Vol. 52, No. 10 (2003)
2003-05-20
GENERAL
2003, 52 (10): 2359-2362.
doi: 10.7498/aps.52.2359
Abstract +
Hirota bilinear method is a very effective method for solving nonlinear evolution equations. In this paper, by further generalizing this method, we obtain novel multi-soliton solutions of (2+1)-dimensional breaking soliton equation.
2003, 52 (10): 2363-2367.
doi: 10.7498/aps.52.2363
Abstract +
In this paper, we present a general approach to the construction of conservation laws for nonlinear non-holonomic dynamical systems by finding corresponding int egrating factors. The definition of integrating factors for the Routh equations of non-holonomic systems is given, and the necessary conditions for the existenc e of conserved quantities of the non-holonomic dynamical systems are studied in detail. The conservation theorem and its inverse for the systems are established , and an example is given to illustrate the application of the results.
2003, 52 (10): 2368-2372.
doi: 10.7498/aps.52.2368
Abstract +
This paper studies the exact invariants and the adiabatic invariants for systems of generalized classical mechanics in the high-dimensional extended phase space and gives the relations between the invariants and the symmetries of the system s in the space. Based on the concept of high-order adiabatic invariant of mechan ical systems with the action of small disturbance, it presents the form of the h igh-order adiabatic invariant and the conditions for their existence,and establi shes the relationship between adiabatic invariant and symmetrical transformation . In the end of this paper, an example is given to illustrate the application of the results.
2003, 52 (10): 2373-2378.
doi: 10.7498/aps.52.2373
Abstract +
In this paper, we obtained five kinds of new doubly-periodic solutions by using sinh-Gordon equation expansion method for nonlinear coupled scalar field equations which show physical significance and application value. In degeneration, we can obtain the new solitary wave solutions and trigonometric function solutions. The results showed that the equation has plenty of constructions of solutions, the physical phenomena of the physical model which the equation described, will be the object many physicists and mathematicians further explore.
2003, 52 (10): 2379-2385.
doi: 10.7498/aps.52.2379
Abstract +
Based on an ordinary differential equation which possesses doubly-periodic solut ions, a new method for constructing doubly-periodic solutions for differential e quations and its algorithm are proposed. This method can be carried out in compu ter by the aid of symbolic computation. A lot of new exact solutions of the nonl inear coupled scalar field equations are found by using this method.
2003, 52 (10): 2386-2392.
doi: 10.7498/aps.52.2386
Abstract +
The propagation properties of evanescent waves in a multi-layered structure containing materials with negative refractive index are analyzed. The decay or magnification of the amplitude of evanescent waves in different situations is explained analytically in detail. In particular, the influence of the dissipation of the negative refractive index medium on the photon tunneling effect is discussed. The propagation and energy storage of evanescent waves are shown clearly by using the incidence of a Gauss beam.
2003, 52 (10): 2393-2398.
doi: 10.7498/aps.52.2393
Abstract +
We mainly consider the case that one of the two entangled atoms with two energy levels interacts with a single-mode and double-photon cavity field. The atom is selectively detected after exiting the cavity, and it is found that the noncla ssical properties of field states depend strongly on the entanglement degree bet ween the two atoms. Meanwhile, it is proved that the squeezing of the field and the photon antibunching can be greatly enhanced via selective atomic measurement s.
2003, 52 (10): 2399-2403.
doi: 10.7498/aps.52.2399
Abstract +
The finite size effect in the Eguiluz-Zimmermann (EZ) model is studied. It is found that the finite size effect is very important if the number of the agents N is large enough and the probability of trading among the agents is small enough :a1/N. In this case, the model becomes almost a big single cluster system that includes almost all the agents. For the small clusters, the size distribution c an still satisfy a power law. However, the exponent will change due to the fluct uation effect. For a1/N, it can be proved that the fluctuation effect is not i mportant, hence the mean field theory is correct.
2003, 52 (10): 2404-2408.
doi: 10.7498/aps.52.2404
Abstract +
There are many reports on extracting the single frequency signal under noise by the stochastic resonance, but in which the information that the signal carries is zero. The experimental investigation in this paper manifests, when it is driven by an amplitude modulation wave and white noise, not only that the output of nonlinear bistable system exhibits the stochastic resonance phenomenon, but also that the modulation signal (information signal) can be extracted from the output by detecting and filtering. As compared with that from the electronics system by detecting and filtering direct the signal-to-noise(SNR) of modulation signal f rom the nonlinear bistable system is higher. Under the condition of adiabatic ap proximation the analytical formulation of the SNR of modulation signal is provid ed.
