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CHINESE JOURNAL OF LOW TEMPERATURE PHYSICS Vol.26 No.1 Feb., 2004 CONTENTS Study of Magnetic Properties and Ion
Size Effect for (La1-xYx)2/3Ca1/3MnO3
(0≤x≤0.3) Manganese……………………………………………………………ZHANG YU-FENG, WANG XIN-YNA, CAO GUI-XIN, LIU YONG-SHENG, JIN CHAO, N NISHIMURA, K MORI, CAO SHI-XUN, ZHANG JIN-CANG (7) Grain Boundary Effect in the Sol-gel Prepared Polycrystalline Manganites……… ……………………………………………………………………………………LI JIAN-QIN (15) Effects of Different Ti Content on NbTi Superconductor′s Critical Current Densities………………………………………………………………XIE BAO-HAI, WU XIAO-ZU, LIU XIANG-HONG, CHEN ZI-LI, PU MING-HUA, LI XIAO-GUANG, CAO LIE-ZHAO, ZHOU LIAN (20) Crystal Structure and Superconductivity of YBa2Cu3O6+x Oxidized by Electrochemical Method……………………………………………………GUO JUAN, CHENG GUO-SHENG, DONG CHENG (25) The Pseudogap Behavior in Electro-doped Sm2-xCexCuO4 Single Crystal……………… …………………………CHAI YI-SHENG, YANG HONG-SHUN, LIU JIAN, YU MIN, CAO LIE-ZHAO (30) Inhomogeneity Introduced by Zn Impurity in Doped Cuprates……………………SONG YUN (34) Research on Strain Effect on Cu-Ni Sheathed MgB2 Superconducting Tape………… ………………………………………………………………………FU MIN-YI, PAN GUO-WEI, JIAO ZHENG-KUAN, DING LI-REN, ZHANG YONG, CHEN ZHI-YOU, HAN HAN-MIN, CHEN JING-LIN (40) A Scanning Squid Microscope and Its Applications for Magnetic Field Imaging and Nondestructive Evaluation…ZHANG FENG-HUI, DING HONG-SHENG, HE YU-SHENG, CHEN GENG-HUA, HAN SHI-JI, DONG SHI-YING, YAN XIAO-MING, YANG QIAN-SHENG, CHENG ZHAO-JIA, JIN DUO (45) The Influence of Nanometer Mg Powder on Preparing MgB2 Superconducting Sample ……………………………FENG QING-RONG, CHEN JIN-PING, XU JU, WANG YU-HAO, CHEN XIN (50) A Preliminary Research of the Magnetic Concentration Device for Scanning Squid Microscope…………………………………………………………………ZHANG FENG-HUI, DING HONG-SHENG, ZHONG CHAO-RONG, HAN SHI-JI, DONG SHI-YING, HE YU-SHENG, S.I.BONDARENKO (55) In Situ Monitoring of the Growth of Complex Oxide Thin Films at High Oxygen Pressures Using a Three stage Pumping Rheed System…………………………………… ………………………CHEN YING-FEI, LI JIE, ZHU XIAO-HONG, WANG PING, ZHENG DONG-NING (60) The Capacitance Equivalent Circuit for Quasi TEM HTS Microstrip and the Basic Capacitance Model………………………………………………… HUANG HUI-FEN, MAO JUN-FA (66) Studies on Some Problems Related to
Pi-ring………………………………XIE FEI-XIANG, DENG PENG, LING JIAN, WANG KE, MA PING, WANG SHOU-ZHENG, WANG FU-REN, DAI YUAN-DONG (71) Study on Conductive Characteristics of ZnO Ceramics Doped Nb2O5 at Low Temperature………………………………………………………JI YUAN-MING, ZHANG JIN-CANG (75) Numerical Study on Stability of HTS Coil Under High Pulse Currents……………… …………………………………………LI YU, LI XIAO-HANG, SONG NAI-HAO, XIAO LI-YE (80) STUDY OF MAGNETIC PROPERTIES AND ION SIZE EFFECT FOR (La1-xYx)2/3Ca1/3MnO3(0≤x≤0.3)
MANGANESE ZHANG YU-FENG1 WANG XIN-YNA1 CAO
GUI-XIN1 LIU
YONG-SHENG1 JIN CHAO1 N NISHIMURA2 K MORI2 CAO SHI-XUN1 ZHANG JIN-CANG1 1Department of
Physics, Shanghai University, Shanghai
200436 2Faculty of
Engineering, Toyama University, Toyama 930-8555, Japan (Received 25
July, 2003; revised manuscript received 15 September, 2003) The magnetic properties of perovskite (La1-xYx)2/3Ca1/3MnO3
(0≤x≤0.3) compounds are systematically investigated and it is given
that the transition temperature Tc is related to average
ion size of La
site. It is found that with the increasing of Y3+ doped content,
the metal-insulator transition temperature TMI (M-I)
shifts to lower temperature. While the relevant resistance peakρp
sharply increases, for the sample of x=0.3, it has enhanced eight
orders of magnitudes larger than the non-doped samples (x=0.0). The
decrease of average ion size of La site and the local distortion of lattice
constant due to the introduction of Y can explain the experimental results.
