Sr_2RuO_4正常态的c方向的磁阻的研究

研究了典型的层状钙钛矿结构超导单晶Sr2RuO4在c方向的磁阻(Δρ/ρ0)(H∥ab,J∥c)的变化.实验发现,磁阻表现出强烈的各向异性,并且随着温度T的降低,磁阻效应越明显;当在平面ab内旋转磁场H的方向时,磁阻成周期性变化;实验表明,磁场沿(110)方向时,出现磁阻的极大值.分别从Sr2RuO4的费米面的各向异性、载流子散射率、c方向能带色散的各向异性等方面来解释这些输运性质.     

Sr2RuO4正常态的c方向的磁阻的研究

研究了典型的层状钙钛矿结构超导单晶Sr₂RuO₄在c方向的磁阻(Δρ/ρ₀)(H∥ab,J∥c)的变化.实验发现,磁阻表现出强烈的各向异性,并且随着温度T的降低,磁阻效应越明显;当在平面ab内旋转磁场H的方向时,磁阻成周期性变化;实验表明,磁场沿(110)方向时,出现磁阻的极大值.分别从Sr₂RuO₄的费米面的各向异性、载流子散射率、c方向能带色散的各向异性等方面来解释这些输运性质. 关键词： 2RuO₄')" href="#">Sr₂RuO₄ 磁阻     

Sr2RuO4的热电势

Sr2RuO4是第一个无CuO面的层状强关联氧化物超导体.测量了9至260K温度范围内Sr2RuO4的热电势,观测到在此温度范围内其热电势为正值.用两种载流子模型对实验数据进行了拟合,并且与Hall系数的实验结果进行了比较,发现低温下两种载流子对热电势和Hall系数的贡献比较类似,但在高温区空穴对热电势的贡献很大而相应地对Hall系数的贡献不占主要地位. 关键词： Sr2RuO4 热电势     

Magnetic and Electrical Transport Properties of Sr1-xLaxRuO3 (0≤x≤0.10)

We investigate the lightly doped polycrystalline Sr1-χLaχRuO3 （χ = 0, 0.02, 0.08 and 0.10）. With La doping, the ferromagnetism in the system has been suppressed. The transition temperature is T＇c at which the long-range ferromagnetism establishes and the magnetization under 3 T at 5 K decreases with increasing χ. In contrast to Sr1-χCaχRuO3, the samples remain with the PM-FM transition at 162K, which might be attributed to the valency change of Ru.     

苯并18-冠-6配合物[K(B18-C-6)]SCN的合成与结构分析

苯并 18 -冠 - 6 (B18- C- 6 )与 K2 [Cd(SCN) 4 ]反应 ,得到了 [K(B18- C- 6 ) ]SCN配合物。通过元素分析、红外光谱、单晶 X射线衍射进行了结构分析。该配合物为单斜晶系 ,空间群 P2 (1) / c,晶体学数据 :a=0 .996 0(3) nm,b=2 .5 0 97(7) nm,c=0 .8374 (2 ) nm,β=10 6 .5 19(5 )°,V=2 .0 0 6 7(10 ) nm3 ,Z=4 ,F(0 0 0 ) =86 4,R1=0 .0 4 2 9,w R2 =0 .0 5 75。结构分析表明 ,该配合物由一个 [K(B18- C- 6 ) ]配阳离子和一个 SCN阴离子组成 ,配合物的两个分子通过 K+ - π相互作用形成一维链状结构     

La2-xSrxCuO4单晶的平面内磁阻研究

测量了三种不同组分La2-xSrxCuO4(x＝0.09,0.18,0.24)单晶的平面内横向(H∥c,J∥ab)和纵向(H∥J∥ab)磁阻,发现平面横向与纵向磁阻都是正的,并且纵向磁阻与横向磁阻相比较很小,表明横向磁阻的主要贡献是电子轨道部分,也反映了ab面内和c方向电子有效质量的各向异性.三种成分单晶样品的平面内横向磁阻在不同温度随Sr含量x的变化显示在最佳掺杂浓度附近平面横向磁阻最大.     

