INSIDE the Laboratory

Information Devices Division

Materials Functionality Design Laboratory

Masafumi Shirai, Professor
Kazutaka Abe, Assistant Professor
Masahito Tsujikawa, Assistant Professor

http://www.shirai.riec.tohoku.ac.jp/

The research targets of the laboratory are as follows: (1) theoretical analyses of quantum phenomena which appear in materials for next-generation information devices, (2) computational design of materials which possess new functionalities for improvement of device performance, and (3) development of innovative design procedures based on the knowledge of materials science and information technology. Recent research activities are described below.

1. Theoretical study on transport properties of giant agnetoresistive devices

We investigated the spin-dependent transport properties of giant magnetoresistive devices with highly spin-polarized Heusler alloys as electrodes on the basis of first-principles calculations. We found that the matching of the electronic structure (Fermi surface) between the electrode and spacer materials predominantly determines interfacial resistance. In particular, Ag and Ag-Mg spacers are promising for improving the magnetoresistance of the devices.

2. Theoretical design of new permanent magnets without rare elements

The development of new permanent magnets is required due to the high cost and limited reserves of rare-earth elements. We carried out theoretical design of magnet materials possessing large magnetization and high magnetic anisotropy, focusing on Fe-Co, Co-Ni, Fe-Ni, Mn-Ga, Mn-Ge alloys. We found that the doping Ti, V, Al, or Si into FeNi stabilizes the L10-ordered phase, and that the doping B, C, or N enhances uniaxial magnetic anisotropy.

3. Theoretical study on metallization and superconductivity of hydrides

Hydrides have been predicted to have high superconducting transition temperatures (Tc) once they are metallized under compression. We have so far predicted several metallic hydrides of B, Ge, Sb, and Bi in the range from 100 to 350 GPa, which exhibit superconductivity. The values of their Tc are rather high for superconductivity driven by electron-phonon coupling; especially, the Tc' s of the B and Ge hydrides are estimated to reach about 100 K.

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