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Okayasu, Satoru; Ono, Masao; Nishio, Taichiro*; Iguchi, Yusuke*; Mashimo, Tsutomu*
Defect and Diffusion Forum, 323-325, p.545 - 548, 2012/04
Times Cited Count:0 Percentile:0.01Atomic sedimentation in solid occurs under mega-gravity treatment. As the result, partially melt-growth in -phase of BiPb-alloy occurs. Small difference of densities between fully hcp structure of BiPb and that of partially defected BiPb are enhanced under mega-gravity, and cause the separation of the -phase. Superconducting properties differs between the separated two phases.
Nishio, Taichiro*; Okayasu, Satoru; Suzuki, Junichi; Kokubo, Nobuhito*; Kadowaki, Kazuo*
Physical Review B, 77(5), p.052503_1 - 052503_4, 2008/02
Times Cited Count:16 Percentile:56.7(Materials Science, Multidisciplinary)We have observed the magnetic field distribution of a vortex generated in amorphous ()-MoGe thin films with various thicknesses () (, where is the penetration depth) with a scanning SQUID microscope. From analyses of the field distribution as functions of the film thickness and temperature, it is found that an effective in-plane penetration depth () extends with descreasing d, in accordance with the Pearl's prediction =2/. Temperature dependence of is also consistent with the two-fluid model involving the Pearl's prediction.
Okayasu, Satoru; Nishio, Taichiro; Ono, Masao; Mashimo, Tsutomu; Tanaka, Yasutomo*; Iyo, Akira*
Physica C, 445-448, p.245 - 248, 2006/10
Times Cited Count:1 Percentile:6.65(Physics, Applied)Vortex imagings of Tl-2223 thin film are achieved below Tc with a scanning SQUID microscope. Vortex arrangements are almost the same just below Tc, indicating the existence of strong pinning centers in the sample. The origin of the strong pinning centers comes from the morphological inhomogeneity on the surface.
Okayasu, Satoru; Nishio, Taichiro*; Ono, Masao; Mashimo, Tsutomu; Tanaka, Yasumoto*; Iyo, Akira*
Physica C, 437-438, p.239 - 241, 2006/05
Times Cited Count:3 Percentile:18.02(Physics, Applied)Pinning properties of superconducting material Tl-1223 thin film are investigated. Vortex images are compared between a pristine and high-energy gold ion irradiated sample. This comparison implies which pinning center is effective for this material between large pinning centers and columnar defect. Large pinning centers are better for this material.
Nishio, Taichiro; Okayasu, Satoru; Suzuki, Junichi; Kadowaki, Kazuo
Physica C, 412-414(Part1), p.379 - 384, 2004/10
We have studied the vortex states in a meoscopic superconductor with geometrical constraints such as disks, triangles, squares, etc. with dimensions between 30-50m using a scanning SQUID microscope (SQM2000,Seiko Instruments Inc.). The sample was fabricated by electron lithography and Focused Ion Beam (FIB) techniques. Quantized vortices enter into a mesoscopic superconductor discretely as a function of magnetic field accompanied by the sequential step-wise jump of magnetization of the superconductor. Quantitative as well as qualitative analyses of spatial vortex arrangement as a function of the number of vortices will be shown in comparison with the recent theoretical predictions.
Suzuki, Junichi; Kadowaki, Kazuo; Hata, Yoshiaki*; Okayasu, Satoru; Nishio, Taichiro; Kakeya, Itsuhiro*; Odawara, Akikazu*; Nagata, Atsushi*; Nakayama, Satoshi*; Chinone, Kazuo*
Teion Kogaku, 38(9), p.485 - 492, 2003/09
no abstracts in English
Okayasu, Satoru; Ono, Masao; Nishio, Taichiro*; Iguchi, Yusuke*; Mashimo, Tsutomu
no journal, ,
We prepared a gradient composite superconductor alloy BiPb under mega-gravity field at 130 C for 100 hours. The prepared sample is separated into four parts along the gravity field direction, A) a Pb-rich phase with a almost constant molar proportion between Bi and Pb (3:7), B) a gradient composite mole ratio phase (the average mole ratio near by Bi:Pb=4:6), C) another gradient composite mole ratio phase with a different crystal structure to B), D) a bismuth-precipitated phase. We investigated the vortex state of this gradient superconducting sample with a scanning SQUID microscope. It is strange that no vortex can be found in the B)-phase, and the B)-phase act as a type-I superconductor. The differences among the superconducting phases can be explained by these of the pinning energies or by these of the superconducting condensation energies at individual phases.
