Graduate School of Engineering
Department of Materials Science

Materials and Devices for Information Technology
Spin-electronics materials (Prof. Sugimoto)

Research Topics

Half-metallic Ferromagnets

There has been growing interest in highly spin-polarized ferromagnets, so-called half-metallic ferromagnets (HMF), which have a band gap for one spin subband at the Fermi level (EF). Thus spin polarization of conducting electrons in the HMF exhibits 100%, while transition metal ferromagnets (Fe, Co and Ni) possess spin polarization of 40~50%. The HMFs lead to a creation of a new field of spintronics, which enables to inject electron spins from a ferromagnetic metal into a semiconductor with high efficiency, in addition to the enormous increase of tunneling magnetoresistance (TMR). We are focusing on full-Heusler alloys predicted to be half-metallic ferromagnets with high Currie temperatures, especially Co2(Cr,Fe)Al alloys. The maximum TMR with the full-Heusler alloy film at RT was observed to be 19%, which is the first observation of TMR with a Heusler alloy film.

Electromagnetic wave absorbers

Recently, the use of GHz-range electromagnetic wave has been increasing, because of their large data transmission. In particular, the number of electromagnetic devices such as handy phone systems (PHS), wireless LAN and Ultra Wide Band (UWB) etc, in which the microwave in GHz-range is used, has increased rapidly. This increase, however, has brought very serious electromagnetic interference (EMI) problems. Therefore, electromagnetic wave absorbers for this frequency range have been paid much attention as one of countermeasures to these EMI problems. In our laboratory, we are focusing on the application of magnetic materials to electromagnetic wave absorbers.

Fig. 1:Mgnetoresistance curve at RT for spin-valve-type magnetic tunneling junction with Co2(Cr0.6Fe0.4)Al, which are known as to be a half metal. Left side inset shows TMR curve at 5K.

Fig. 1:
Mgnetoresistance curve at RT for spin-valve-type magnetic tunneling junction with Co2(Cr0.6Fe0.4)Al, which are known as to be a half metal. Left side inset shows TMR curve at 5K.

Fig. 2:Variation of R.L. on the frequency of 60~80 mass% BaFe9.0(Ti0.50.5)3.0O19 ferrite-resin composite

Fig. 2:
Variation of R.L. on the frequency of 60~80 mass% BaFe9.0(Ti0.50.5)3.0O19 ferrite-resin composite