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1.
测量了中子辐照熔融织构YBa_2Cu_3Oy样品从1.5 K到85K之间一系列温度下的磁化曲线。磁场H平行于c轴时,在6K观察到磁通跳跃。中子辐照可使临界电流提高一个数量级。分析了临界电流的各向异性,辐照增强与磁场的关系和主要的钉扎中心。讨论了磁通跳跃的物理模型。  相似文献   

2.
张波  田明亮  张裕恒 《物理学报》2001,50(11):2221-2225
测量了2H-Nb0.9Ta0.1Se2单晶样品在不同电流下电压随磁场变化的曲线V(H),并从V(H)曲线得到V(I)数据.使用标度关系V=α(I-Ic)β进行了拟合,得到了临界电流随磁场Ic(H)和微分电阻随磁场Rd的变化关系.在微分电阻随磁场变化的曲线中,电流较大时,靠近上临界磁场Hc2附近出现一个强峰,而在低电流下,该峰消失.同 关键词: 磁通涡旋 标度定律 临界电流峰效应  相似文献   

3.
测量了熔融织构YBCO样品从1.5K到89K的磁化曲线。磁场H平行于c轴时,在1.5K,7K和10K观察到磁通跳跃,在15—83K的温度区间观察到峰值现象。详细分析了磁化曲线和磁临界电流的各向异性。讨论了晶粒之间连接的性质和主要的钉扎中心。 关键词:  相似文献   

4.
高温超导材料在应用上的主要困难是临界电流密度太低.问题在于混合态时材料中磁通线所受的钉扎力较弱,稍大一点的电流通过会引起磁通线的运动,从而产生电阻破坏超导电性,早些时候,很多人认为这个缺点很难甚至不可能被克服. 1989年,中子辐照YBa-2Cu-3O-7样品对临界电流影响方面的实验给人们以希望.例如贝尔实验室 Bruce Van Dover 等人进行的辐照实验,辐照前,77K下YBa-2Cu-3O-7晶体最大的临界电流密度为6500A/ cm~2 ,辐照后,提高到620000A/cm~2.也许是辐照产生的小缺陷成为磁通线的钉扎中心. 临界电流密度提高100倍的结果只在一个晶…  相似文献   

5.
对c轴择优取向的熔融织构样品(Nd0.33Eu0.33Gd0.33) Ba2Cu3O7-δ(含Gd(211)相)的磁通跳跃现象进行 了系统研究.结果表明,在外加磁 场平行于样品c轴条件下,在2到3K的温度范围内明显观测到了部分磁通跳跃现象,而 在5K及以上温区并未出现.在磁场垂直于样品的c轴情况,在2K到Tc的整个温 区都没有观察到磁通跳跃现象.这种各向异性磁通跳跃现象可归因于各向异性钉扎力和几何 退磁因子的结果.随着温度的增加,磁通跳跃数目减少,且M(H)曲线的第三象限是磁通 跳跃的最不稳定过程.最后,研究了磁通跳跃对磁场扫描速率的依赖关系,并讨论了磁通蠕 动对磁通跳跃的影响. 关键词: 0.33Eu0.33Gd0.33)Ba2Cu3O7-δ超导体')" href="#">(Nd0.33Eu0.33Gd0.33)Ba2Cu3O7-δ超导体 OCMG方法 磁通跳跃  相似文献   

6.
董石泉  何安  刘伟  薛存 《物理学报》2023,(1):303-314
超导磁悬浮列车在加速启动的过程中,载有恒定大电流的超导线圈处在变化的磁场中,这会导致超导线圈发生磁通跳跃,从而降低线圈的载流能力.并且磁通跳跃会产生大量热量而使超导线圈温度急剧升高,严重时会导致超导线圈失超,所以对磁通跳跃的研究具有非常重要的科学意义.Nb3Sn超导线是由多根微米级的超导芯丝、铜和环氧树脂形成的复合结构.本文通过约束每根芯丝的静电流为零的二维模型来分析三维绞扭效应,研究了超导线在交变磁场和恒定电流下的磁热不稳定性行为.通过分析交变磁场的幅值和频率对Nb3Sn超导线磁通跳跃的影响,发现当磁场幅值不变时,初次发生磁通跳跃的磁场阈值Bth随频率非单调变化.而当频率一定时,初次发生磁通跳跃的磁场阈值Bth随交变磁场幅值单调变化.此外,随着幅值的减小,发生磁通跳跃的频率区间先变大后变小,直到某个临界频率后超导线不再发生磁通跳跃.本文的研究结果能够为调控超导线的磁热不稳定性行为提供理论依据.  相似文献   

