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Volume 10 Issue 3
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Original Articles
Exact Solution of the Bloch Equation with Time- Dependent Coefficients and Aharonov-Anandan Phase
XU Jingbo, WANG Lan, GAO Xiaochun
Chin. Phys. Lett. 1993, 10 (3): 129-131 .  
Abstract   PDF(pc) (140KB) ( 749 )
In this letter, the matrix invariant of the Bloch equation with time-dependent coefficients is found, the time evolution of the system is discussed and the exact solution of the system is obtained. We then proceed to study the cyclic evolution of the system, obtaining the Aharonov-Anandan phase Finally, it is shown that the study of noncyclic evolution of the system can be reduced to the cyclic evolution.

A TlBaCaCuO Thin Film Planar dc-Squid Magnetometer
CHEN Lie, ZHANG Lihua, WENG Yaojun, YANG Tao, LIU Dong, SHAO Kai, YAN Shaolin
Chin. Phys. Lett. 1993, 10 (3): 132-134 .  
Abstract   PDF(pc) (170KB) ( 444 )
A superconducting quantum interference device (squid) was made from TlBa-CaCuO(TBCCO) thin film. The squid loop forms a part of the pickup loop. The squid hole is a square of about 100x100μm. The pickup loop and the squid loop inductances are estimated to be 11 nH and 190pH, respectively. The best value of equivalent flux noise as measured in the flux locked loop mode is 4x10-4 Ф0 / Hz1/2 at dc-1 Hz. The corresponding sensitivity resolution at this frequency is 9pT/Hz1/2, about a factor 8 higher than the squid loop area.
Measurements of the 2P3/2 Vacancy State Alignment of Au Induced by Proton, Lithium and Boron Ion Impact
XIA Zonghuang, MA Hongji, ZHUANG Yongzhong, XIE Xiaohong, LIU Hongtao, LU Xiting
Chin. Phys. Lett. 1993, 10 (3): 135-138 .  
Abstract   PDF(pc) (178KB) ( 465 )
In this paper, the degree of alignment of 2P3/2 vacancy state in Au induced by proton, lithium and boron ion impact was measured using a Si(Li) detector. Also the projectile-energy dependence of the degree of alignment was investigated over the projectile energy range from 0.2 MeV/amu to 2.0MeV/amu. The de-alignment phenomenon was observed for small relative impact velocities.
Critical Size of a Crossover from Noncrystalline Icosahedra to Crystalline Cuboctahedra Structure for Copper Clusters
LIU Lei, ZHU Lei, CHEN Kaitai, LI Yufen
Chin. Phys. Lett. 1993, 10 (3): 139-142 .  
Abstract   PDF(pc) (256KB) ( 563 )
We present an estimation of a critical size of a crossover from icosahedral to bulk-like (cuboctahedral) structures for copper clusters by a semi-empirical calculation of cohesive energies for both icosahedral and cuboctahedral copper clusters. The results are consistent with available experimental observations.
Theoretical Studies of the C60 and Alkali Metal-Containing Complexes C60M
ZHANG Daren, WU Ji’an, KONG Jing, YAN Jimin
Chin. Phys. Lett. 1993, 10 (3): 143-146 .  
Abstract   PDF(pc) (229KB) ( 668 )
The electronic structures of C60 ahd C60 M (M=Li, Na, K , Rb and Cs) were calculated by using an atom superposition and electron delocalization molecular orbital method. The results indicate that s valence electron of the atom of alkali metal was completely transferred to 5T1u orbital of C60. The stabilization energy of the system results mainly from the electrostatic interaction between polarized C60 and alkali metal atom.
Studies on the Character of Wide Band Frequency Doubling in LiB3O5 Crystal
XIE Fali, MAO Hongwei, WU Baichang, CHEN Chuangtian
Chin. Phys. Lett. 1993, 10 (3): 147-150 .  
Abstract   PDF(pc) (196KB) ( 481 )
The angular acceptance and the spectral acceptance about the retracing point of phase-matching angles for type I second-harmonic generation in LiB3O5(LBO) crystal have been measured. The exact wavelength in retracing point is found to be 1.303μm, and the spectral acceptance bandwidth and angular acceptance width are about 115nm-cm and 11mrad-cm respectively. A possible application of LBO crystal in direct frequency doubling of femtosecond laser pulse has been predicted with theory.

