低温物理学报

CHINESE JOURNAL OF LOW TEMPERATURE PHYSICS

Vol.26 No.3 Aug., 2004　

CONTENTS

Study of Transport Properties and Abnormal Magnetic Properties for

(La_1-xCe_x)_2/3Ca_1/3MnO₃ System……………………………………………WANG XIN-YAN,

CAO SHI-XUN, ZHANG YU-FENG, TUBATA KEN, CUI YU-JIAN, LIU YONG-SHENG,

CAO GUI-XIN, NISHIMURA KATSUHIKO, MORI KATSUNORI, JING CHAO, ZHANG JIN-CANG (182)

Study of Structure and Magnetic Properties at Low-Temperature for Bi-Mn

Alloys Fabricated by Magnetic Field Inducement…JIA GUANG-QIANG, ZHANG JIN-CANG,

LIU YONG-SHENG, REN ZHONG-MING, CAO SHI-XUN, LI XI, JING CHAO, DENG KANG (189)

Growth, Structure and Properties of Na_xCoO₂ Crystals…………………………

………………………… CHEN XUE-ZHI, SHEN JING-QIN, ZHAO SONG-RUI, XU ZHU-AN (193)

Equivalence of London's Equations and Discussion about Critical State Bean

Model………………………………………HAN YONG-SHENG, CHEN SHU, YANG HONG-XIN (198)

Transport Property Of Nd_2-xSr_xNiO₄ Poly Crystals…………YU YONG, RUAN KE-QING,

HUANG SHENG-LI, QIAN SHUO, CHAI YI-SHENG, YANG HONG-SHUN, CAO LIE-ZHAO (204)

Monte Carlo Simulation of the Temperature Dependence of Resistance for

Polycrystalline La_2/3Ca_1/3MnO₃ with Different Grain size………………………

…………………………………………………LI JIAN-QING, TIAN XU, ZHANG XIAO-LING (209)

Influence of Pb Substitution and I Insertion Layer on Structure and Properties

in Bi₂Sr₂Co₂O₈ System … WANG HANG-DONG, WAN HAI-YANG, LIN YANG-FAN, FANG MING-HU (215)

Entanglement Between Molecular Magnet and Environment and Decoherence……

………………………………… NIE YI-HANG, ZHAO HUA, LIANG JUN-JUN, LIANG JIU-QING (222)

Superfluid Phase of Bose-Einstain Condensation In Optical lattice…………

………………………………………………………… LIANG JUN-JUN, LIANG JIU-QING (226)

Experiment on Fiber Bragg Grating Strain Sensor for Cryogenic Environment

………………………………… FENG ZUN-AN, WANG QIU-LIANG, DAI FENG, HUANG GUO-JUN (231)

Low Temperature Scanning Microwave Near-Field Microscope and Its Application

on Material Research…… ………………… JIANG TIAN, WU LI-YONG, FENG YI-JUN (236)

Experimental Measurement and Analysis on Anisotropy Characteristic of the

Critical Current in Bi-2223/Ag HTS Tapes………………………………………

WANG CHAO, HUANG HUI, SONG SHOU-SEN, ZHANG BO, YANG MING, WANG QIU-LIANG (242)

Influence Of Regnerator Flow Resistance On Stability Of Pulse Tube Cooler

…………………………………JIANG YAN-LONG, CHEN GUO-BANG, GAN ZHI-HUA, G.THUMMES (250)

Effects Of Oxygen Deficiency On The Magnetization And Resistivity In

La_0.7Ca_0.3Mn_0.92Cr_0.08O_3-δ ………………………………………………………………

TIAN JIAN-JUN, FANG JUN, WANG FANG, HUANG ZHEN, CHEN ZHI-YOU, CHEN JING-LIN (256)

Interaction Between Layers In Manganese Perovskite Films……………………

………………………………………………FENG WEN, XIA ZHENG-CAI, YUAN SONG-LIU (262)

