共查询到17条相似文献,搜索用时 62 毫秒
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测量了 2H Nb0 .9Ta0 .1 Se2 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 .同时在临界电流峰效应区的起始处出现一小峰 .实验结果表明掺Ta后 ,涡旋体系的动力学特性发生了显著的变化 . 相似文献
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通过改变磁场与c轴方向夹角测量了熔融织构YBa2Cu3O7-δ (YBCO)晶体的磁力矩信号响应, 观察到了磁通涡旋系统的锁定(lock-in)转变行为以及锁定转变角正比于外磁场强度的反常现象. 基于Ginzburg-Landau理论和磁通涡旋线Kink结构模型, 对上述锁定转变反常现象进行了分析讨论, 提出了熔融织构YBCO晶体中存在平行于a-b面的延展性关联缺陷结构假设, 导出了锁定转变临界角与温度和磁场之间的关系, 理论分析模型结果与实验测量结果基本符合. 相似文献
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在较宽的温度(4.2-80K)和磁场(0-8T)范围内测量了YBa2Cu3O7-δ和Y0.9Eu0.1Ba2·Cu3O7-δ样品的磁滞回线和磁弛豫,研究了其M(t),Jc(T)和Ueff(J)关系,并与现有的一些理论模型所预言的结果进行了比较。结果表明:(1)与YBa2Cu3O7-δ相比,Y0.9Eu0.1·Ba2Cu3O7-δ样品的有效钉扎势和无磁通蠕动时的临界电流密度有明显提高,表明Eu的部分替代引入了新的、具有更大的钉扎势的钉扎中心;(2)与其它模型相比,集体钉扎——蠕动理论对我们的实验结果作了更好的描述,因而本文为这一理论提供了新的实验证据。
关键词: 相似文献
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用直流磁控溅射法在(100)LaAlO3衬底上制备了La0.9Sr0.1MnO3薄膜.经退火处理后薄膜的原子力显微镜形貌观测和X射线衍射分析显示具有比较好的质量.电阻率-温度关系表明La0.9Sr0.1MnO3薄膜在281 K处发生金属绝缘体转变.电流在0.01—4 mA范围内,薄膜的峰值电阻率随电流增大而减小,在4 mA下获得了30.5%的峰值电阻率变
关键词:
掺杂锰氧化合物
0.9Sr0.1MnO3薄膜')" href="#">La0.9Sr0.1MnO3薄膜
电流诱导效应
相分离理论 相似文献
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高温超导体的发现动摇了支配磁通动力学二十几年的Kim-Anderson模型.于是人们提出了新的涡旋玻璃态模型,集体钉扎模型和U~j对数关系模型来描述高温超导体的磁通动力学.其中,涡旋玻璃态模型已被人们广泛接受.Fe基超导体发现后,人们它行为十分类似于高温超导体.我们实验上仔细研究了FeSe0.5Te0.5单晶的V~I关系曲线,发现上述诸模型均不能很好的解释我们的实验结果,而张的反跳模型恰能很好的拟合实验结果.本文讨论了诸模型对高温超导体磁通动力学描述的适用性并给出合理的解释. 相似文献
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通过制备(YBa2Cu3O7)1-x(V2O5)x(0≤x≤0.15)复合材料,获得了一系列典型的弱连接的颗粒超导体,其中以dR/dT-T关系中呈现出双峰转变为主要特征。第一峰代表晶粒的超导转变,第二峰代表颗粒系统超导长程序的形成。对于具有双峰转变的样品,其临界电流密度一致地符合ic~(1-t)n,n=1.6.这一行为与三维Josephson结网络系统的渗流行为相一致;对于不具有双峰转变的系统,临界电流密度随温度的变化尽管也可以用jc~(1-t)n描述,但是幂指数n明显地大于1.6,且随样品的不同而离散地分布。本文还对产生这种离散的原因进行探索和分析。
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Pr部分替代Ca可以在Bi-2223的超导层中引起局域缺陷(简称Pr离子缺陷),本文分析了不同含Pr量的Bi-2223/Ag带材在垂直于带面的外场下电阻转变特性,研究了其磁通钉扎势垒的变化规律.结果表明:Pr离子缺陷显著提高了Bi-2223带材的磁通钉扎势垒(U).不同含Pr量样品的磁通钉扎势垒(U)均满足U/(1-T irr/Tc0)(1/Hα的规律,其不同α值反映了样品中不同的磁通蠕动方式.在不含Pr离子缺陷的样品中,磁通主要以双弯结的方式进行蠕动, 含Pr离子缺陷的样品中磁通蠕动主要以直接剪切的方式进行. 相似文献
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Bismuth selenotelluride (Bi2(Te0.9Se0.1)3) films were electrodeposited at constant current density from acidic aqueous solutions with Arabic gum in order to produce thin films for miniaturized thermoelectric devices. X-ray fluorescence spectroscopy determined film compositions. X-ray diffraction pattern shows that the films as deposited are polycrystalline, isostructural to Bi2Te3 and covered by crystallites. Mueller-matrix analysis reveals that the electroplated layers are optically like an isotropic medium. Their pseudo-dielectric functions were determined using mid-infrared spectroscopic ellipsometry. Tauc-Lorentz combined with Drude dispersion relations were successfully used. The energy band gap Eg was found to be about 0.15 eV. Moreover, the fundamental absorption edge was described by an indirect optical band-to-band transition. From Seebeck coefficient measurement, films exhibit n-type charge carrier and the value of thermoelectric power is about −40 μV/K. 相似文献
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K.S. LeeJ.H. Yoo 《Current Applied Physics》2012,12(3):798-802