At high concentration area, say when x>0.1, magnetic studies show a
gradual increase of antiferromagnetic interaction with the
increase of x, ultimately leading to a spin-glass-like state for x=0.2
and x=0.3 compounds at about 35K. Keywords: (La1-xYx)2/3Ca1/3MnO3
perovsksite manganese，magnetic properties，ion size effect PACC: 7550L, 7130, 7530V GRAIN BOUNDARY EFFECT IN THE
SOL-GEL PREPARED POLYCRYSTALLINE MANGANITES LI JIAN-QIN Department of
Physics, Wuhan University of Technology, Wuhan 430070 The temperature dependence of resistivity obtained
in the sol-gel prepared polycrystalline La2/3Ca1/3MnO3
samples is quantitatively studied in terms of a model recently proposed for
ferromagnetic metallic granular systems. From this study, the grain boundary
effect on the electrical transport is discussed for polycrystalline
manganites. Keywords: grain boundary, spin-polarized tunneling,
electronic transport PACC: 7530V, 7340R, 7570C EFFECTS OF DIFFERENT Ti CONTENT ON
NbTi SUPERCONDUCTOR′S CRITICAL CURRENT
DENSITIES XIE BAO-HAI12 WU XIAO-ZU2 LIU XIANG-HONG2 CHEN ZI-LI2 PU MING-HUA2 LI XIAO-GUANG3 CAO
LIE-ZHAO3 ZHOU
LIAN2 1Northeastern
University, Shenyang 110004 2Northwest
Institute for Nonferrous Metal Research, Xi′an 710016 3University of
Science and Technology of China, Hefei
230026 Three different compositions of NbTi wires have
been fabricated by using alternately niobium sheets and titanium sheets. The
Ti content may vary from 43WT% to 57WT% by adjusting the relative thickness
of the Nb and Ti sheets in the monofilaments. The effects of different Ti
content on NbTi superconductor′s critical current densities and flux pinning
mechanism were discussed. The Nb/Ti interface microstructure and
cross-sectional morphology diffusion have been investigated by scanning
electron microscopy (SEM). The curve of Fp∝B at different
composition have been fitted. The results show that the critical current
density (Jc) can be improved with higher Ti content in the
low field rang(<5T), but the property was weak and rapidly fall in the
high field. There are two kinds of flux pinning mechanism dot pinning and
subface pinning affect the property in different field. Keywords: NbTi superconductor, critical current densities
(Jc), flux pinning PACC: 7470L, 7460M CRYSTAL STRUCTURE AND
SUPERCONDUCTIVITY OF YBa2Cu3O6+x OXIDIZED BY ELECTROCHEMICAL METHOD GUO JUAN1,2 CHENG GUO-SHENG1,2,3 DONG CHENG1 1National Lab.
for Superconductivity, Institute of Physics, Chinese Academy of Sciences,
Beijing 100080 2Department of
Physics, Henan Normal University, Xinxiang 453002 3Department of
Physics, Nanjing Institute of Meteorology 210044 (Received 10
April, 2003) The electrochemical oxidation was performed on
oxygen deficient YBa2Cu3O6+x (x～0.1)
bulk samples prepared by solid-state method. The oxidation on anode was
carried out in molten KNO3-NaNO3 at 360℃. The samples
oxidized electrochemically were characterized by resistance, magnetic
susceptibility measurements and XRD analysis. The superconducting volume
fraction increases with oxidation time and charge passed through samples.