HTS Bandstop Filter with Novel Structure and High Skirt Selectivity………

……………………………SUN LIANG, CHEN JING, LI SHUN-ZHOU, HUANG JIAN-DONG,

YIN ZHENG-CHAO, LI CHUN-GUANG, HE AI-SHENG, ZHANG XUE-QIANG, LI HONG,

LUO SHENG, GU CHANG-ZHI, JIN AI-ZI, YANG HAI-FANG, FENG JI, HE YU-SHENG (267)

Enhancement Of Low-Field Magnetoresistance In La_0.67Ca_0.33MnO₃/Cu Composites

……………… TANG JIE, LIU SHENG, ZHANG GUO-HONG, ZHANG LI-JIANG, YUAN SONG-LIU (272)

STUDY OF TRANSPORT PROPERTIES AND ABNORMAL MAGNETIC

PROPERTIES OF (La_1-xCe_x)_2/3Ca_1/3MnO₃ SYSTEM　

WANG XIN-YAN¹⁾CAO SHI-XUN¹⁾ ZHANG YU-FENG¹⁾ TUBATA KEN²⁾ CUI YU-JIAN³⁾ LIU YONG-SHENG¹⁾ CAO GUI-XIN¹⁾

NISHIMURA KATSUHIKO²⁾ MORI KATSUNORI²⁾ JING CHAO¹⁾ ZHANG JIN-CANG¹⁾

^{1)Department of Physics , Shanghai University , Shanghai 200436 , China
^{2)Faculty of Engineering , Toyama University , Toyama 930-8555, Japan}}^{3)
Department of Physics, China Institute of Metrology , Hangzhou 310034 , China

( Received 27 October,2003;revised manuscript received 12 January,2004 )
This paper reported the transport properties and abnormal magnetic properties in Ce doped manganese (La_1-xCe_x)_2/3Ca_1/3MnO₃ (x=0~1.0) polycrystalline samples. The results show that Ce doping drives T_C to lower temperature, on the whole the resistivity rises and show tremendous MR effect under applied magnetic field. Two anomalies were found in the DC magnetize measurements, the peak at higher temperature signifies the PM to FM transition of the Mn spins and the other at lower temperature signifies the ordering of Ce spins. Ce doping induces the competition between the double exchange and superexchange, and the coupling between Ce and Mn spins is quite strong. With increasing Ce content, the Mn ordering temperature decreases and the Ce ordering temperature shifts to a little higher temperature, thus the FM area reduces and becomes indistinct for x≥0.5 samples.
Keywords: Perovskite Manganite，Ce doping，Magnetic Properties

PACC: 7530E，7220M，7215G
　

STUDY OF STRUCTURE AND MAGNETIC PROPERTIES AT LOW-TEMPERATURE FOR Bi-Mn ALLOYS FABRICATED BY MAGNETIC FIELD INDUCEMENT

JIA GUANG-QIANG¹⁾ ZHANG JIN-CANG¹⁾ LIU YONG-SHENG¹⁾ REN ZHONG-MING²⁾}

CAO SHI-XUN¹⁾ LI XI²⁾ JING CHAO¹⁾ DENG KANG²⁾

1)Department of Physics, ²⁾Department of Materials Science and Engineering,

Shanghai University, Shanghai 200436

( Received 25 January, 2004 )

The Bi-Mn wt6% alloys are solidified from semi-solid state in a magnetic field. The microstructure and magnetic properties have been studied systematically at low temperature. The results show that the samples are eutectic system of double phase and have large anisotropy. It was shown that alignment of MnBi crystals along the applied field occurred. Magnetic measurements show c axis of MnBi is parallel to the applied field. The coercivity increases with the increasing temperature and exhibits a positive temperature coefficient; but the saturation magnetization decreases with the increasing temperature. The spin reorientation temperature T_SR for MnBi alloys decreases with increasing measure magnetic field and the peak shape becomes wide. When the magnetic field increases to above 1T, the spin reorientation phenomena vanish in the present experiment. The characteristic temperature T_SR increases with the increasing induced magnetic field.