In the study, in order to develop the lead-free piezoelectric ceramics for actuator, transformer and other electronic-devices application, (K0.5Na0.5)(Nb0.9+xTa0.1)O3 + 0.5 mol% CuO + 0.2 mol% MnO2 ceramics were prepared by conventional mixed oxide method. The effects of B-site non-stoichiometry in [(K0.5Na0.5)] [(Nb0.9+xTa0.1)O3] ceramics on microstructure and piezoelectric properties were investigated. The density, electromechanical coupling factor (kp), mechanical quality factor (Qm), piezoelectric constant (d33), TC and TO-T of NKNT ceramics with x = 0.0065 showed the optimum values of 4.58 g/cm3, 0.427, 1554, 109 pC/N, 373 °C and 226 °C, respectively, suitable for piezoelectric motor, and transformer applications. 相似文献
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Brajendra Singh Ranjan K. Sahu S. Sundar Manoharan K. Drr K. -H. Müller 《Journal of magnetism and magnetic materials》2004,270(3):358-363
The substitutional effect of Ru on the magnetic and transport properties of double exchange ferromagnets, La0.7Sr0.3MnO3 and La0.5Sr0.5CoO3 has been investigated. It is found that substitution of 10% Ru at the Mn site of La0.7Sr0.3MnO3 decreases the Curie temperature by 20 K than that of the parent compound. However, a large decrease in the Curie temperature, ΔTc80 K and the system undergoes a transition from metallic state to insulating state is observed when 10% Ru is doped in La0.5Sr0.5CoO3. The marginal effect of Ru in the Mn–O–Mn sublattice in comparison to the Co–O–Co sublattice could be due to the magnetic exchange interaction between Mn and Ru by virtue of the fact that Ru exhibits variable valence states, Ru+4/Ru+5. The eg and t2g parentage of Ru+5 is similar to Mn+4 and therefore, Ru+5 ion appears to participate in the double exchange mediated ferromagnetic (FM) interaction. On the other hand, Ruthenium (IV) ion disrupts an intermediate spin state of cobalt (Co+3: t2g5eg1), forcing a double exchange FM state to anti-FM state. 相似文献
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Hrudananda Jena Santanu Bera K.V. Govindan Kutty T.R.N. Kutty 《Applied Surface Science》2008,254(21):7074-7079
X-ray photoelectron spectroscopic (XPS) studies were carried out on wet-chemically synthesized cubic BaTiO3, Ba0.9Nd0.1TiO3 and BaTi0.9Fe0.1O3−δ powders. The compounds were prepared by hydrothermal and gel to crystallite conversion technique; and phases formed readily at 420 K. The phase purity of the powders was confirmed from X-ray diffractometry. Chemical state and chemical environment of the constituent elements in the compositions were examined by XPS. Ba2+ was found to exist in two different chemical environments in these titanates. The Ti 2p3/2 photoelectron peak in BaTi0.9Fe0.1O3−δ was found to be broadened after Fe3+ substitution. Any resolvable broadening was not observed distinctly in the Ti 2p peak for Ba0.9Nd0.1TiO3, unsintered BaTiO3 and BaTiO3 annealed in hydrogen (8% H2 + Ar) at 1000 K. The prevalence of mixed-valent titanium and iron in BaTi0.9Fe0.1O3−δ composition was evident from the XPS results and was further supported by the enhanced electrical conductivity at 298-550 K for BaTi0.9Fe0.1O3−δ in comparison to BaTiO3 and Ba0.9Nd0.1TiO3. Hydroxyl incorporation was facilitated by substituting Nd3+ in Ba-sublattice. The presence of hydroxyls was observed from the broadening of the O 1s peak in XPS studies of the compounds. 相似文献