{[K(18-C-6)][K(H_2O)_2]}[Cd(CN)_4]的合成与结构分析

合成了配合物 { [K(18- C- 6 ) ][K(H2 O) 2 ]} [Cd(CN) 4 ](1) ,并通过元素分析、红外光谱、单晶 X-射线衍射进行了结构分析。配合物属单斜晶系 ,空间群 P2 (1) / n。晶体学数据 :a=0 .936 5 3(18) nm,b=1.6 178(3) nm,c=1.74 81(3) nm,β=91.332 (3)°,V=2 .6 479(9) nm3 ,Z=4 ,Dcalcd=1.4 5 3g/ cm3 ,F(0 0 0 ) =12 0 8,R1=0 .0 317,w R2 =0 .0 5 6 7。配合物中 [K(18- C- 6 ) ],[K(H2 O) 2 ]和 [Cd(CN) 4 ]基团通过 K N键和 K —π相互作用形成三维网状结构     

Bi_2Sr_2CaCu_2O_8的晶体结构与超导性能

本文研究了Bi-Sr-Ca-Cu-O体系中理想成份为Bi_2Sr_2CaCu_2O_8化合物的超导性能和晶体结构。名义成份为BiSrCaCu_2O_(5.5)零电阻超导转变温度T_c(0)=81.5K。用X射线粉末衍射方法测定了Bi_2Sr_2CaCu_2O_8的晶体结构,其基本结构属体心四方晶系,空间群为D_(4h)~(17)-l4/mmm,点阵常数a=3.825A,c=30.82A。每单胞化合式单位为2.2Ca占据2(a)等效点系,4Sr,4Bi和4Cu占据三组4(e)位置,其原子参数z分别为0.110,0.302和0.445,16O分别占据8(g),z=0.445和二组4(e),z=0.210和0.380。Bi_2Sr_2CaCu_2O_8晶体结构可认为是阳离子沿z轴的(00z)和((1/2)(1/2)z)交错排列,由Aurivillius相导生出来的。讨论了在Bi-Sr-Ca-Cu-O体系中可能存在的其它沿z轴不同堆垛层数的超导相。     

{[K(18-C-6)][K(H2O)2]}[Cd(CN)4]的合成与结构分析

合成了配合物 { [K(18- C- 6 ) ][K(H2 O) 2 ]} [Cd(CN) 4 ](1) ,并通过元素分析、红外光谱、单晶 X-射线衍射进行了结构分析。配合物属单斜晶系 ,空间群 P2 (1) / n。晶体学数据 :a=0 .936 5 3(18) nm,b=1.6 178(3) nm,c=1.74 81(3) nm,β=91.332 (3)°,V=2 .6 479(9) nm3 ,Z=4 ,Dcalcd=1.4 5 3g/ cm3 ,F(0 0 0 ) =12 0 8,R1=0 .0 317,w R2 =0 .0 5 6 7。配合物中 [K(18- C- 6 ) ],[K(H2 O) 2 ]和 [Cd(CN) 4 ]基团通过 K N键和 K —π相互作用形成三维网状结构     

高温超导体Bi_(1.6)Pb_(0.4)Ca_2Sr_2Cu_3O_y中的表面超导相

在 Bi_(1.6)Pb_(0.4)Ca_2Sr_2Cu_3O_y 样品中存在着110K 和85K 两个超导相,样品的零电阻温度为105K.磁化率、比热以及不同温度下的 M-H 曲线测量结果均表明85K 相为表面超导相,在样品中占有较小的体积分数.文中还报道了样品的H_(c1)(0).     

