Super-spin glass with hierarchical structure aimed for a brain-type memory

阐明了作为随机磁系统原型的分级结构超自旋玻璃和无定形氧化物磁体的磁学基本原理。对于前者，制备了介孔二氧化硅微粒与介孔中析出的磁铁矿纳米晶的聚集态。法拉第效应测量表明，该材料在室温下表现出超顺磁性。对于非晶态氧化物磁体，同时含有铁和稀土元素的氧化物玻璃表现为自旋玻璃或超自旋玻璃转变，而非晶态EuZrO_3薄膜则表现为伴随铁磁转变的重入自旋玻璃转变。这些磁性相变的机制已被阐明。

Fundamentals of magnetism have been clarified for super-spin glass with hierarchical structure and amorphous oxide magnets which are prototype of random magnetic systems. For the former, an assemblage state of mesoporous silica microparticles with maghemite nanocrystals precipitated in the mesopores has been fabricated. The Faraday effect measurements reveal that the material show superparamagnetism at room temperature. As for the amorphous oxide magnets, oxide glasses containing both iron and rare-earth elements exhibit spin glass or super-spin glass transition, while amorphous EuZrO_3thin film shows re-entrant spin glass transition accompanied by ferromagnetic transition. The mechanism of these magnetic phase transitions have been elucidated.