RESERCH FIELD

Since its first fabrication in 1956, ferrimagnetic garnet has played a central role in magneto-optics and spin dynamics thanks to its high transparency to visible light and low magnetization damping. However, these properties are tied to its insulating nature, hampering the electrical control of magnetization with conventional spintronics technology such as spin-transfer torque. Recently, breaking through technology comes out from spin-orbitronics, which leverage spin-orbit interactions. Along with cutting-edge growth technologies, current-induced magnetization switching in ferrimagnetic garnet has been demonstrated. Since ferrimagnetic garnets are not found in nature, the advance in its fabrication methods have driven progress in this research field. We have developed a method to produce ultra-thin films of ferrimagnetic garnet on an unprecedented scale, contributing to the evolution of ferrimagnetic garnet materials engineering in the spin-orbitronics era. 

Semiconductor silicon, recognized as the king of electronics materials that underpins today’s information society, is also recognized as a vital material in spintronics. In solid-state materials, the spin current of conduction electrons decays over a distance determined by the spin diffusion length. Silicon has an exceptionally long spin diffusion length among three-dimensional elemental materials, thanks to its crystaline spatial inversion symmetry and the light elemental nature, bringing tiny spin-orbit interaction. To generate a spin current in silicon, electrodes with a finite spin polarization in the electron's density of states are required. Furthermore, since every electronic device requires an ohmic contact (an electrode with good electrical conductivity) to maximize device performance. Thus, a low-resistance and spin-polarized material is essential for silicon spin devices. By controlling the work function of magnetic materials, we have developed a new electrode material that enables high-efficiency generation of spin-polarized currents in semiconductor silicon for the first time worldwide. 

Spin caloritronics is a term that combines 'calorie,' the unit of heat, with 'spintronics' and represents a field of study that explores the interactions between thermoelectric properties and spin angular momentum. Since the 2008 report on the spin Seebeck effect, numerous novel phenomena have been reported in which spin currents are generated from heat. We are researching phenomena such as the spin-dependent Seebeck effect, which is the spin-current analog of the Seebeck effect, a representative thermoelectric conversion phenomenon. By generating spin currents from a ferromagnetic material to a non-magnetic material using heat, we focus on the potential to recycle Joule heat generated in semiconductor devices like CMOS through spin currents. This approach could not only improve spin injection efficiency but also contribute to the efficient use of energy.