Change in the sign of the magnetoresistance effect in bilayer superconductor/ferromagnet structures under change in the type of the domain structure in the ferromagnet

The magnetoresistance effects in the bi- and trilayer hybrid planar superconductor/ferromagnet (S/F) structures based on Py (permalloy) and Nb near the superconducting transition temperature T _C are considered. It has been experimentally shown that the sign of the observed magnetoresistance peaks in the bilayer S/F systems changes from negative to positive at the permalloy layer thickness corresponding to the change in the type of domain walls from Néel to Bloch. For the Néel walls at the ferromagnet coercive fields, the negative magnetoresistance effect, which is due to a decrease in the depairing action of the exchange field E _ex, is observed in the S/F bilayers. For the Bloch domain walls, the magnetoresistance of the bilayer S/F structures is determined by the dissipative motion of Abrikosov vortices in the superconducting layer. In the trilayer F/S/F structures, the magnetoresistance is mainly due to the suppression of the superconducting order parameter in the superconducting layer under the action of the accumulation of the spin-polarized carriers near the S/F interfaces.     

Superconducting gap anisotropy in Nd1.85Ce0.15CuO4: results from photoemission

We have performed angle resolved photoelectron spectroscopy on the electron doped cuprate superconductor Nd1.85Ce0.15CuO4. A comparison of the leading edge midpoints between the superconducting and normal states reveals a small, but finite shift of 1.5-2 meV near the ( pi,0) position, but no observable shift along the zone diagonal near ( pi/2, pi/2). This is interpreted as evidence for an anisotropic superconducting gap in the electron doped materials, which is consistent with the presence of d-wave superconducting order in this cuprate superconductor.     

对靶溅射技术制备的La2/3Ca1/3MnO3/YBa2Cu4O8/La2/3Ca1/3MnO3薄膜中Tc的降低

本文用对靶溅射技术制备了La2/3Ca1/3MnO3/YBa2Cu4O8/La2/3Ca1/3MnO3薄膜.与YBCO单层薄膜相比,由于超导/铁磁系统中的磁性邻近效应,三层薄膜表现出较低的超导转变温度.薄膜的R～T测量曲线显示出超磁阻(CMR)效应和超导转变,预示着超导和铁磁特性共存于LCMO/YBCO/LCMO三文治结构.     

Magnetoresistance of porous polycrystalline HTSC: Effect of the transport current on magnetic flux compression in intergranular medium

The hysteretic dependences of the magnetoresistance of porous (38% of the theoretical density) granular high-temperature superconductor (HTSC) Bi_1.8Pb_0.3Sr_1.9Ca₂Cu₃O _x have been analyzed in the model of the effective intergranular field. This effective field has been defined by the superposition of the external field and the field induced by magnetic moments of superconducting grains. The magnetic flux compression in an intergranular medium, characterized by the effective field, controls the hysteretic behavior of the magnetoresistance. It has been found that the magnetoresistance hysteresis width for the studied porous HTSC depends on the transport current, in contrast to the superconductor of the same composition with high physical density (more than 90% of the theoretical value). For a porous superconductor, a significant current concentration occurs in the region of the grain boundaries, which is caused by features of its microstructure. A current-induced increase in the effective boundary length results in a decrease in the flux compression, a decrease in the effective field in the intergranular medium, and a magnetoresistance hysteresis narrowing with increasing current.     

具有人工晶界的Sr2FeMoO6粉末磁电阻的温度特性

利用固相反应合成了纯相的Sr2FeMoO6多晶块体，并通过机械球磨方法引入了人工晶界，研究了具有此种晶界的Sr2FeMoO6粉末磁电阻的温度特性．X射线衍射分析表明，机械球磨过程没有改变Sr2FeMoO6的晶体结构，但却在晶粒间界处引入了SrMoO4绝缘相，其量随着球磨时间的增加而增加．不同磁场下的磁电阻测量结果表明，由于一定量SrMoO4绝缘相的存在，晶粒间的绝缘隧穿势垒得到加强，更有利于自旋极化电子在晶粒间的隧穿，从而提高了Sr2FeMoO6多晶粉末的低温磁电阻值．然而随着温度的升高，磁电阻值迅速下降，表现出较强的温度依赖关系．这种现象是由于随着温度的升高，电子在晶界局域态间的非弹性跳跃逐渐增强引起的，而晶界局域态是由在晶界附近的大量缺陷构成．分析表明，晶界状态对Sr2FeMoO6多晶粉末磁电阻的温度特性有十分重要的影响．     

