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Dive into the research topics where Anming Hu is active.

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Featured researches published by Anming Hu.


Applied Physics Letters | 2001

Growth of single-domain (Sm0.5Eu0.5)Ba2Cu3O7−δ with high Tc and Jc by employing a thermal gradient

Anming Hu; N. Sakai; Masato Murakami

Bulk (Sm0.5Eu0.5)Ba2Cu3O7−δ superconductors were grown isothermally and with a vertical thermal gradient of −5 °C/cm in air. The crystals grown at a large growth rate under the thermal gradient exhibited a high-Tc value of 95 K and a plateau in the Jc–B curve at 1–4 T at 77 K with postannealing in Ar. We found that the substitution of Ba by rare-earth (RE) elements could be suppressed with a large growth rate. The narrow range of RE–Ba solid solution was attributed to the fast crystallization rate of RE1+xBa2−xCu3O7−δ with low-x values.


Applied Physics Letters | 1999

Enhanced flux pinning in (Nd0.33Sm0.67)Ba2Cu3O7−δ melt-processed superconductors by Ar postannealing

Anming Hu; P. Schätzle; W. Bieger; P. Verges; G. Fuchs; G. Krabbes

High-quality binary (Nd0.33Sm0.67)Ba2Cu3O7−δ monodomain superconductors were fabricated by the combination of a compositional-controlled melt-processing technique in air and postannealing in Ar. Critical current densities over the whole field range were observed strongly dependent on Ar postannealing while holding superconducting transition temperatures as high as 96 K. The suppressed chemical variation between the rare-earth element (RE: Nd, Sm) and Ba associated with disperse RE2BaCuOy (RE211) precipitate due to the decomposition occurring in Ar postannealing was attributed to the modified flux pinning. This makes Ar postannealing promising to process superconductors with desired properties for various applications.


Applied Physics Letters | 2005

Nanoscopic netted structure of compositional modulation in (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ superconductors

Anming Hu; Izumi Hirabayashi; M. Winter; Michael R. Koblischka; U. Hartmann; Hao Zhou

We report a nanoscaled crisscross network in high-quality melt-processed (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ superconductors investigated with atomic force microscopy (AFM) and transmission electron microscopy. In the ten-micrometer scale, such a net was unveiled as a consequence of crossing annular stripes originating from ordering compositional modulation. The AFM topographic images further displayed that this compositional stripe result in a surface modulation with a few-nanometer wavelength and roughness. The forming mechanism of this compositional stripe and its role as strong δTc-type pinning defects were discussed in the context of rare earth∕Ba oscillation around the stoichiometric ratio and the spatial fluctuation of local Tc values.


Superconductor Science and Technology | 1999

Melt processing and high performance of binary (Nd, Sm)-Ba-Cu-O superconductors

Anming Hu; P. Schätzle; W. Bieger; Peter Verges; G. Fuchs; G. Krabbes

Binary (Nd, Sm)-Ba-Cu-O superconductors with Tc of 96 K and a high irreversibility field up to 8 T have been fabricated in air via a newly developed technique. The initial composition was controlled by using binary (Nd, Sm)2BaO4 as an addition. In comparison with both NdBaCuO and YBaCuO melt-textured superconductors, the present composition showed a remarkable enhancement of critical current densities in an intermediate field regime (1-3 T). Microstructural observations and compositional analysis showed that the distributions of Nd and Sm in the (Nd, Sm)-123 matrix were homogeneous while the atomic ratio between these two rare earth elements was inconsistent with that in the nominal composition. These new characteristics were thought to cohere with the different solubilities between Nd and Sm in the liquid phase. Finally, trapped magnetic field mapping showed a single-domain shape of the trapped field, which indicated the growth of a single grain in the samples.


Superconductor Science and Technology | 2005

Effect of BaO2 and fine Gd2BaCuO7−δ addition on the superconducting properties of air-processed GdBa2Cu3O7−δ

Caixuan Xu; Anming Hu; N. Sakai; Mitsuru Izumi; Izumi Hirabayashi

Single-domain GdBa2Cu3O7−δ (Gd123) bulk superconductors were fabricated in air and studied with different BaO2 contents and Gd2BaCuO7−δ (Gd211) initial particle sizes. The experiments showed that BaO2 addition effectively suppressed the Gd/Ba substitution and therefore enhanced superconducting properties such as Jc and Birr. An optimum addition amount is Gd123:BaO2 = 1:0.1 molar. By employing fine Gd211, Jc at low magnetic fields is further enhanced. At B = 0 and 77 K, Jc reached 86 000 A cm−2, which is a record high Jc value for melt-processed Gd123 bulk samples in air.


