铁磁复合对Bi2212相超导电性的抑制

我们成功制备了由高温超导Bi2212相和铁磁LCMO相两相复合的系列陶瓷样品.复合陶瓷样品的相分析表明无杂相生成,电阻温度曲线显示出铁磁性LCMO相对Bi2212相超导电性有显著抑制作用,随LCMO相含量增加,复合样品的超导转变温度逐渐降低,进而失去超导电性.在分析实验数据基础上,我们对铁磁性LCMO相对Bi2212相超导电性的影响进行了研究,并简要探讨了铁磁复合对Bi2212相超导电性抑制机理.     

Bi2212相插层化合物的制备及其应用

我们通过气相输运插层化合反应成功制备了高温超导Bi2212相的碘插层化合物Ix Bi2212，进而制备出碘化汞插层化合物（HgI2）xBi2212．在此基础上，对碘化汞插层化合物（HgI2）xBi2212在丙酮溶液中进行超声剥落，成功制备出了高温超导Bi2212相的纳米粉体．我们对样品进行了表征，并就样品制备技术过程和纳米Bi2212相粉体的应用作了讨论．     

Bi2212相插层化合物的制备及其应用

我们通过气相输运插层化合反应成功制备了高温超导Bi2212相的碘插层化合物IxBi2212,进而制备出碘化汞插层化合物(HgI2)xBi2212.在此基础上,对碘化汞插层化合物(HgI2)xBi2212在丙酮溶液中进行超声剥落,成功制备出了高温超导Bi2212相的纳米粉体.我们对样品进行了表征,并就样品制备技术过程和纳米Bi2212相粉体的应用作了讨论.     

单相Na0.5Bi0.5Ti1-xMnxO3陶瓷中的多铁性

溶胶凝胶法制备了Na0.5Bi0.5Ti1-xMnxO3(x=0,0.02,0.04)陶瓷样品,X射线衍射(XRD)分析表明陶瓷样品均形成了单一的钙钛矿(ABO3)型结构且没有杂质相的形成.随着Mn含量的增加,XRD峰向高角度方向移动,表明Mn离子进入Na0.5Bi0.5TiO3晶格.掺杂样品均表现出室温铁磁性和铁电性.磁测量表明样品中存在复杂的磁相互作用,包括铁磁,反铁磁和顺磁相互作用.以上结果表明,通过Mn的掺杂可以使铁电材料Na0.5Bi0.5TiO3转变为多铁材料.     

系列退火条件下Bi2201相超导电性的进化

通过对Pb掺杂Bi2201相超导样品进行系列条件下的真空退火处理，固定退火时间，调节退火温度，使得样品氧含量随退火温度升高而降低，从而使样品载流子浓度随退火温度升高而依次降低，进而影响样品超导电性．我们系统研究了退火条件、正常态电阻率和超导电性之间的关联，确定了样品最高超导转变温度的退火条件，讨论了Bi2201相超导样品在系列退火条件下其超导电性的进化，并获得了该体系最高超导转变温度Tc^cnset=43K．     

超高压处理对Bi0.8Pb0.2SrCaCu2Oy超导材料的影响

本文研究了超高压影响 Bi 系超导材料超导电性的方式和特点.我们认为,Bi 系材料的2212和2223相在高压切应力作用下发生了结构畸变,从而导致其电磁特性的剧烈变化.对切应力的稳定性随品格参数 C 的增加而减弱.高压处理后的超导样品,品粒有取向排列的趋势.     

系列退火条件下Bi2201相超导电性的进化

通过对Pb掺杂Bi2201相超导样品进行系列条件下的真空退火处理,固定退火时间,调节退火温度,使得样品氧含量随退火温度升高而降低,从而使样品载流子浓度随退火温度升高而依次降低,进而影响样品超导电性.我们系统研究了退火条件、正常态电阻率和超导电性之间的关联,确定了样品最高超导转变温度的退火条件,讨论了Bi2201相超导样品在系列退火条件下其超导电性的进化,并获得了该体系最高超导转变温度Tconset=43K.     