Magnetic breakdown in the electron-doped cuprate superconductor Nd(2-x)Ce(x)CuO4: the reconstructed Fermi surface survives in the strongly overdoped regime

We report on semiclassical angle-dependent magnetoresistance oscillations and the Shubnikov-de Haas effect in the electron-overdoped cuprate superconductor Nd(2-x)CexCuO4. Our data provide convincing evidence for magnetic breakdown in the system. This shows that a reconstructed multiply connected Fermi surface persists, at least at strong magnetic fields, up to the highest doping level of the superconducting regime.     

Giant magnetoresistance in ferromagnet/superconductor superlattices

We show magnetoresistance in excess of 1000% in trilayers containing highly spin-polarized La0.7Ca0.3MnO3 and high-Tc superconducting YBa2Cu3O7. This large magnetoresistance is reminiscent of the giant magnetoresistance (GMR) in metallic superlattices but with much larger values, and originates at spin imbalance due to the injection of spin-polarized carriers. Furthermore, in contrast to ordinary GMR, the magnetoresistance is intimately related to the superconductivity in the YBa2Cu3O7 layer and vanishes in the normal state. This result, aside from its fundamental importance, may be of interest for the design of novel spintronic devices based on ferromagnet/superconductor structures.     

高温超导薄膜微波表面电阻测量标准理论精度修正

高温超导薄膜的表面电阻Rs作为应用超导器件设计和性能衡量的一个重要参数,对超导无源微波元件的设计和开发有很重要意义.准确测量超导薄膜的表面电阻Rs也就非常重要.国际通用的标准测量方案中的理论模型公式是基于高温超导膜无限大的基础上的.考虑到实际超导薄膜的总是有限大的情况,我们从理论上进行了精度分析,在此基础上对此理论模型公式进行了修正,求出基于超导膜有限大时的Rs的表达式,并对两种情况进行了一定的比较.     

Quantum Dynamical Approach to Various Scattering Mechanisms and Their Influences on Thermal Conductivity of Sr- and Zn-Doped La2CuO4 High-Temperature Superconductor Cuprate

JETP Letters - A theoretical investigation of the thermal conductivity of lightly Sr- and Zn-doped La2CuO4 high temperature superconductor cuprates has been analyzed auspiciously. We used a quantum...     

EuS/Ta异质结的极大磁电阻效应

在铁磁/超导异质结中,铁磁体的交换场通过近邻效应将导致超导体准粒子态密度的塞曼劈裂.基于该效应,在外磁场不强的情况下,通过外加磁场可以有效地调节铁磁/超导界面处的交换作用,从而实现超导体在正常态和超导态之间转换,产生极大磁电阻.本文利用脉冲激光沉积方法制备了EuS/Ta异质结并研究了其电磁特性.Ta在3.6 K以下为超导态,EuS在20 K以下为铁磁态.在2 K时,EuS/Ta异质结中可观测蝴蝶型磁滞回线,证明在低磁场下(<±0.18 T)异质结中EuS铁磁态和Ta超导态共存.磁输运测试表明,通过施加外磁场可以有效调节EuS的交换场,随着交换场的增大,同时也加强了界面处的交换作用,从而抑制Ta的超导态,实现了Ta在超导态和正常态之间的转变,在EuS/Ta异质结中观测到了高达144000%的磁电阻.本文制备的EuS/Ta异质结具有极大磁电阻效应,在自旋电子学器件中有潜在的应用前景.