Research Projects -
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Magnetic and Optical properties of artifical superlattice
Grant number：05453079 1993 - 1994
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for General Scientific Research (B)
MIURA Yoshinari, FUJII Tatsuo, OSAKA Akiyoshi
Grant amount：\7100000 （ Direct expense: \7100000 ）
Magnetic superlattices including ferromagnetic and diamagnetic layrs bring interesting properties such as the giant magnetoresistance and the mangneto-optical effects. On the other hand, it is well known that titanium oxides change their properties sensitively with their metal to oxygen ratios.
Fe_3O_4/Mo (M=Mg, Co) superlattice films having various thickness combinations of the individual Fe_3O_4 and Mo were prepared by an activated reactive evaporation (ARE) method. Stoichiometric and monstoichiometric titanium oxide films were also epitaxially formed on alpha-Al_2O_3 (0001) substrates by ARE method. The summarized results are as follows :
1. Epitaxial growths and artificial modulations of (111) -and (100) -orientated Fe_3O_4/Mgo films deposited on (0001) -faced alpha-Al_2O_3 and (100) -faced Mgo single crystaline substrates, respectively, were confirmed. The saturation magnetization of each film at 5K was about 85-100 emu/g, being nealy consistent with that of the Fe_3O_4 bulk. However, with increasing temperature the magnetizations decreased linearly in proportion to 1/T below 40K.
2. For Fe_3O_4/CoO film the lattice spacing along the growth direction was contracted for the CoO layr but expanded for the Fe_3O_4 layr probably due to the lattice mismatch between these layrs. The magnetostriction of CoO layrs induced in-plane and perpendicular magnetic anisotropy in (100) -and (111) -oriented superlattices, respectively. Strong magnetic coupling between Fe_3O_4 and CoO layrs made the Neel temperature of the CoO layr higher and showed the ferrimagnetic/antiferromagnetic exchange anisotropy.
3. Titanium di-and sesquioxide films were epitaxially grown on (0001) alpha-Al_2O_3. Films prepared at Po_2*2.0*10^<-4> Torr were stoichiometric (100) -oriented rutile of TiO_2. AtP_<02>=0.6*10^<-4> Torr, on the other hand, (001) -oriented Ti_2O_3 was formed and an electrical transition was clearly detected at about 400K. -
スパッタ法による歪み酸化鉄薄膜の磁気光学特性
Grant number：05855130 1993
日本学術振興会 科学研究費助成事業 奨励研究(A)
藤井 達生
Grant amount：\1200000 （ Direct expense: \1200000 ）
rfマグネトロンスパッタ法を用い、サファイア(alpha-Al_2O_3)単結晶基板上に酸化鉄(alpha-Fe_2O_3)薄膜を作製した。酸化鉄(alpha-Fe_2O_3)は約250Kにモ-リン転移と呼ばれるスピン相転移を持ち、その前後でスピン軸がc面内からc軸方向へと90°変化することが知られている。しかし、単結晶基板上に成長した酸化鉄薄膜の場合は、基板界面におけるミスフィットが結晶格子に歪みを与える結果、スピン相転移はそのスピン軸、転移温度ともバルクに比べ、異なった振舞を示すことが期待される。
alpha-Al_2O_3(102)単結晶基板上にエピタキシャル成長したalpha-Fe_2O_3(102)について、メスバウアー分光測定を行なった結果、スピン転移温度は400Kへと大きく上昇しており、しかもスピン軸はc軸から<102>方向へと変化していた。そこで4軸回折計による薄膜のX線構造解析を試みた結果、a軸長は約0.5%減少し、一方、c軸長は約0.2%増加していた。一方、alpha-Al_2O_3(001)単結晶基板上にエピタキシャル成長したalpha-Fe_2O_3(001)について、メスバウアー分光測定及びX線構造解析を行なった結果、スピン相転移は極低温(2K)に至まで観測されず、逆にa軸長が約0.3%増加し、c軸長が約0.5%減少していた。従って、得られた酸化鉄薄膜のスピン相転移の変化は、異方的な歪みが原因で生じたものと推論できる。得られた薄膜の磁気光学特性については、現在まだ検討中である。 -
Preparation of Fact-Ion Conductive Thin Films as nano-sized Battery Electrolytes
Grant number：04650705 1992 - 1993
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for General Scientific Research (C)
OSAKA Akiyoshi, FUJII Tatsuo, NANBA Tokurou
Grant amount：\1870000 （ Direct expense: \1870000 ）
The present research was exploited based on a demand for developing optical memory materials and electrolytes for fine scale solid batteries. Thin films of the systems F-O-Si-Pb and CuI-MoO_4-P_2O_5 were prepared with an rf-sputtering technique and their microstructure, electrical conductivity and phase change due to laser irradiation.
1. Amorphous thin films of the system F-O-Si-Pb
Amorphous thin films of the system F-O-Si-Pb were rf-sputtered under the conditions : the Ar chamber pressure : 0.06-0.07 Torr, rf-power : 100W, sputtering time : 45min. X-ray photoelectron spectra showed that the fluorine atoms were homogeneously distributed in the films but the ratio F-Si/F-Pb decreased in the direction from the surface to the film-substrate interface. The results were accounted for by an increase in non-bridging oxygen due to a reaction Si-O-Si->Si-F+Si-O^-. Irradiation of 3mW He-Ne laser beam (lambda=632.8nm) for 1/500s induced crystallization of a quartz in the area of 11mum radium, independent of the fluorine content, but not induced an expected PbF2 phase of high conductivity. Fluorine ionic conductivity obeyed an Arrhenius type temperature dependence with sigma=1.1x10-5 S/cm at 500K, two orders of magnitude larger than the corresponding bulk glass, and activation energy of 106.5kJ/mol.
2. Amorphous thin films of the system CuI-MoO_4-P_2O_5
A target of a composition 25CuI・25Cu_2O・25MoO_4・25Cu_3(PO_4)_3 was rf-sputtered with the same conditions above to prepare amorphous films. They had a particular microstructure and were insulators below 550K with conductivity as small as 10^<-8> S/cm. The increase in the rf-power grew cubic particles of gamma-CuI while a large fraction of Cu atoms were divalent. The laser irradiation dug holes of 8mum in diameter even at 1/500 s and the holes grew to 12 at 1s irradiation, whereas no crystallization was observed.