Study of Optical Nonlinearity in Hydrogenated Amorphous Silicon Carbide Film
XU Jun, CHEN Kunji, HUANG Xinfan, FENG Duan, ZHANG Dakui*, LI Qun*, WANG Wenyao*, QIU Peihua*
Chin. Phys. Lett. 1993, 10 (3): 151-154 .  
Abstract   PDF(pc) (218KB) ( 453 )
Hydrogenated amorphous silicon carbide (a-Sicx:H) films were prepared by glow discharge technique with gas mixture of silane (SiH4) and methan (CH4). The room-temperature optical bistability was demonstrated in uncoated a-SiCx:H films at the excitation wavelength about 532nm. The switch-on intensity of device is about 0.8 MW/cm2 and the switching time is in the nanosecond scale. The physical origin of the optical nonlin5arity in these materials is also discussed.
Analysis and Simulation of Evolution Induced Catastrophe
BAI Yilong, XIA Mengfen, KE Fujiu, LU Chunsheng, LING Zhong
Chin. Phys. Lett. 1993, 10 (3): 155-158 .  
Abstract   PDF(pc) (256KB) ( 684 )
A model of evolution induced catastrophe (EIC) characterized by a nonlocal interaction is proposed. The general feature of the model is its two bias states: explosively catastrophic and globally stable, both consisting in a cascade of locally unstable states. A one-dimensional analysis reveals a transition region from globally stable to catastrophe. A two-dimensional simulation gives a thin fractal fracture profile similar to that observed and also a possible spectrum of fracture fractal. All these are different from percolation. Hence, the EIC model may represent a prototype of natural processes.

Solid C60: Pressure Induced Phase Transitions
WANG Jifang, WANG Lijun, CHEN Liangchen, CHEN Hong, WANG Ruju, ZHANG Zhiting, CHE Rongzheng, ZHOU Lei
Chin. Phys. Lett. 1993, 10 (3): 159-162 .  
Abstract   PDF(pc) (237KB) ( 572 )
Based on in situ high pressure x-ray diffraction with diamond anvil cell by using synchrotron radiation and pressure-quench x-ray measurement, phase transition of C60 under high pressured is studied. The maximum pressure used is 30GPa in quasi-hydrostatic case but 44GPa in nonhydrostatic case. At ambient pressure, C60 crystal is a fcc phase with lattice parameter a=14.2086Å. It transforms from fcc to a lower symmetry phase at pressure of 13.7GPa, and then transforms to an amorphous state under pressure up to 25-30 GPa. This amorphous state is metastable at normal condition. Finally, the experimental results are discussed.

Spectral Property and Stability of Color Centers in Alkali Halide Crystals Induced by He+ Ion Implantation at Room Temperature
GU Hongen, CHEN Zhifang, LI Zhijuan
Chin. Phys. Lett. 1993, 10 (3): 163-166 .  
Abstract   PDF(pc) (227KB) ( 521 )
Thin colored layers with high density defect centers could be produced on alkali halide crystals implanted by 300-400keV He+ ions at room temperature. Besides well known absorption bands, several new absorption bands and colloid absorption band are observed in the crystals, such as 520 and 842nm absorption bands in the implanted LiF crystals, 840nm absorption band in the implanted NaF :OH- crystals, and 875 nm absorption band in the implanted NaC1:OH- crystals.

Plasmon Excitation in 2D and 3D C60 Studied by Photoemission
XUN Kun, DENG Junzhuo, YAO Jun, LIU Fengqin, TAO Xiaoping, LÜ, Si hua, WANG Zuquan, WU Sicheng,
Chin. Phys. Lett. 1993, 10 (3): 167-170 .  
Abstract   PDF(pc) (230KB) ( 654 )
For near monolayer (ML) C60 condensed on Sn substrate, x-ray photoemission studies of Cls level reveal a feature centered about 22eV below the main peak. Analyses show that the feature is caused by the plasmon loss of the two dimensional C60 film. Bulk plasmon loss peak(~ 28 eV blow the main peak), which has been observed on thick C60 films, was not observed on the C60 films with coverage θ < 2 ML. It indicates that the 28eV energy loss feature is due to a bulk plasmon associated with the solid C60 but not a single C60 molecule.
Properties of MnBiTe and MnBiTeAl Magnetic Thin Films
LUO Chunping, KONG Lingchao*, WANG Yinjun
Chin. Phys. Lett. 1993, 10 (3): 171-174 .  
Abstract   PDF(pc) (224KB) ( 617 )
MnBiTe and MnBiTeAl thin films prepared by vacuum evaporation, then annealing can form NiAs crystal structure and possess strong perpendicular anisotropy along c axis. The entering of A1 atoms into MnBiTe results in the increase of Ku, Hc, k and a modulation of its Kerr spectra. It turns out that A1 doping into NiAs type structure can carry out benefits for magneto-optical recording medium.