Using this method, we can obtain samples with single superconducting 60K
phase or 90K phase and samples containing these two phases. The results of
XRD analysis reveal that the structure of outer layer and inter layer is
different indicating that the distribution of oxygen in samples is
inhomogeneous. Keywords: electrochemical oxidation, YBCO, crystal
structure, superconductivity PACC: 7470V, 8280F, 6110 THE PSEUDOGAP BEHAVIOR IN ELECTRO-DOPED Sm2-xCexCuO4
SINGLE CRYSTAL CHAI YI-SHENG YANG HONG-SHUN LIU JIAN YU MIN CAO LIE-ZHAO Structrual
Research lab, Physics Department, University of Science and Technology y of China,
Hefei, Anhui 230026 (Received 10
April, 2003) The pseudogap-like behavior has been observed in
electro-doped superconductor Sm1.85Ce0.15CuO4
for the first time. The resistivity ρ and thermopower S of
single crystal Sm1.85Ce0.15CuO4 with
different annealing times were measured. The data of temperature dependence
of resistivity indicate that the high temperature resistivity ρ, dρ/dT
and the slope of thermopower dS/dT increase with increasing
annealing time, which presume a decrease of charge density and act as the
decrease of Ce content x. In each annealing procedure, the curve of S～T
and ρ～T change their slopes below a certain temperature T*.
It moves to high temperature region with increase annealing time, and becomes
more and more clear, indicating the opening of a pseudogap under this
temperature. At the same time, a minimum value exists in the thermopower at
certain temperature, which is the manifest of carrier localization. At about
50K, a clear peak of phonon-drag was observed in thermopower, and its
positive value shows a change of sign in charge carrier at low temperature,
which is in accordance with the change of slope in Hall coefficients.
Keywords: perovskite phase superconductors, transport properties,
thermoelectric power PACC:
7470V, 7430F, 7430J
INHOMOGENEITY INTRODUCED BY Zn IMPURITY IN DOPED CUPRATES SONG YUN Department of
Physics, Beijing Normal University, Beijing 100875 (Received 11
April, 2003) Two-dimensional t-J model with nonmagnetic
Zn impurities is studied based on the fermion-spin theory. Within an improved
Green function theory, we perform numerical calculation for the finite lattices with periodic
boundary conditions, and obtain the inhomogeneities of hole concentration and
local antiferromagnetic correlations around the nonmagnetic Zn impurities. It
is shown that the spin excitations are strongly influenced by the nonmagnetic
impurities because the local antiferromagnetic correlations closest to the
impurities are enhanced. The nearest-neighbor spin correlations also have
strong effect to the energy of hole, as a result a bound state of hole is
formed around the nonmagnetic -c Zn impurity. Keywords：t-J model, fermion-spin theory, Zn impurity PACC:
7420M, 7430J, 7540M RESEARCH ON STRAIN EFFECT ON Cu-Ni SHEATHED MgB2
SUPERCONDUCTING TAPE 1Physics
Department of Zhejiang University, Hangzhou 310027 2Institute of
Plasma Physics, Chinese Academy of Science, Hefei 230031 (Received 11
April, 2003) The elastic modulus measurements of Cu-Ni sheathed
MgB2 monofilament tape fabricated by “power in tube” method have been
performed using electric technique. The magnetic field dependence of Ic
has been investigated on the sample subjected to various strain levels
through bending of the tape with different radius. We found that our MgB2
sample is sensitive to applied strains, mechanical reinforced MgB2
tape is essential to practical application. The bend strain and stress have
been calculated based on a formula derived from the definition. Keywords: MgB2 monofilament, Strain effect, Dynamics
process of quench PACC: 7430L, 7470 A SCANNING SQUID MICROSCOPE AND ITS
APPLICATIONS FOR MAGNETIC FIELD IMAGING AND
NONDESTRUCTIVE EVALUATION ZHANG FENG-HUI1 DING HONG-SHENG1,2 HE YU-SHENG1 CHEN
GENG-HUA1 HAN SHI-JI1 DONG SHI-YING1 YAN
XIAO-MING3 YANG
QIAN-SHENG1 CHENG
ZHAO-JIA1 JIN
DUO1 1Institute of
physics, Chinese Academy of Sciences, Beijing 100080 2Department of
Physics, University of Science and Technology Beijing 100083 3Technical
Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100080 (Received 11
April, 2003) We have built two scanning SQUID microscope for
room temperature samples with LTS SQUID and HTS (YBCO) SQUID respectively.
