February 10, 2025
Keio University
Nihon University
Chuo University
A research group, including Takumi Funato, a project promoter at the Advanced Science Research Center, Japan Atomic Energy Agency (then a Project Assistant Professor at the Spintronics Research and Development Center, Keio University Global Research Institute), Shunichiro Kinoshita, a researcher at the Natural Science Research Institute, College of Humanities and Sciences, Nihon University, Norihiro Tanahashi, a project associate professor at the Graduate School of Science, Kyoto University (then an assistant professor at the Faculty of Science and Technology, Chuo University), Professor Makoto Nakamura of the Faculty of Science and Technology, Chuo University, and Associate Professor Mamoru Matsuo of the Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, has theoretically demonstrated that a magnetic flow is generated from "differential rotation," where the angular velocity differs from place to place within a substance.
About 100 years ago, Einstein discovered the "magneto-rotational effect." This phenomenon, in which a magnet undergoes rotational motion when its magnetization is changed, demonstrates that magnetism and rotation are mutually convertible. This discovery is known as a monumental achievement, showing that the origin of magnetism in matter lies in the quantum mechanical rotation of electrons, called "spin." It is also his only experimental discovery, for which Einstein himself conducted the demonstration experiment.
In recent years, with advances in nanotechnology, this magneto-rotational effect has been garnering renewed attention. It is being utilized as a method to generate "spin current," a flow of magnetism, in materials designed at the nanoscale, and is being actively researched for next-generation spintronics device applications.
Previous research has generated spin currents by injecting sound waves into solids to induce local rotational motion or by utilizing the vortex motion of liquid metals. However, these methods were thought to require "vorticity," similar to a swirling vortex of water.
In this study, we have theoretically demonstrated a new mechanism that can generate spin current solely from differences in angular velocity, without relying on the "vorticity" of rotational motion. This opens up a path to creating spin currents even in environments where their generation was previously considered difficult. Technology based on this new principle is expected to enable applications in a wider variety of materials and devices than ever before, contributing to the further development of the spintronics field.
The results of this research were published in the American Physical Society's journal "Physical Review B" on February 6, 2025, and were selected as an Editors' Suggestion.
For the full press release, please see below.