Graduate School of Engineering
Department of Materials Science

Permanent Magnets

Permanent magnets are essential materials for us and widely used in many applications such as motors. It is well known that the rare-earth permanent magnets (Nd-Fe-B, Sm-Fe-N, Sm-Co, etc) show excellent magnetic properties. In our laboratory, we are focusing on development magnetic properties of the rare-earth permanent magnets, and are trying to develop new permanent magnet.

We obtained high performance Zn-bonded Sm-Fe-N magnets. The Sm-Fe-N bulk magnets with a low oxygen content were prepared by the Spark-Plasma-Sintering, and it shows high energy products of 179 kJ/m³ (Fig. 1).

Electromagnetic wave absorbers

Recently, the use of GHz-range electromagnetic wave has been increasing, because of their large data transmission. 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.

We are focusing on the application of magnetic materials to electromagnetic wave absorbers. We developed amorphous Fe-B and Ni-Zn ferrite composite powders, and polymer composites of the Fe-B and Ni-Zn ferrite powders showed a higher relative permeability and good microwave absorption property (Fig. 2).

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 (E_F). 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, shch as Co₂(Cr,Fe)Al, Co₂FeAl_0.5Si_0.5 and so on, and TMR with a Heusler alloy film was first observed. The maximum TMR with the full-Heusler alloy film at RT was observed to be around 400% (Fig. 3).