Magnetic Hardening of Rapidly Quenched Co-M-Zr (M=B, Fe) Alloys
SHEN Baogen, YANG Linyuan, CAO Lei, GUO Huiqun
Chin. Phys. Lett. 1993, 10 (3): 175-178 .  
Abstract   PDF(pc) (214KB) ( 540 )
Effects of the quenching rate and annealing temperature on hard magnetic properties of rapidly quenched Co84-x Bx Zr16 and Co82-xFexZr18 alloys were studied. The B- or Fe-content dependence of room temperature coercivity Hc, remanence Br and maximum energy product (BH)max are obtained. The Hc is suggested to originate from the microstructure with the optimal grain size.
Magnetostriction of RFe11Ti and RFe10Cr2
LI Jingyuan, LI Qing an, YANG Fuming, LI Ruqi, FAN Xiaoli, ZMAO Xuegen, JIA Kechang
Chin. Phys. Lett. 1993, 10 (3): 179-182 .  
Abstract   PDF(pc) (173KB) ( 637 )
The magnetostriction of polycrystal RFe11Ti (R=Nd, Sm, Gd, Tb, Dy, Ho, Er and Y) and RFe10Cr2(R=Tb and Dy) compounds with ThMn12-typestructure have been investigated at 77K and room temperature in magnetic fields up to 20kOe. The values ofmagnetastriction λt = λ|| - λ in H=20kOe at 300K are 180 x10-6 for TbFe11Ti and 106x10-6 for Tb10Cr2. The magnetostrictions for compounds with R=Nd, Sm, Dy, Ho and Er are very small. The signs of λt for all these compounds are in agreement with that predicted by the singleion crystal field theory. All studied samples show a volume magnetostriction feature. Their forced magnetostrictions Δω/ΔH have a value which is close to that of YFe11Ti, 27 x 10-10/Oe. It reveals that the Fe sublattice is responsible for the volumc magnetostriction.

Low Temperature Phase Transition of an Orthorhombic Tungsten Bronze Ferroelectric Sr2-xCaxNaNb5O15
ZHONG Weilie, ZHANG Peilin, ZHAO Huansui, HAN Zhaozhong*, CHEN Huanchu*
Chin. Phys. Lett. 1993, 10 (3): 183-185 .  
Abstract   PDF(pc) (164KB) ( 553 )
The dielectric and pyroelectric properties of a new ferroelectric crystal with orthorhombic tungsten bronze structure Sr2-xCaxNaNb5O15 have been investigated in the temperature range of 300 to 10 K. Based on anomalies in the properties and by use of Curie's principle of symmetry, a ferroelectric-ferroelectric phase transition between mm2 and m is found to occur at about 75K. On cooling through the transition, the spontaneous polarization deviates by about two degrees from the two-fold axis [001] to[h0l] direction in the mirror plane.

An Extremely High Coercivity in Cu Doped Bi,Ga: DyIG Films for Magneto-optical Recording
ZHOU Yong, SHEN Defang*, GAN Fuxi
Chin. Phys. Lett. 1993, 10 (3): 186-188 .  
Abstract   PDF(pc) (166KB) ( 551 )
Bi, Ga : DyIG and Cu doped Bi, Ga : DyIG films on glass substrates have been prepared by the pyrolysis method, and their coercive force (Hc) and compensation temperature were measured. An extremely high Hc value of 13kOe at room temperature was obtained in Cu doped Bi, Ga : DyIG films.

Effect of Heat Treatment on Electrical and Optical Properties of Cd2SnO4 Films
PENG Dongliang, JIANG Shengrui, WANG Wanlu
Chin. Phys. Lett. 1993, 10 (3): 189-192 .  
Abstract   PDF(pc) (226KB) ( 613 )
Cd2SnO4 (CTO) films prepared by radio-frequency reactive sputtering from a Cd-Sn alloy target in Ar-O2 mixtures have been found to be a n-type degenerate semiconductor in which oxygen ,vacancies provide the donor states and free carrier concentration is up to 4.46x 1026 /m3. The films were annealed at temperature up to 500°C in stable Ar flow. Large Burstein shift has been observed in the visible transmission spectra. Photoluminescence spectrum measurement indicates the intrinsic optical gap of crystalline CTO is about 2.156eV. Analysis of electrical and optical data on CTO films before and after heat treatment leads to a calculated optical band gap in the range of 2.37-2.64eV and an effective mass 0.22-0.48 of the free electron mass.
17 articles