Okayasu, Satoru; Ono, Masao; Nishio, Taichiro*; Iguchi, Yusuke*; Mashimo, Tsutomu
no journal, ,
no abstracts in English
Okayasu, Satoru; Ono, Masao; Nishio, Taichiro*; Iguchi, Yusuke*; Mashimo, Tsutomu
no journal, ,
Sedimentation of atoms can be caused under mega-gravity field even in solid. A composition-graded structure can be formed with the preparation in multi-component condensed matter. In this study, we performed a mega-gravity preparation (110 G, 130C, 100h) on a thin plate sample (0.7mm in thickness) of intermetallic superconducting compound BiPb. After the preparation, a visible four-layered structure appeared indicating different microscopic structures. In the mid two layers, the composition-graded structures were achieved. To investigate the superconducting states of each layer, direct vortex observations are accomplished for each layer with a scanning SQUID microscope. No vortex can be observed in the one of the composition-graded layer at higher gravity region. On the other hand, vortices can penetrate into other three layers. Each layer shows different superconducting property. We discuss the differences of the vortex states at the individual layers.
Okayasu, Satoru; Iguchi, Yusuke*; Ono, Masao; Nishio, Taichiro*; Mashimo, Tsutomu
no journal, ,
A homogeneous Bi-Pb alloy was treated under mega-gravity field. Sedimentation and associated crystallization occurred during the process. The compositional graded superconducting alloy is obtained. The superconductivity parallel to gravity is Pb, and perpendicular to gravity is BiPb.
Okayasu, Satoru; Ono, Masao; Nishio, Taichiro*; Nakai, Noriyuki; Hayashi, Nobuhiko*; Machida, Masahiko; Iguchi, Yusuke*; Mashimo, Tsutomu*
no journal, ,
In high gravitational fields up to one million G, sedimentation of cecompositional atoms may occur even in solid. An In-Pb alloy sample (In:Pb=8:2) was prepared under a mega-gravity (1.02 MG) circumstance at 125C for 100 hours. After the maga-gravity treatment, an atomic scaled compositionally graded structure is formed in entire sample. A sample with continuously varying superconducting transition temperatures Tc is obtained. The effect of the varying Tc on vortices is investigated using a scanning SQUID microscope.
Okayasu, Satoru; Nishio, Taichiro*; Ono, Masao; Nakai, Noriyuki; Hayashi, Nobuhiko*; Machida, Masahiko; Iguchi, Yusuke*; Mashimo, Tsutomu
no journal, ,
Sedimentations of compositional atoms in solid can occur in a nonequilibrium diffusion under extremely strong centrifugal acceleration field (mega gravity). Under the mega gravity field, heavy atoms move along the field direction. Once the field is released, the composition of the atoms are fixed. Thus, the compositionally graded materials can be generated. In a Indium-lead alloy, an example of a complete solid solution, a spatially graded material can be formed in entire sample. This means that material parameter can be controlled in atomic level. In the InPb case, the local supeconducting transition temperatures of the sample change continuously. The superconducting properties of the sample will be discussed.
Nishio, Taichiro*; Hirai, Yuya*; Shimizu, Hideki*; Ono, Masao; Okayasu, Satoru; Ogata, Yudai*; Mashimo, Tsutomu*
no journal, ,
One of the ultimate goals in superconducting studies is the synthesis of a material which becomes superconducting at room temperature. However, the goal has not been in sight yet for more than 25 years after discovering a series of high-Tc copper-oxide superconductors. We think that behaviors of superconductors under extreme conditions give us a hint to obtain a higher transition temperature Tc. It is well known the Tc becomes higher under high pressure for most superconductors. The structual strain plays an important role for Tc. We forcus our attention to other structual strain caused by a mega-gravity. Under the mega-gravity, the heavier atoms move to the gravitational direction, and the lighter to the opposite. As a result, a different kind of strain can be applied. We show the changes of superconducting properties due to the maga-gravity for some superconductors.