脱氧La0.5Ca0.5MnO3样品的铁磁-反铁磁转变和电阻率变化

研究了氧空位对La0.5Ca0.5MnO3 (LCMO)多晶块材的电输运和磁性质的影响. 随着氧空位的增加, 样品在高温段的电阻率一直增加, 并满足绝热小极化子模型, 而低温段的电阻率先下降后上升, 并出现明显的dR/dT>0的行为, 直至最后变为绝缘的. 氧空位的增加抑止了反铁磁相的出现, 使得脱氧的LCMO样品不发生反铁磁转变, 进一步增加氧空位则会抑制铁磁相.     

Gd掺杂的Bi系2212相单晶电子状态的X射线光电子能谱研究

利用X射线光电子能谱(XPS)研究了Bi系纯2212相超导单晶和Gd掺杂的2212相绝缘体单晶的电子状态的区别。实验结果表明Gd掺杂引起超导电性的变化是由于D_2p轨道空穴填充引起。本文还对Cu2p_3/2XPS卫星峰与主峰强度之比(I_s/I_m),Bi-O层性质以及Bi系Fermi能级附近态密度的来源等问题进行了讨论。 关键词：     

Bi系高温超导体中2212相和2223相的性质分析

本文对 Bi 系中可能存在一种 T_c>100K 的2212相作了进一步的论证.化学分析显示普通的2212相中 Cu~(3+)含量为～10%,而2223相和 T_c>100K 的2212相中 Cu~(3+)的含量却大于30%.从 DTA-TG 实验中观察到普通2212相和2223相失去晶格氧的量为0.8%,而含 T_c>100K 的2212相的样品失去晶格氧的量为～2%,说明这种2212相受氧含量影响更大.文中还介绍了一种简易判断样品中是否存在2223相和普通2212相的经验方法.     

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.     

Doping dependent metal to insulator transition in the (Bi,Pb)-2212 system: The evolution of structural and electronic properties with europium substitution

The present work investigates the effect of europium substitution on the(Bi,Pb)-2212 system in the concentration range 0.5 ≤ x ≤ 1.0.Phase analysis and lattice parameter calculations on the powder diffraction data and the elemental analysis of EDX show that the Eu atoms are successfully substituted into the(Bi,Pb)-2212 system.Resistivity measurements(64-300 K) reveal that the system exhibits superconductivity at x ≤ 0.5 and semiconductivity at x > 0.5.With the complete suppression of superconductivity which is known to be a quasi-two dimensional phenomenon in these materials,a metal to insulator transition takes place at x = 0.6 and the predominant conduction mechanism is found to be variable range hopping between localized states,resulting in macroscopic semiconducting behaviour.The results of electrical and structural properties of the doped(Bi,Pb)-2212 compounds suggest that the decrease of charge carrier concentration and the induced structural disorder are the more effective and dominant mechanisms in the origin of the metal to insulator transition and suppression of superconductivity due to Eu substitution at its Sr site.     

Electrical transport and magnetic properties of La2/3Ca1/3MnO3/SiO2 composites

The influence of SiO₂ on the electrical transport properties of LCMO/SiO₂ composites with different SiO₂ contents x is investigated, where LCMO represents La_2/3Ca_1/3MnO₃. Results show that the SiO₂ phase not only shifts the metal–insulator transition temperature (T_p) to a high temperature range, but also has an effect on the magnetoresistance (MR) of the composites. The temperature dependence of resistivity indicates that the T_p of the composites is obviously higher than that of pure LCMO, and that the peak resistivity ρ_max of the composites is lower than that of pure LCMO. In the SiO₂ content x∼0.02, the T_P is the highest and ρ_max becomes the lowest. The experimental observation is discussed on the basis of the analysis of scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns. Compared with pure LCMO, a possible interpretation is presented by considering the influence of SiO₂ on the coupling between ferromagnetic (FM) domains of LCMO.     

Structure, magnetic and transport properties of La1−xBixMnO3

We have investigated the structural, magnetic and transport properties of La_1−xBi_xMnO₃ samples. As the Bi content increases, a structural transition from rhombohedral to pseudocubic and a magnetic phase transition from ferromagnetic ordering to cluster glass are identified. Metal–insulator (MI) transitions and large magnetoresistance (MR) effects are observed at low Bi doping levels, while insulating behavior of resistivity is found in the whole measured temperature range at high-doping levels. Two distinct ferromagnetic insulating (FI) states are found at low temperatures in this system. One can be suppressed and the other can be enhanced by applying magnetic fields. Possible reasons for the observed structural, magnetic phase transitions and changes of resistivity behavior with Bi doping are discussed.     

