检索结果-南通市图书馆

Grain Size Dependence of Exchange-Coupling Interaction between Magnetically Soft-Hard Grains and Effective Anisotropy

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2004年第6期22卷 790-793页

作者：韩广兵高汝伟傅爽刘汉强冯维存陈伟 School of Physics & Microelectronics Shandong University Jinan 250100 ChinaSchool of Physics & Microelectronics Shandong University Jinan 250100 ChinaSchool of Physics & Microelectronics Shandong University Jinan 250100 ChinaSchool of Physics & Microelectronics Shandong University Jinan 250100 ChinaSchool of Physics & Microelectronics Shandong University Jinan 250100 ChinaSchool of Physics & Microelectronics Shandong University Jinan 250100 China

Taking α-Fe and Nd_2Fe_(14)B grains as example, the grain size dependence of the exchange-coupling interaction and effective anisotropy and also their variations depending on the ratio of magnetically soft and hard grain sizes, D_s∶D_h, were investigated. When grain size D>L_(ex), the grain’s anisotropy is the statistic value of the coupled and uncoupled part. The anisotropy constant of uncoupled part is the common value K_1 and that of coupled part varies with the distance to the grain surface. The effective anisotropy constant between magnetically soft and hard grains, K_(eff), can be expressed as the sum of the products of volume fractions for soft and hard grains, respectively, and the corresponding mean anisotropy constants. The calculation results indicate that the exchange-coupling interaction is enhanced with the reduction of grain size, and the effective anisotropy decreases with reducing grain size and increasing ratio of D_s∶D_h. In order to get high effective anisotropy constant, K_(eff), in composite magnetically soft-hard grains, the hard grain size should be larger than 30 nm and the soft grain size should be about 10 nm.

关键词： metal materials exchange-coupling interaction effective anisotropy magnetic grains rare earths

Structure and Transport Properties of La_(0.67)Ca_(0.33)Mn_(1-x)Al_xO_3

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2004年第4期22卷 492-496页

作者：崔玉建贾广强韩雁冰王新燕葛洪良张金仓 Department of Applied Physics China Institute of Metrology Hangzhou 310018 China Department of Physics Shanghai University Shanghai 200436 China

The effects of Al ion doping on the Mn site were studied for the colossal magnetoresistance material La_(0.67)Ca_(0.33)MnO_3. It is found that the volume of the crystal cell decreases monotonically when the population of Al^(3+) increases across the entire doping range. As the Al^(3+) population increases, the resistance of the material rises rapidly, while the insulator-metal transition temperature T_(IM) decreases linearly. At small Al^(3+) dosage, a thermal activation model properly describes the transport properties at T>T_(IM), while a metallic model is more suitable at T

关键词： metal materials structure and transport properties Al^(3+) substitution La_(0.67)Ca_(0.33)MnO_3 rare earths

A Study on La_2O_3-Y_2O_3-Mo Secondary Emission Material

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2003年第6期21卷 633-636页

作者：王金淑刘娟周美玲李洪义张久兴左铁镛 Key Laboratory of Advanced Functional materials of Ministry of Education School of Materials Science and Engineering Beijing Polytechnic University

The substrate molybdenum doped with La_2O_3, Y_2O_3 cathode material was made by the powder metallurgy method. The secondary emission coefficients of the materials were tested. The experimental results show that Mo cathodes doped with La_2O_3,Y_2O_3 have good secondary emission properties. When the cathodes are activated, the maximal secondary emission coefficients of these cathodes are higher than 2.0 and can meet the practical requirement. The distribution of the rare earth in the interior and at surface of this kind of cathode material before and after emission was studied using Scanning Electronic Microscopic (SEM) and X-Ray Photoelectron Spectrum(XPS). The analysis results show that the rare earth is easy to gather at grain boundaries and the relevant concentration of rare earth on the surface after emission is obviously greater than that before emission.

关键词： metal materials secondary emission molybdenum cathode rare earths

Effects of Current-Injection on Superconductivity of YBa_2Cu_3O_(7-δ) in La_(0.8)Te_(0.2)MnO_3/YBa_2Cu_3O_(7-δ)Bilayer

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2005年第2期23卷 254-256页

作者：朱亚彬戴守愚 Department of Physics College of Science Beijing Jiaotong University Beijing 100044 China Laboratory of Optical Physics Institute of Physics and Center for Condensed Matter Physics Chinese Academy of Sciences Beijing 100080 China

La_(0.8)Te_(0.2)MnO_3/YBa_2Cu_3O_(7-δ)(F/S)bilayers were fabricated by electrophoretic technique. The thickness of La_(0.8)Te_(0.2)MnO_3 is ~70 μm, the dimensions of YBa_2Cu_3O_(7-δ) superconductor are 5 mm×10 mm×0.5 mm. The image of cross-sectional profile was measured by scanning electron microscopy (SEM). Standard four-probe method was used for YBa_2Cu_3O_(7-δ) superconducting resistance measurements. Either 1 mA current is injected from S layer to F layer ((+I_(inj))) or from F layer to S layer (-I_(inj)),the normal resistance is lower than that without current injection. The critical transition temperature is higher than that without current injection.

