磁気冷凍法による高効率な水素液化の実現に、多重相転移を持つ磁性体を利用し、広い温度範囲で磁気熱量効果を増大できる可能性がある。本研究では、(ErDy)NiAl系, (Er,Dy)Al2系, Er(Co,Ni)2系, Er(Co,Cu)2などで希土類、遷移金属の置換でエントロピー変化を制御した物質の合成を行った。磁化、磁場中比熱、断熱消磁測定などにより磁気熱量効果を評価し、実用となる磁気冷凍用磁性材料の研究を進めた。これまでの単純な常磁性-強磁性・反強磁性転移だけでないエントロピー制御性を持つ磁性体の特性を明らかにした。また、金属間化合物以外にも硫化物、酸化物などの磁性体の特性を明らかにした。
Magnetic refrigeration method makes use of the magnetocaloric effect (MCE) where some magnetic materials exhaust or absorb heat by applying or removing external magnetic fields. MCE is induced by the internal magnetic entropy change of magnetic material, thus magnetic refrigeration can operate an ideal cycle like Carnot.
In this research, we investigated new magnetic materials that will be useful for hydrogen magnetic refrigeration. It is possible to control temperature and magnetic field dependence of the MCE using magnetic materials with multiple transitions. Magnetic materials of intermetallic compounds such as (ErDy)NiAl, (Er,Dy)Al2, Er(Co,Ni)2, Er(Co,Cu)2 were synthesized. Magnetic and thermal properties of those compounds were measured in order to evaluated MCE. MCE results for oxides, sulfide that have rare-earth elements were also studied as useful materials.
多重相転移磁気熱量効果を利用した新規磁性体による高効率水素磁気冷凍の研究
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