低维超导的实验进展

超导自发现以来, 已成为凝聚态物理领域最重要的方向之一. 近年来, 低维材料制备技术的进步使得一维或二维的超导特性实验研究成为可能. 本文在简要介绍超导现象的基础上, 重点回顾了近些年二维超导薄膜和一维超导纳米线的制备和电输运研究, 以及在低维超导体中发现的相移、近邻效应、铁磁超导相互作用和高温超导等新奇的现象, 并对该领域的进一步发展做出了展望.     

Eliashberg analysis of tunneling experiments: support for the pairing glue hypothesis in cuprate superconductors

Evidence for the validity of the pairing glue interpretation of high temperature superconductivity is presented using a modified Eliashberg analysis of experimental superconductor-insulator-superconductor (SIS) tunneling data in B2Sr2CaCu2O8 (Bi2212) over a wide range of doping. This is accomplished by extracting detailed information on the diagonal and anomalous contributions to the quasiparticle self-energy. In particular, a comparison of the imaginary part of the anomalous self-energy ImΦ(ω) and the pairing glue spectral function α2F(ω) used in the model is consistent with Hubbard model simulations in the literature. In addition, the real part of the diagonal self-energy for optimal doped Bi2212 bears a strong resemblance to that obtained from photoemission experiments.     

Rotation of ferromagnetic clusters induced magnetoresistance in the junction composed of La0.9Ca0.1MnO3 +δ and 1 wt.% Nb-doped SrTiO3

A junction composed of ultrathin La0.9Ca0.1MnO3＋δ （LCMO） film and 1 wt.% Nb-doped SrTiO3 was fabricated and its magnetoresistance （MR） was studied and compared with LCMO film. It was found that the resistance of the junction has a similar dependence on magnetic field as that of the LCMO film： the curvature of R-H curves is upward above Curie temperature （Tc） and downward below TC. These behaviours strongly suggest that the rotation of ferromagnetic clusters in manganite also causes MR in the corresponding junction. This MR can be qualitatively understood by the change of the width of the barrier induced by the rotation of ferromagnetic clusters. These results suggest a possibility to obtain junctions with large low-field MR.     

Model for superconductivity in ferromagnetic ZrZn2

We propose that superconductivity in the ferromagnetic state of ZrZn2 is stabilized by an exchange-type interaction between the magnetic moments of triplet-state Cooper pairs and the ferromagnetic magnetization density. This explains why superconductivity occurs in the ferromagnetic state only, and why it persists deep into the ferromagnetic state. The model of this article also yields a particular order parameter symmetry, which is a prediction that can be checked experimentally.     

Coexistence of ferromagnetism and superconductivity in Ni/Bi bilayers

In spite of a lack of superconductivity in bulk crystalline Bi, thin film Bi deposited on thin Ni underlayers are strong-coupled superconductors below approximately 4 K. We unambiguously demonstrate that by tuning the Ni thickness the competition between ferromagnetism and superconductivity in the Ni/Bi can be tailored. For a narrow range of Ni thicknesses, the coexistence of both a superconducting energy gap and conduction electron spin polarization are visible within the Ni side of the Ni/Bi bilayers, independent of any particular theoretical model. We believe that this represents one of the clearest observations of superconductivity and ferromagnetism coexisting.     

Comparative study on the high frequency performances of the easy-plane FeNi@SiO2 powder soft magnetic composite

In this work, an easy-plane FeNi@SiO₂ powder soft magnetic composite (SMC) was imitated and fabricated and its high frequency magnetic properties were comparatively investigated with a non-easy-plane composite. Due to the planar distribution of easy magnetization axes, the easy-plane composite exhibits a constant permeability of 38 up to 100 MHz. Moreover, the easy-plane SMC exhibits a lower core loss at higher frequencies. Loss separated results show that the hysteresis loss plays a dominant loss component in the composite, rather than dominant excess loss in the non-easy-plane powder composite. These results indicate that, compared with non-easy-plane powder composite, the easy-plane powder composites exhibit comprehensive advantages of higher permeability, wider effective operating frequencies and lower loss, which suggest that the use of easy-plane ferromagnetic powder is a promising and efficient measure to develop a new generation of soft magnetic composites for higher frequency application.