Keywords: preparation technology induced by magnetic field, Bi-Mn alloy, magnetic properties at low temperature, spin reorientation

PACC: 0720M, 7500, 3520M

GROWTH, STRUCTURE AND PROPERTIES

OF Na_xCoO₂ CRYSTALS

HEN XUE-ZHI SHEN JING-QIN ZHAO SONG-RUI XU ZHU-AN

Department of Physics, Zhejiang University, Hangzhou 310027

(Received 15 October, 2003)

γ- and α-phase Na_xCoO₂ crystals have been grown by a electrosynthesis method. By adding SrCO₃ to the flux, the Na_xCoO₂ crystal can be selected to grow into different phase. Crystals grown from a flux of pure NaOH and crystals grown from a flux of NaOH mixed with SrCO₃ were identified as by X-ray diffraction (XRD) γ- Na_xCoO₂ and α- Na_xCoO₂ respectively. The in-plane electrical resistivity of α- Na_xCoO₂increases with decreasing temperature, exhibiting the semiconductor properties, while that of γ- Na_xCoO₂ decreases with decreasing temperature, exhibiting the metal properties. The in-plane thermoelectric power S(T) of α-Na_xCoO₂ is lower than that of γ-Na_xCoO₂. The S(T) at 300K is 30μV/K for α-Na_xCoO₂ and 70μV/K for γ-Na_xCoO₂, and both decrease with decreasing temperature.

Keywords：Crystal growth，thermoelectric power, thermoelectric material

PACC： 8110，7220P，5225F

EQUIVALENCE OF LONDON'S EQUATIONS AND

DISCUSSION ABOUT CRITICAL STATE BEAN MODEL

HAN YONG-SHENG^1,2 CHEN SHU¹ YANG HONG-XIN¹

^{1Department of Fundamental Science, China Pharmaceutical University, Nanjing 210009
^{2Department of Physics and National Laboratory of Solid State Microstructure, Nanjing University, Nanjing 210093}}

(Received 5 April,2004)

Near 40 years ago, Bean established the remarkable critical state theory of the hard superconductors based on the K. Mendelssohn sponge model. This theory became the fundamental theory for the hard superconductor electromagnetic properties. Recently, the study of the critical state dynamics has achieved great advance based on the development of vortex dynamics. The basis of Self-organized criticality physics is the strong nonlinear effects, such as local Joule heat and vortex motion which leads to the phase sliding of macro wave function. Some experiments illustrate that the flux front is linear distribution as the flux penetrates into the superconductor. Its analytic interpretation is under development. In this article, we deal with this subject based on London's theory and Anderson's flux motion model, and illustrate the electrical field distribution, current density and magnetic field distribution in the sample.

Keywords: Bean model, Slab sample, vortex Dynamic, flux density distribution

PACC: 7420M, 7420D

TRANSPORT PROPERTY OF

Nd_2-xSr_xNiO₄POLY CRYSTALS

YU YONG RUAN KE-QING HUANG SHENG-LI QIAN SHUO

CHAI YI-SHENG YANG HONG-SHUN CAO LIE-ZHAO

Structure Research laboratory , Department of Physics , University of Science and

Technology of China , Hefei , Anhui 230026

(Received 15 April,2004)

The transport property of Nd_2-xSr_xNiO₄ poly crystals with various Sr content is studied. For 0<x≤0.5, the temperature dependence of resistivity is well fitted with variable-range-hopping(VRH) formula. Nd_2-xSr_xNiO₄ (0.8≤x≤1.1) exhibit metallic-like behavior above room temperature and show metal-insulator transition with the decreasing of temperature below room temperature. For x=1.4, the resitivity remains metallic down to 14K. The thermopower for x=1.4 is interpreted very well by the VRH mechanism.

Keywords: transport property , VRH , metal-insulator transition

PACC: 7280G, 7280T

MONTE CARLO SIMULATION OF THE TEMPERATURE DEPENDENCE OF RESISTANCE FOR POLYCRYSTALLINE La_2/3Ca_1/3MnO₃ WITH DIFFERENT GRAIN SIZE

LI JIAN-QING TIAN XU ZHANG XIAO-LING

Department of Physics, Wuhan University of Technology, Wuhan 430070

(Received 25 February, 2004)

Polycrystalline La_2/3Ca_1/3MnO₃ samples with different grain size were prepared in a sol-gel method. Electronic transport behavior was studied by measuring resistance as a function of temperature. Based on the random resistor network model generated through the Monte Carlo method, the temperature dependence of resistance is simulated for samples with different grain size, which yields excellent agreement with the experimental data. Based on this simulation, the grain boundary effect on the electronic transport behavior is discussed.

