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Professor:Ryuji Tamura

Our research covers various metallic materials such as “quasicrystals”, “compounds made of icosahedral clusters”, “exchange spring magnets”, “metallic glasses” and “alloy catalysts”. The Nobel prize in chemistry in 2011 was dedicated to the discovery of quasicrystals, however, many fundamental issues concerning the stability, property and potential applications of quasicrystals have not been clarified yet. For icosahedral cluster compounds, new interesting phenomena which have not been observed in normal metallic alloys have been discovered. Spring magnets, metallic glasses and alloy catalysts are expected for future materials used for motors in electrical vehicles, medical surgery tools and purification of toxic gases emitted from automobiles, respectively.

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Example study

“Research on nondiffusive order-disorder transitions in alloys”

Quasicrystals and their crystalline approximants are composed of icosahedral clusters. Our aim of the research is to understand the intrinsic property of the icosahedral cluster by investigating the behaviours of atoms, electrons and spins. Recently, it has been discovered that a disordered tetrahedron inside an icosahedral cluster in some crystalline approximants becomes orientationally ordered at a very low temperature of 110 K. This is a new type of solid-solid transition which has never been observed before. We are currently investigating this novel transition to answer why and how it occurs at such a low temperature.

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“Research on the behaviour of spins on an icosahedral cluster”

Since an icosahedron is made of 20 regular triangles, localized spins on an icosahedron are geometrically frustrated. The aim of this research is to understand the behaviour of spins on an icosahedron inside metallic alloys. Previous works on magnetic quasicrystals and crystalline approximants have shown that they become spin glass at the lowest temperature. However, our recent work has shown that spins on an icosahedron can form long-range order in some crystalline approximants. The magnetic behaviour of spins on an icosahedron is studied by magnetization measurements as well as specific heat measurements. The magnetic structure is investigated by synchrotron X-ray resonant magnetic scattering.

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“Synthesis of nanocomposite magnets”

When a hard magnet like a Nd-Fe-B magnet and a high magnetization magnet such as α-Fe are mixed on a nanoscale, the two phases are magnetically coupled by the exchange interaction and behave as a single phase magnet with strong coercivity as well as high magnetization. Such nanocomposite magnets are promising materials as next generation hard magnets. They are also attractive in view of sustainability because the usage of rare-earth elements can be substantially reduced. In our laboratory, various nanocomposite magnets are synthesized by means of melt-quenching, mechanical milling as well as hydrogenation and dehydrogenation process in order to apply them for future hard materials such as those used in electrical vehicle, etc.

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