High-Quality-Magnetic Materials Fabricated by Cluster-Assembling

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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.