Keywords: manganite perovskite, grain boundary effect, random resistor network

PACC: 7530V,7340R,7570C　

INFLUENCE OF Pb SUBSTITUTION AND I

INSERTION LAYER ON STRUCTURE AND

PROPERTIES IN Bi₂Sr₂Co₂O₈ SYSTEM

WANG HANG-DONG, WAN HAI-YANG, LIN YANG-FAN, FANG MING-HU

Department of Physics, Zhejiang University, Hangzhou 310027

（Received 10 October, 2003）

Since the discovery of superconductivity in Na_xCo₂O₄+yH₂O compound in March, much attention had been focused on the cobalt compounds that contain hexangular CoO₂ layers. In this paper, the polycrystalline samples of Bi_2-xPb_xSr₂Co₂O₈ (x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) were synthesized. And iodine was successfully inserted between Bi-O layers in these samples. It was found that their c axis length increased from 1.49nm to 1.87nm. The studies on their structure, transport properties and magnetic properties were systematically carried out. A spin-glass transition at about 4K was observed in all the Pb-doped samples. With the insertion of iodine between Bi-O layers, the sample turns into a semiconductor instead of a superconductor, and also shows the spin-glass behavior at low temperature. The effects of Pb partial substitution and I insertion were discussed in detail.

Keywords: cobalt oxide, spin glass, transition-metal oxide

PACC: 7550L, 7280G

ENTANGLEMENT BETWEEN MOLECULAR

MAGNET AND ENVIRONMENT AND DECOHERENCE

NIE YI-HANG ZHAO HUA LIANG JUN-JUN LIANG JIU-QING

^{1Institute of Theoretical Physics, Shanxi University, Taiyuan 030006
^{2Department of Physics, Yanbei Normal Institute, Datong 037000}}

(Received 13 October, 2003)

We study the coherent quantum tunneling in a biaxial molecular magnet with dissipation of the environment which results in the suppression of the tunneling and therefore the decoherence of Schrodinger cat states in molecular magnet. The interphonon interaction leads in an effective decoupling of the spin system from the phonon bath and therefore decreases the entanglement and decoherence. The degree of entanglement between the magnet and environment is evaluated explicitly with the help of reduced density matrix under adiabatic and nonadiabatic approximation. When the entanglement approaches maximum value the coherent tunneling is suppressed completely.

Keywords： molecular magnet, coherent tunneling, decoherence, entanglement

PACC： 7335, 3640, 7170

SUPERFLUID PHASE OF BOSE-EINSTAIN　

CONDENSATION IN OPTICAL LATTICE

LIANG JUN-JUN LIANG JIU-QING

Institute of Theoretical Physics, Shanxi University, Taiyuan, 030006

( Received 11 October ,2003)

The energy spectrum of Bose-Einstein Condensation in optical lattice is analyzed by Bogliubov method. It is explicitly pointed out that such system is a typical superfluid state the velocity of superfluid is given out.

Keywords: Bogliubov transform, superfluid phase superfluid-Mott insulator phase transition

PACC: 0530J，6490，6700

EXPERIMENT ON FIBER BRAGG GRATING STRAIN

SENSOR FOR CRYOGENIC ENVIRONMENT

FENG ZUN-AN^1,2 WANG QIU-LIANG¹

1Institute of Electrical Engineering，CAS，Beijing 100080
^{2Graduate School of the Chinese Academy of science, Beijing 100039}
DAI FENG³ HUANG GUO-JUN³
^{3Institute of Mechanics，CAS，Beijing 100080}
（ Received 21 December,2003;revised manuscript received 9 January,2004）

Experiments on fiber-Bragg Grating Strain Sensor at liquid nitrogen temperature are presented. Based on the principle of the Fiber Bragg Grating Sensor the fiber-Bragg static transmission property was tested at liquid nitrogen temperature. The calibration of the fiber-Bragg grating strain sensor is given. The λ-ε curve was established.

