nano-Scale Magnetism Research Team at CEMS-RIKEN.
Prof. Otani has published over 350 technical articles in peer-reviewed journals, including book chapters and review articles, and has given more than 100 invited and plenary presentations at international conferences. He has coordinated the Japanese MEXT supporting the 5-year “Nano Spin Conversion Science” project during 2014 to 2019 to elucidate the interconversion mechanisms among phonon, photon, magnon, and electrons. He was also a committee member of C.9 magnetism of the International Union of Pure and Applied Physics from 2011 to 2017 and vice chair from 2018 to 2021. He is a member of the IEEE Magnetics Society. Since 2022, he has been heading the Franco-Japanese research project developing the “magnon-phonon transducer” as a LANEF chair of Excellence at the University of Grenoble Alpes.