SQUIDs are mounted on the low end of the finger in Dewar. A thin sapphire
window separates SQUIDs and samples. Samples stay in room temperature. The
distance between SQUIDs and samples can be adjusted with a bellow. The LTS
SQUID microscope has a field sensitivity superior to 3pT/Hz1/2 and
spatial resolution better than 140μm. The HTS SQUID system is of ～46pT/Hz1/2
field sensitivity and ～500μm spatial resolution. Both microscopes can stably
work for a long time in unshielded environment. We also have used them to do
some interesting experiments for magnetic field imaging and nondestructive evaluation (NDE). Keywords: SQUID, microscope, magnetism imaging, nondestructive
evaluation PACC: 0755, 8170L THE INFLUENCE OF NANOMETER Mg
POWDER ON PREPARING MgB2
SUPERCONDUCTING SAMPLE FENG QING-RONG CHEN JIN-PING XU JU WANG YU-HAO CHEN XIN Department of Physics and State Key Laboratory of
Artificial Microstructure and Mesoscopic Physics, Peking University,
Beijing 100871 (Received 10 April, 2003) MgB2
superconducting sample, with nanometer magnesium powder and boron powder as
raw materials (hereafter referee as to nano-MgB2 superconducting
sample), was prepared at ambient pressure. A set of in-situ ρ-T curves
were obtained It is different from those in-situ ρ-T curves obtained
for the MgB2
superconducting samples, with ordinary off-the-shelf powder and boron powder
as the raw materials (hereafter referee as to ordinary-MgB2
superconducting sample) prepared in the vacuum and flowing argon atmosphere
respectively. The experimental results indicated that the temperature of
formation MgB2-phase of nano-MgB2 superconducting
sample is between 430℃ and 490℃. It is lower than the temperature of
formation MgB2-phase of ordinary-MgB2 superconducting
sample sintered in vacuum and argon atmosphere: 640℃～700℃ and 530℃～630℃
respectively. The density of nano-MgB2 superconducting sample is
1.46g/cm3, and is higher than the densities of other MgB2
superconductin g sample sintered for one time. Keywords: Nano
Mg powder, MgB2 superconductor, SEM graph, X-ray diffraction PACC: 7400, 7430, 7490, 7470Y A PRELIMINARY RESEARCH OF THE
MAGNETIC CONCENTRATION DEVICE FOR SCANNING SQUID
MICROSCOPE ZHANG
FENG-HUI1 DING
HONG-SHENG1,2 ZHONG
CHAO-RONG1,3 HAN
SHI-JI1 DONG
SHI-YING1 HE YU-SHENG1 S.I.BONDARENKO1 1Institute of physics,
Chinese Academy of Science, Beijing
100080 2Department of Physics,
university of Science and Technology Beijing,Beijing 100083 3Department of Physics,
Chongqing University, Chongqing
400044 4Institute for Low
Temperature Physics and Engineering, Kharkov, Ukraine The properties
of the magnetic concentration device (i.e. the concentrator) have been
investigated for the potential application in scanning SQUID microscope. It
was suggested that the feature of the concentrator can be characterized by a
concentration parameter K, and a simple model is then proposed, of
which K is dependent on the magnetic permeability of the material and
the demagnetization factor of the device. Systemic studies of permalloy wire
with 0.1mm diameter have been carried out. Experimental results of
dependences of the concentration parameter on device length and excited field
(current) were obtained, respectively. It was established that the
theoretical model can give a good description of the characteristic feature
of the concentrator qualitatively. Keywords: ferromagnetic
concentrator, concentration parameter, magnetic permeability, demagnetization
factor PACC: 0755, 8170L IN SITU MONITORING OF THE GROWTH OF
COMPLEX OXIDE THIN FILMS AT HIGH OXYGEN PRESSURES
USING A THREE-STAGE PUMPING RHEED SYSTEM CHEN
YING-FEI LI JIE ZHU XIAO-HONG WANG
PING ZHENG DONG-NING National
Laboratory for Superconductivity, Institute of Physics, CAS, P. O. Box 603,
Beijing 100080 (Received 10
April, 2003) We have successfully developed a high-pressure
RHEED accessory with a three-stage differential pumping system for the PLD
equipment in our laboratory. It can be used for in situ monitoring during the
deposition of complex oxides at standard PLD conditions. Oxygen pressure in
the deposition chamber can be increased to as high as 21Pa while fairly clear