关键词： metal materials colossal magnetoresistance superconductivity injection-current rare earths

Effect of Yttrium on Microstructures and Properties at Elevated Temperature of Mg-0.8Zr-0.35Zn Alloys

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2004年第2期22卷 268-271页

作者：梁维中宁志良王海波刘洪德刘洪汇 School of metal materials Harbin University of Science and Technology Harbin 150040 China Harbin Dongan Autoengine Joint-Stock Co. Ltd Harbin 150056 China

The effects of Y addition on microstructures and properties of as-cast and solid solutioning and aging treated Mg-0.8Zr-0.35Zn alloys at elevated temperature (250 ℃) were investigated by the use of XJG-04 optical microscopy, JCXA-733 electron probe, D/max-rB X-ray diffractometer (XRD) and WDW-200 electronic universal material testing machine. The results show that the microstructures of as-cast and heat treated Mg-0.8Zr-0.35Zn alloys with Y addition are refined and a new phase, Mg_(24)Y_5, is formed. At 250 ℃, the strength at elevated temperature of the alloys increases with increasing amount of Y addition, but relative elongation and area reduction decreases. The tendency of brittle fracture of fractured surface at elevated temperature is enlarged and fracture is changed from ductile into cleavage.

关键词： metal materials microstructures elevated temperature properties rare earth metal

Hydrogen Absorption of Nd-Fe-B Alloys

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2004年第5期22卷 668-672页

作者：谭春林白书欣张虹张家春蔡珣 College of materials Science and Chemical Engineering Zhejiang University Hangzhou 310027 China ( School of materials Science and Engineering Shanghai Jiaotong University Shanghai 200030 China Department of materials Engineering and Applied Chemistry National University of Defense Technology Changsha 410073 China School of materials Science and Engineering Shanghai Jiaotong University Shanghai 200030 China . Department of materials Engineering and Applied Chemistry National University of Defense Technology Changsha 410073 China

The technical parameters of HD process were studied, including the effects of temperature and neodymium contents on the incubation period of hydrogen absorption, hydrogen concentration and the rate of hydrogen absorbed. The results show that the incubation period is shortened and the rate of hydrogen absorbed is accelerated with rising temperature and surface area. These are attributed to the rising rate of hydrogen diffusion at higher temperature. The change of the incubation period and the rate of hydrogen absorbed have the similar trend resulted from the increasing content of the Nd-rich phase owing to the rising temperature. Moreover, the percent of the Nd-rich phase in the ingot can be calculated according to the total hydrogen weight gain.

关键词： metal materials hydrogen decrepitation neodymium content surface area NdFeB rare earths

Evolution of Sm2Fel7 Alloys during Hydrogenation-Disproportion Process

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2005年第5期23卷 542-545页

作者：叶金文刘颖李梦高升吉涂铭旌 Department of metal materials Sichuan University Chengdu 610065 China

The evolution of phase compositions, phase change and microstructure in Sm2Fe17 alloys during hydrogenationdisproportion process were systematically studied with XRD, SEM, EDX methods. Research indicates that HD process of Sm2Fe17 alloys is as follows： Sm2Fe17 alloy absorbs hydrogen first in the atmosphere of hydrogenation with a pressure of 0.1 MPa. Disproportionation begins at T ≥ 500 ℃, then the alloys tuna into lots of SmHx and α-Fe phases which are partly in microcrystal or amorphous structures. Along with the increase of temperature, the microcrystal and amorphous structures transformed into crystal structure and this transformation thoroughly completed at 750 ℃. The size of obtained crystal grain is about 20 - 100 nm. Based on the experimental data, a microstructural transformation model of Sm2Fe17 alloys during hydrogenation-disproportion process was made.

关键词： metal materials HDDR hydrogenation nitride rare earths

Lithofacies Phases Analysis of Cover Flux in Tundish for Rare Earth Treated Steel

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2003年第S1期21卷 194-197页

作者：姜茂发姚永宽刘承军王德永 College of materials and metallurgy Institute Northeastern University

Lithofacies structure of commercial cover flux and experimental slags were analyzed,and states of rare earth oxides in cover flux were studied. The results show that under the experiment conditions,the mineral structures of original slags are mainly the calcium feldspar,a lot of magnesium olivine and Fe-bearing silicate. Rare earth oxides in the cover flux exist mainly as rare earth silicates. When the content of rare earth oxides reaches a certain value,rare earth oxides precipitate in molten cover flux. It means that the solubility of rare earth oxides is limited. Rare earth oxides may be partly substituted for CaO to form rare earth-silicate which may increase with the basicity reducing.

关键词： metal materials lithofacies rare earth oxides cover flux in tundish rare earths

Recrystallization Texture and Microstructure of metal Substrate for Y123 Coated Superconductor

在线全文

学校读者我要写书评

暂无评论

Journal of Rare Earths 2003年第4期21卷 450-452页

作者：刘慧舟史锴杨坚袁冠森 Superconductivity Research Center

The cube textured pure Ni and non magnetic Cu Ni tapes were obtained by rolling and recrystallization, and these tapes are suitable as substrates of the second generation high temperature superconducting tape. The texture of tapes was studied using Orientation Distribution Function (ODF) and φ scans. The results indicate that sharp cube texture of Cu 0 70 Ni 0.30 and pure Ni was formed at 1000 ℃ and that of Cu 0 85 Ni 0.15 was formed at 900 ℃. The intensities of cube texture differ from each other. Uniform equiaxial crystallites are formed in all the tapes and the size of Cu 0.85 Ni 0.15 is larger than that of Cu 0.70 Ni 0.30 and pure Ni. Annealing twin is formed in Cu 0.85 Ni 0.15 and Cu 0.70 Ni 0.30 .

关键词： metal materials high temperature superconductor cube texture substrate twin rare earths