At JST-CREST, our laboratory is researching device materials to dramatically improve the characteristics of magnetic tunnel junctions, which are representative of charge-spin coupled devices. A magnetic tunnel junction is a laminated element in which an insulating thin film is sandwiched between conductive thin films that have magnetic properties. Each layer is on the order of a few nanometers thick. When a voltage is applied to the conductors above and below the insulator, a current flows due to the quantum mechanical tunneling effect. It is also called a TMR element because it exhibits a tunnel magnetoresistive effect (TMR effect) in which the electrical resistance of the element changes depending on whether the magnetization (orientation of the magnetic poles) of the two upper and lower magnets is parallel or antiparallel. This element has been applied to magnetic sensors and magnetic heads of hard disks, and has become one of the spintronics devices indispensable to modern society. Recently, memory companies around the world, including Japan, are developing magnetoresistive random access memory (MRAM) that applies this technology. In addition, basic research on various artificial intelligence hardware using this is being advanced worldwide. The tunnel magnetoresistive effect is the most fundamental characteristic that determines the performance of these various applied products. In our laboratory, we aim to develop materials that exhibit a huge tunnel magnetoresistive effect, and we are pursuing original materials that can serve as insulating barriers for conductors and devices that exhibit magnetic properties. In addition, in collaboration with overseas and domestic research groups, we are promoting unique research and development, such as a device material development method that combines machine learning and physical property computer simulation, and an efficient device material search that incorporates Bayesian inference. We are here. For example, as a recent result, we have researched and developed a new magnetic material with a metastable phase that does not exist in nature, and have succeeded in obtaining excellent device characteristics.


Main achievements

Large tunnel magnetoresistance in magnetic tunnel junctions with magnetic electrodes of metastable body-centered cubic CoMnFe alloys,
T. Ichinose, J. Ikeda, Y. Onodera, T. Tsuchiya, K.Z. Suzuki, and S. Mizukami,
J. Alloys and Compounds, 960, 170750 (2023).
DOI: https://doi.org/10.1016/j.jallcom.2023.170750
Press Release：Researchers Discover Materials Exhibiting Huge Magnetoresistance
https://www.wpi-aimr.tohoku.ac.jp/en/achievements/press/2023/20230607_001633.html

Enhanced tunnel magnetoresistance in Mn-based perpendicular magnetic tunnel junctions utilizing antiferromagnetically coupled bcc-Co-based interlayerK.Z. Suzuki, T. Ichinose, S. Iihama, R. Monma, and S. Mizukami,
Appl. Phys. Lett. 118, 172412 (2021)
DOI: https://doi.org/10.1063/5.0042899

Lattice Softening in Metastable bcc (001) Ferromagnetic Layers for a Strain-Free Magnetic Tunnel Junction,
K. Elphick, K. Yoshida, T. Roy, T. Ichinose, K. Kunimatsu, T. Tsuchiya, K.Z. Suzuki, M. Tsujikawa, Y. Nagai, S. Mizukami, M. Shirai, and A. Hirohata,
Phys. Rev. Appl. 16, 054052 (2021).
DOI: https://doi.org/10.1103/PhysRevApplied.16.054052

Magnetic tunnel junctions with metastable bcc Co3Mn electrodes, K. Kunimatsu, T. Tsuchiya, T. Toy, K. Elphick, T. Ichinose, M. Tsujikawa, A. Hirohata, M. Shirai, and S. Mizukami,
Appl. Phys. Express 13, 0830007 (2020).
(Spotlight 2020)
https://iopscience.iop.org/article/10.35848/1882-0786/aba883

Fabrication of magnetic tunnel junctions with a metastable bcc Co3Mn disordered alloy as a bottom electrode,
K. Kunimatsu, T. Tsuchiya, K. Elphick, T. Ichinose, K. Z. Suzuki, A. Hirohata, and S. Mizukami,
Jpn. J. App. Phys. 58, 080908(R) (2019).
https://iopscience.iop.org/article/10.7567/1347-4065/ab2f96