High-Quality-Magnetic Materials Fabricated by Cluster-Assembling

我们希望建立新的范例，从纳米级簇中制造功能材料，这对应于功能元素的单位。我们三年的研究活动总结如下。1)利用飞行时间质谱仪设计并构建了激光汽化型团簇沉积系统。质谱分析表明，由7、13、15、19个原子组成的团簇对Fe、Ti、Ta、Nb和Zr具有一定的幻数效应，而对Ni和co没有明显的幻数效应。其中Fe_<13>O_8、Fe_<43>O_<20>丰度较强。第一原理分子轨道计算证实了这一特征。3)等离子体-气体凝聚产生的单色散Co团簇在约9 nm处检测到超顺磁性到铁磁性的转变。4)钴包覆钴团簇的组装体表现出非常大的隧穿型磁阻。对数电导率呈T^<-1>依赖性，表明簇大小的单色散性和CoO层厚度的均匀性。5)观察了Co簇组装膜的XAFS、MCD和磁光Kerr光谱。在团簇表面形成两层单层CoO。在内部金属Co芯中，fcc在团簇尺寸上占主导地位，d= 6 nm。随着d从6 nm增加到13 nm， hcp的体积分数增加。磁光克尔效应在低波长区域得到增强。

We would like to establish the new paradigm, functional-material-fabrication from nano-scale clusters, which correspond to units of functional elements. The summaries of our resarch activities for three years are as follows.1) We designed and constructed a laser-vaparization type cluster deposition system with a time-of- flight mass spectrometer. The mass-spectrometric studies of transition metal clusters indicate that the clusters consiting of 7,13,15,19 atoms are magic numbers for Fe, Ti, Ta, Nb and Zr, while no marked magic number effect for Ni and Co.2) We analyzed the Fe-oxide cluster formation process by mass-spectrtometry. The abundnances of Fe_<13>O_8, Fe_<43>O_<20> are much stronger the others'. This feature is confirmed by the first principle molecular orbital calculations.3) Superparamagnetic to ferromagnetic transition is detected at around 9 nm for mono-dispersive Co clusters produced by plasma-gas-condensation.4) The assemblies of CoO coated Co clusters show very large tunneling type magnetoresistance. The logarithmic conductivity shows T^<-1> dependence, indicating monodispersivity in the cluster size and uniformity of the CoO layer thickness.5) XAFS, MCD and Magneto-optical Kerr spectra were observed for Co cluster assembled films. Two monolayered CoO is formed at the cluster surface. In the inner metallic Co cores , fcc is predominant for the cluster size, d= 6 nm. With increasing d from 6 to 13 nm, the volume fraction of hcp increases. The magneto-optical Kerr effect is enhanced at the low wave length region.