Keywords: liquid nitrogen temperature, strain, fiber-Bragg Grating

PACC: 0710；0630M

LOW TEMPERATURE SCANNING MICROWAVE

NEAR-FIELD MICROSCOPE AND ITS

APPLICATION ON MATERIAL RESEARCH

JIANG TIAN WU LI-YONG FENG YI-JUN

Department of Electronic Science and Engineering, Nanjing University, Nanjing 210093

（ Received 15 December,2003;revised manuscript received 22 December,2003）

Microwave near-field technique has been proved to be an effective tool for studying the local microwave properties of materials. In this paper, we present our low temperature scanning microwave near-field microscope system by combining the microwave near-field technique with a precisely designed low temperature sample stage. Using this system, we have investigated the local temperature dependent microwave properties of YBaCuO superconducting thin film and NdSrMnO magnetic thin film. From the experimental results, we believe that this instrument will be very helpful in the measurement of the local microwave properties of electronic materials.

Keywords: microwave near-field technique, nondestructive testing, superconducting thin film, magnetic material

PACC: 8170L,7360K,7570　

EXPERIMENTAL MEASUREMENT AND ANALYSIS ON ANISOTROPY CHARACTERISTIC OF THE CRITICAL CURRENT IN BI-2223/AG HTS TAPES

WANG CHAO^1,2 HUANG HUI¹ SONG SHOU-SEN¹

ZHANG BO¹YANG MING¹ WANG QIU-LIANG¹
^{1Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing, 100080
^{2Graduate School of the Chinese Academy of Sciences, Beijing, 100039}}

（ Received 25 December,2003）

A method for measuring the anisotropic characteristic of the critical current in the Bi-2223/Ag tape is proposed in this paper. The experimental result reveals that the critical current in the Bi-2223/Ag tape varies with the magnitude of external magnetic field under different orientations of external magnetic field applied to the tape surface. The high sensitivity of the critical current in the Bi-2223/Ag tape to the perpendicular component of magnetic field on the tape, which is caused by the high anisotropy of this kind of materials, is a disadvantage for its electric power applications such as HTS magnets.

Keywords: Bi-2223/Ag tape, critical current, anisotropy

PACC: 0630L 0720M 7430F 7460J

INFLUENCE OF REGENERATOR FLOW RESISTANCE ON

STABILITY OF PULSE TUBE COOLER

JIANG YAN-LONG^1，2 CHEN GUO-BANG² GAN ZHI-HUA² G.THUMMES³
^{1Department of Man-Machine and Environment Engineering,

Nanjing University of Aeronautics and Astronautics, Nanjing, 210016
^{2Cryogenics laboratory, Zhejiang University, Hangzhou, 310027
^{3Institute of Applied Physics, University of Giessen, 35392, Germany}}}

（ Received 27 November,2003）

The DC flow induced by the double-inlet in a pulse tube cooler is the main reason of temperature instability. The possibility of utilizing regenerator flow resistance to suppress DC flow is theoretically and experimentally investigated. Both results show that with a proper larger regenerator flow resistance, DC flow could be suppressed to a smaller extent. Then a long-time operation of the cooler with a stable temperature output at 80K temperature region could be carried out.

Keywords: regenerator flow resistance, DC flow, stability

PACC: 0720M

EFFECTS OF OXYGEN DEFICIENCY ON THE MAGNETIZATION AND

RESISTIVITY IN La_0.7Ca_0.3Mn_0.92Cr_0.08O_3-_δ

TIAN JIAN-JUN FANG JUN WANG FANG HUANG ZHEN CHEN ZHI-YOU CHEN JING-LIN

High Magnetic Field Laboratory , Institute of Plasma Physics,

Chinese Academy of Sciences, Hefei 230031

( Received 17 July, 2003)

A series of La_0.7Ca_0.3Mn_0.92Cr_0.08O_3-δ polycrystalline samples with different oxygen content have been prepared by different ways of cooling. It was found that, in contrast to the nearly stoichiometric oxygen-content samples, the oxygen-deficient compounds have double bumps in resistivity with only one magnetic transition. It was explained in terms of electronic and magnetic phase separation due to inhomogeneous distribution of oxygen content in the samples. Moreover, the phase separation picture was used to explain another trait of Cr doping: Cr is less potent in lowering T_c, compared with other doping elements.