Applied Physics Letters | 2003

Ordering oscillation of local composition in melt-processed REBa2Cu3O7−δ superconductors (RE: Sm, Eu, Gd)

Anming Hu; Masato Murakami; H. Zhou

High quality melt-processed GdBa2Cu3O7−δ, (Sm0.5Eu0.5)Ba2Cu3O7−δ and (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ single domains were grown in air and the microstructural origin of their distinguished superconducting performance was investigated by a transmission electron microscope equipped with energy-dispersive spectroscopy. A periodic array of the chemical composition with tens of micrometer correlation was unveiled due to the spatial oscillation of RE (RE: Sm, Eu, and Gd) and Ba around the stoichiometric ratio with a nanometer scale wavelength. For (Sm0.5Eu0.5)Ba2Cu3O7−δ, the temperature dependence of the reversible magnetic moment at certain fields showed two kinks. The first transition followed three-dimensional scaling and yielded dBc2/dT=1.98 T/K, corresponding to thermal fluctuation of the bulk superconductivity while the second displayed a linear temperature function with slightly lower Tc than bulk Tc and a slope of 0.6 T/K. This may indicate a field-induced pinning scenario with low Tc stripes.


Applied Physics Letters | 2002

Modulation of the peak effect in melt-processed (Sm1−xEux)Ba2Cu3O7−δ superconductors with compositional fluctuation

Anming Hu; H. Zhou; N. Sakai; Masato Murakami

The peak effect in melt-processed (Sm1−xEux)Ba2Cu3O7−δ crystals was modified with varying initial Sm/Eu ratios and was investigated up to 9 T down to 4.2 K. The experiment unveiled a linearly-temperature-dependent magnetization peak Bp(T). The fitting yielded a slightly lower critical temperature than bulk transition temperature Tc at null field. The scaling analysis of normalized pinning force versus reduced field B/Birr, where Birr is the irreversible field, showed a low peak at 0.37 in (Sm0.75Eu0.25)Ba2Cu3O7−δ and at 0.5 in (Sm0.25Eu0.75)Ba2Cu3O7−δ. The presence of regular compositional modulation is evident in both cases with transmission electron microscopy, and fluctuation diminishes in the latter composition. The modulation of flux pinning was thus attributed to the controlled compositional fluctuation.


Superconductor Science and Technology | 2005

Effect of Gd2Ba4CuMoOy addition on the band structure and spatial variation of superconducting properties in GdBa2Cu3O7−δ single domains

Caixuan Xu; Anming Hu; N. Sakai; Mitsuru Izumi; Izumi Hirabayashi

Gd2Ba4CuMoOy (Gd2411) single phase was synthesized in air and added into GdBa2Cu3O7−δ (Gd123) bulk superconductors with the addition amount ranging from 0.2% to 20%, in molar ratio to Gd123. Both microstructure and superconducting properties of each bulk were investigated from the seed position to the boundary of a single domain. Although a band structure with the alternative distribution of Gd2BaCuO5 (Gd211) and Gd2411 appeared in all samples, the range of this inhomogeneity only appeared within 5 mm from each side of the seed. The critical current density (Jc) shows that Gd2411 plays an important role in the control of the local superconducting properties. The highest Jc reached 84 500 A cm−2 at 77 K under the self-field in the sample with 0.4% addition of Gd2411.


Applied Physics Letters | 2006

Enhanced flux pinning of air-processed GdBa2Cu3O7−δ superconductors with addition of ZrO2 nanoparticles

Anming Hu; Caixuan Xu; Mitsuru Izumi; Izumi Hirabayashi; Masaki Ichihara

The authors investigate the influence of ZrO2 nanoparticles on microstructure and superconducting properties of GdBa2Cu3O7−δ (Gd123) single domain superconductors grown in air. Experiments show that before Gd123 crystallization ZrO2 nanoparticles react with Gd123 and yield BaZrO3. Transmission electron microscopy evidences that BaZrO3 disperses in Gd123 crystals with a size less than 50nm. A high Jc value of 100000A∕cm2 has been achieved in Gd123 with 0.4M% ZrO2 at 77K and self-field. Compared to the flux pinning effect of submicrometer Gd2BaCuO5 particles, BaZrO3 nanoparticles embedded in Gd123 significantly enhance critical current densities in a wide magnetic field range.


Physica C-superconductivity and Its Applications | 2002

Microstructures and superconducting properties of single domain (Sm0.5,Eu0.5)Ba2Cu3O7−δ superconductors fabricated in air

Anming Hu; N. Sakai; Kei Ogasawara; Masato Murakami

Abstract Single-domain (Sm 0.5 ,Eu 0.5 )Ba 2 Cu 3 O 7− δ grains were obtained via modified melt processing in air using NdBa 2 Cu 3 O 7− δ seeds. The facet growth front was observed in the a/b growth direction and the stepwise growth front in the c growth direction. A series of crystal defects: dislocations, twin boundaries and local chemical variations between rare earth and Ba were revealed by transmission electron microscopy and energy dispersive spectrum analysis. In addition, a slightly higher concentration of Sm than Eu was revealed in the matrix. A high T c value up to 94.5 K and enhanced J c values over a wide field range at 77 K were obtained after Ar post-annealing. A pellet of diameter 16 mm trapped 0.45 T field at 77 K.

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N. Sakai

Shibaura Institute of Technology

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Masato Murakami

Shibaura Institute of Technology

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Caixuan Xu

Tokyo University of Marine Science and Technology

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Mitsuru Izumi

Tokyo University of Marine Science and Technology

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H. Zhou

National Institute for Materials Science

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K. Inoue

Shibaura Institute of Technology

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