7.
利用观察磁化随时间变化的方法研究了高Tc氧化物YBa2Cu3Oy超导体临界态的磁通蠕动。实验结果表明,零场冷却的样品,加一个所选定场值的磁场,产生的磁化随对数时间线性衰减,同时伴随有磁通跳跃的发生。磁化衰减速率dM/dlnt随外场H的变化在H=3HP附近有一峰值,并认为与弱连结超导电性的存在有关。在77K以上温度,dM/dlnt随温度的升高而单调减小。讨论了钉扎磁通的热激活能U0关键词:  相似文献   

8.
制备了银包套的Bi1.8Pb0.4Sr2Ca2.2Cu3Oy带材。微结构观察证明样品是高度织构化的Bi2223单相。输运测量发现Jc(T,B,θ,φ)和R(T,B,θ,φ)均与θ有关,与φ无关(T=77K,B<1T),式中的θ和φ分别表示磁场与ab面和电流的夹角。求得了磁通运动的激活能。提出了热激活磁通弯结的形成与运动模型,并用London理论计算了弯结 关键词:  相似文献   

9.
描述一种测量高温超导体磁通钉扎能U0及其分布的新方法,此方法主要之点是测量磁化后样品的零场临界电流随时间的变化,利用这一方法测量Tl2Ba2Ca2Cu3Oy的U0值分布(T=78K)。根据所得结果,对已报道的U0值的分散性提出一种新解释。 关键词:  相似文献   

10.
王春雷  易晓磊  姚超  张谦君  林鹤  张现平  王栋樑  马衍伟 《物理学报》2015,64(11):117401-117401
铁基超导体是在2008年由Hosono发现的一种新型超导材料, 由于其具有上临界场高、各向异性小、临界电流密度大等优点, 在世界范围内引起了广泛关注. 以Ba1-xKxFe2As2为代表的FeAs-122系超导体具有结构简单、合成温度低、单晶容易制备等优点, 是物理学家和材料学家关注的焦点. 本工作在获得最优化掺杂的Ba1-xKxFe2As2单晶(Tc = 38.5 K)基础上, 通过分析其在不同磁场条件下电阻温度变化关系、不同温度条件下的磁滞回线等数据, 系统的研究了Ba1-xKxFe2As2单晶磁通钉扎力和磁通钉扎机理. 研究发现Ba1-xKxFe2As2超导体具有非常高的磁通钉扎势, 其中9 T的外场条件下, 其在H//c轴和H//ab面的钉扎势分别为5800 K和8100 K, 展示出良好的应用前景; 通过进一步分析发现, 其磁通钉扎机理应是由于晶格内部的小尺寸缺陷引起的电子平均自由程变化而导致的δl钉扎.  相似文献   

11.
Incoherent inelastic neutron scattering has been used to study the motion of NH4+ ions in NH4+ β-alumina. The results establish that jump reorientation of NH4+ ions is rapid compared to translational diffusion: The data are consistent with thermally activated jumps between equivalent NH4+ orientations with a proton jump frequency of ~1.0 × 1012sec at room temperature.The data are inconsistent with either free rotation or unrestricted rotational diffusion. The residence time between translational diffusion jumps is >6 × 10?11 sec at temperatures less than 473°K.  相似文献   

12.
Here we report the magnetic and heat capacity studies of the double perovskite compounds Ba2SmRuO6 and Ba2DyRuO6. Antiferromagnetic transitions are inferred at 54 and 47 K in Ba2SmRuO6 and Ba2DyRuO6, respectively, in the magnetization measurements. Heat capacity measurements show large jumps at the corresponding temperatures and confirm the bulk magnetic ordering. Both the measurements provide clear indication of the ordering of the rare earth moments also along with the Ruthenium moments. However, the heat capacity results suggest that the ordering of rare earth magnetic moments is spread over a large temperature range. An anomaly observed in the magnetization measurements at 42 K (below the magnetic ordering) in Ba2SmRuO6 is discerned as a reorientation of Sm3+ moments.  相似文献   

13.
We have measured the second moment, the linewidth and the relaxation times T1 and T2 of the 1H magnetic resonance signal from 4.2 to 380 K in the fact proton conductors H2Sb4O11·nH2O. Our results reveal that the high ionic conductivity of these materials is due to a Grotthuss-type proton diffusion mechanism with succession of molecular reorientations of H3O+ ions or H2O molecules and of proton jumps from H3O+ to H2O.  相似文献   