Keywords: perovskite manganites, Mn-site doping , oxygen content, double resistivity bumps , phase separation

PACC: 7470V, 6170T, 9850E , 7200 , 6480

INTERACTION BETWEEN LAYERS

IN MANGANESE PEROVSKITE FILMS

FENG WEN XIA ZHENG-CAI YUAN SONG-LIU

Department of Physics, Huazhong University of Science and Technology, Wuhan 430074

( Received 20 October, 2003)

High quality La_0.67Ca_0.33MnO_3-d/ La_0.67Sr_0.33MnO_3-d/ La_0.67Ca_0.33MnO_3-d(LC/LS/LC) trilayered films have been achieved on LaAlO₃ (100) substrates by means of dc magnetron sputtering technique. The electrical resistivities versus temperature of the films were measured with a standard four-probe method. Results show that, for a given LC, with the increase of the thickness of LS, the zero-field resistivity (ρ) decreases and metal-insulator transition temperature (T_M-I) increases; for a given LS, with the increase of the thickness of LS, the zero-field resistivity (ρ) decreases and metal-insulator transition temperature (T_M-I) also increases. Based on the double-exchange (DE) mechanism, the effect of interaction between layers on the electrical transport was interpreted.

Keywords: Manganese perovskite, trilayered films, Interaction between layers

PACC: 7280G, 7360,7570P

HTS BANDSTOP FILTER WITH NOVEL STRUCTURE

AND HIGH SKIRT SELECTIVITY

SUN LIANG¹ CHEN JING^1,2 LI SHUN-ZHOU^1,3 HUANG JIAN-DONG¹

YIN ZHENG-CHAO¹ LI CHUN-GUANG¹ HE AI-SHENG¹ ZHANG XUE-QIANG¹ LI HONG¹

LUO SHENG¹ GU CHANG-ZHI² JIN AI-ZI¹ YANG HAI-FANG¹ FENG JI¹ HE YU-SHENG¹

^{1Institute of Physics, Chinese Academy of Sciences, Beijing 100080

^{2Department of Physics,University of Science and Tecnology, Beijing 100083

^{3Institute of Acoustics, Chinese Academy of Sciences, Beijing 100080

（Received 15 October,2003）}}}

A novel high-temperature superconducting bandstop filter is presented. The filter has been designed to have a center frequency of f₀≈2.5GHz and a maximal stopband attenuation of 65dB. The filter fabricated using double-side-coated YBCO thin film has a center frequency close to the designed value, and a maximal stopband attenuation of 73 dB, which is better than the specification and that of computer simulations in designing. The filter is not only with compact size, but also has high skirt selectivity, and can be easily integrated with other HTS devises in a single chip.

Keywords: HTS, microwave applications, bandstop filter

PACC: 7470V, 7870G, 4280C

Enhancement of Low-field Magnetoresistance

in La_0.67Ca_0.33MnO₃/Cu Composites

TANG JIE LIU SHENG ZHANG GUO-HONG ZHANG LI-JIANG YUAN SONG-LIU

Department of Physics Huazhong University of Science and Technology, Wuhan 430074

（Received 21 October,2003）

The influence of Cu contents on the electrical transport properties(resistivity) of a series of composite samples of La_0.67Ca_0.33MnO₃/Cu is studied. Results show that the Cu phase causes the low-field magnetoresistance, and dramatically reduces the resistivity. We suggest that the results are caused by a phase related to Cu at grain boundaries or surfaces of the La_0.67Ca_0.33MnO₃ grains.

Keywords: manganites, composite, grain boundary，magnetoresistance

PACC: 6848,7350V, 8160H, 7280T