RHEED patterns are observable. We monitored the deposition of SrTiO3:Nb, Ba0.5Sr0.5TiO3, and YBa2Cu3O7 single layers, as well as Ba0.5Sr0.5TiO3/SrTiO3:Nb heterostructure on (001) SrTiO3 substrates. Pattern analyses suggest that all the films are epitaxy with good crystallinity; however the growth mode and film morphology are greatly affected by the ambient during film deposition. In high vacuum, the film tends to grow in the layer-by-layer mode, and the surface roughness is within nanometers; in an oxygen pressure of 5Pa or above, however, the film tends to grow in the island mode with less smooth surface. It is revealed that, in the case of multilayer growth, the crystallinity and surface smoothness of the top layer are limited by the quality of the bottom layer. Keywords: RHEED， Epitaxial Growth, High-Tc
Superconductor PACC:
7475 THE CAPACITANCE EQUIVALENT CIRCUIT
FOR QUASITEM HTS MICROSTRIP AND THE BASIC
CAPACITANCE MODEL HUANG HUI-FEN MAO JUN-FA (Received 29
May, 2003; revised manuscript received 9 September, 2003) In this paper the capacitance equivalent circuits
of quasi-TEM HTS microstrip have been presented for thick and thin conductors
according to the distribution of magnetic field and current density in
superconductor thick and thin films, and the basic capacitance expressions
have been given. The expressions are verified by using them to analyze three
examples. Keywords: HTS, microstrip, Capacitance PACC:
7360K, 7300, 8140 STUDIES ON SOME PROBLEMS RELATED TO
PI-RING XIE
FEI-XIANG DENG PENG LING
JIAN WANG
KE MA PING WANG SHOU-ZHENG WANG FU-REN DAI YUAN-DONG Mesoscopic
Physics National Laboratory and Department of Physics, Peking Univers ity,
Beijing 100871 (Received 11
April, 2003) We concluded our work related to the principle and
the possible application of the spontaneous magnetization in a π ring.
Temperature dependence has been deduced which fits the experimental data
well. We analyzed a design of a π ring based rapid single flux quantum
trigger unit without a continuous bias current and got the suitable working
regime. The free energy of a coupled double π ring has been
calculated. The result showed that reverse direction coupling has a lower
energy. And without magnetic coupling, the quantum interference effect will
also lead to reverse direction coupling. Keywords: π- ring, spontaneous magnetization,
forth-ordered Runge-Kutta method PACC:
7400, 7490 STUDY ON CONDUCTIVE CHARACTERISTICS
OF ZnO CERAMICS DOPED Nb2O5
AT LOW TEMPERATURE JI YUAN-MING1 ZHANG JIN-CANG2 1Ching University
of Ming and Technology, Beijing
100083 2Shanghai University,
Shanghai 200436 This paper presents the results of the study of
ZnO conductive ceramics doped with Nb2O5 at low
temperature. The experiment results show that with the increasing of Nb2O5
contents, resistivity reduced at low temperature. The higher sintering
temperature, the smaller resistivity is for ZnO samples in different
sintering temperatures. As the sintering time increased, the resistivity
decreases at the same sintering temperature. Keywords: ZnO ceramics, conductiv characteristics, doped, low
temperature PACC:
7480T, 7490 NUMERICAL STUDY ON STABILITY OF HTS COIL UNDER HIGH PULSE CURRENTS LI YU LI XIAO-HANG SONG NAI-HAO XIAO LI-YE Applied
Superconductivity Laboratory PO Box 2703, Institute of
Electrical Engineering Chinese Academy of Sciences, Beijing 100080 (Received 9
April, 2003) In high temperature superconducting (HTS) coil,
the loss of stability may be result of the accumulation of heat, which can be
generated from the flux-flow resistance, AC losses and normal-zone
resistance. Hence the stability of a HTS coil under high pulse currents is a
key problem. In this paper, a numerical model was set up to simulate the heat
generation and quench propagation after a high pulse current was applied. The
temperature distribution as a function of time in the coil was calculated.
The simulation is in good agreement with the experimental results. In the AC
cases, a maximum “safe” current can be calculated from our simulation, which
will be very helpful for the design of HTS AC magnets and transformers. Keywords: High temperature superconducting coil, stability, numerical
simulation PACC:
7470p, 7490 |