14.
We present herein a comparison of the magnetic properties of bulk ceramics and thin films of the ferrimagnetic ErCo0.50Mn0.50O3 compound. Epitaxial thin films were deposited onto (1 0 0) SrTiO3 substrates by pulsed-laser ablation while bulk ceramics were prepared by solid state reaction. When cooling under low applied fields, a spin reversal is observed in both thin film and bulk due to the competition between two magnetic sublattices (Co/Mn and Er) coupled by a negative exchange interaction. Original features are observed in the M(H) loops for bulk materials: abrupt jumps at 4 T due to a reorientation of domains, while in the low field region, the increasing and decreasing branches of the magnetization intersect each other. In the thin film, the ordering temperature increased from 69 to 75 K, and the ZFC anomaly (AF transition) became sharper, compared to the bulk specimen. The oxygen content and the microstructure are crucial to observe the intersection of the magnetization branches.  相似文献   

15.
Polarization-optical studies and measurements of the birefringence Δn and the angle of rotation of the optical indicatrix for the (NH4)2NbOF5 crystal have been carried out in the temperature range 100–350 K. Two anomalies of the birefringence have been revealed at the temperatures T 01 = 258 K and T 02 ≈ 219 K. According to the twinning pattern, the crystal undergoes successive changes in symmetry: orthorhombic ↔ monoclinic 1 ↔ monoclinic 2. The twofold axis of the monoclinic phases (or the normal to the plane) is directed along [001]or. The effect of the uniaxial compression along [011]or and the electric field E ≈ 25 kV/cm along [100]or on the twin structure has been studied. The ferroelastic phase transition at T 01 is due to the appearance of the shear deformation x 4(T) and is accompanied by significant anomalies of the birefringence. Strong pretransition phenomena mask the jumps in the birefringence Δn(T) and in the angle of rotation of the indicatrix φ(T) at T 01.  相似文献   

16.
Complex magnetic, magnetoelectric and magnetoelastic studies of spontaneous and field-induced phase transitions in TmMn2O5 were carried out. In the vicinity of spontaneous phase transition temperatures (35 and 25 K) the magnetoelectric and magnetoelastic dependences demonstrated the jumps of polarization and magnetostriction induced by the field ∼150 kOe. These anomalies can be attributed to the influence of magnetic field on the conditions of incommensurate-commensurate phase transition at 35 K and the reverse one at 25 K. In b-axis dependences the magnetic field-induced spin-reorientation phase transition was also observed below 20 K. Finally the magnetoelectric anomaly associated with metamagnetic transition is observed below the temperature of rare-earth subsystem ordering at relatively small critical fields of 5 kOe. This variety of spontaneous and induced phase transitions in RMn2O5 stems from the interplay of three magnetic subsystems: Mn3+, Mn4+, R3+. The comparison with YMn2O5 highlights the role of rare earth in low-temperature region (metamagnetic and spin-reorientation phase transitions), while the phase transition at higher temperatures between incommensurate and commensurate phases should be ascribed to the different temperature dependences of Mn3+ and Mn4+ ions. The strong correlation of magnetoelastic and magnetoelectric properties observed in the whole class of RMn2O5 highlights their multiferroic nature.  相似文献   

17.
The a.c. magnetic susceptibility (χ) was measured for (C6H5CH2NH3)2CuCl4 (φC1Cl) above 4.2K, and two-consecutively anomalous behaviours of χ were observed at 6K and 6.9K. Brief discussions about these phenomena were given in relation to the two-dimensionality of φC1Cl system.  相似文献   

18.
The magnetic susceptibility of the layered compounds (CH2)3(NH3)2FeCl2Br2 and (CH2)6(NH3)2FeCl2Br2 has been measured in the range 80 < T < 300 K. The results follow a Curie-Weiss behavior in the range 120 < T < 300 K but are field dependent for T < 120 K. The results are interpreted in terms of a two-dimensional antiferromagnetic interaction which is canted. A comparison with the corresponding pure chloride compounds is given.  相似文献   

19.
测量了块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5在退火前后其电阻值随温度的变化,测量的温度范围为1.5—300K.样品在退火前后都发现有超导现象.零磁场下其超导转变温度Tc分别为1.84和3.76K.在5—300K温度范围内,原始样品具有负的电阻温度系数.如果取Zr, Ti, Cu, Ni及Be分别贡献出1.5, 1.5, 0.5, 0.5及两个传导 关键词: 块体金属玻璃 超导 电阻温度系数  相似文献   

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