2003, 52 (10): 2409-2414.
doi: 10.7498/aps.52.2409
Abstract +
This paper studies mainly the dynamical behaviour of a cellular neural network. The dynamical property is controlled via adjusting the weight parameters of the system. The results indicate the structure of the attractor depends sensitively on the alteration of a parameter, and the dynamical behaviour of the cellular neural network shows the chaotic attractor with a larger extent of parameters.
2003, 52 (10): 2415-2420.
doi: 10.7498/aps.52.2415
Abstract +
The chaos control methodology based on the washout filter technology is used in chaotic systems both without perturbation and with perturbed parameters. A sufficient condition on controller design with perturbed parameters is presented. Numerical results show that this method is easy to be implemented in engineering, requires little control cost, stabilizes the original unstable fixed points within the chaotic attractor and is robust enough. Thus, it is very suitable for engineering applications.
2003, 52 (10): 2421-2426.
doi: 10.7498/aps.52.2421
Abstract +
For the improved Nagel-Schreckenberg model, we study it with an open boundary c ondition. We analyze the influence of the boundary condition,safety distance and deceleration probability on the traffic flow.
2003, 52 (10): 2427-2431.
doi: 10.7498/aps.52.2427
Abstract +
In this paper we analyze the variation in the chemical potential of the liquid d roplets at the critical state and the condensation that follows, and discuss the mechanism of mixed condensation. It is proved that there is a possibility of re alizing dropwise condensation with small contact angle when the super cooling of the condenser surface reduces and the dropoff radius of the droplet on the surf ace reaches a small value through certain appropriate methods.
2003, 52 (10): 2432-2437.
doi: 10.7498/aps.52.2432
Abstract +
A new technique, twice sampling stochastic resonance (SR), is proposed, and with this technique, the goal of detecting a weak signal overwhelmed in a noise is r ealized under large parameters in terms of the theory of adiabatic elimination. For the purpose of practical applications, the relative parameters are investiga ted in the detection of a weak signal based on the technique. The numerical simu lation shows that the method presented here is of potential value in the signal analysis and is expected to be applied to the practically measured data processi ng in the future.
ATOMIC AND MOLECULAR PHYSICS
2003, 52 (10): 2438-2442.
doi: 10.7498/aps.52.2438
Abstract +
The structures of LiH, LiO and LiOH have been optimized based on the density functional (B3LYP/sdd) method with relativistic effective core potential. The Murrell-Sorbie analytic potential energy functions for LiH and LiO, and the many-body expansion analytic potential energy function for LiOH are derived by using the many-body expansion theory and normal equation fitting methods. The dissociation energies for LiH, LiO and LiOH are calculated from the analytic potential energy functions. Then, the atomic and molecular reaction dynamic processes for the collision of O+LiH(ν=0,j=0) system are investigated with the present potential energy functions by Monte-Carlo quasi-classical trajectory approach. The results show that O+LiH(ν=0,j=0) has no energy threshold, and the dominated product is LiO.
2003, 52 (10): 2443-2448.
doi: 10.7498/aps.52.2443
Abstract +
The enhancement of stimulated Raman scattering (SRS) of weak-gain Raman modes is demonstrated by overlapping the Stokes wavelengths of the Raman modes with Dye lasing gain. Four SRS spectral lines related to C-H stretching modes of ethanol in a～10-5mol/L Rhodamine 640-doped ethanol pendant drop can be ob served, which are supported by the lasing gain of Rhodamine 640. The dye lasing is found to be partially and even totally suppressed by the intense SRS of ethanol as the pump intensity increasing from 1.2×108W/cm2 to 3. 3×108W/cm2.
2003, 52 (10): 2449-2452.
doi: 10.7498/aps.52.2449
Abstract +
A simple model is proposed to study the ionization of the atomic hydrogen by fast election impact in coplanar asymmetric geometry, making use of the post form of the enery shell transition matrix element and the two-potential formula. By virtue of dividing the full kinetic energy operator, we obtain an approximate solution of the three body problem through the canceling of the motion of two-election mass and exponent factor of relative motion and the approximation of projectile plane wave. TDCS(triple differential cross section) is expressed by the product of two factors,the structure factor T2 and correlation one T12. In this article, the contribution of these factors is investigated using the method of asymptotic series and method.
2003, 52 (10): 2453-2456.
doi: 10.7498/aps.52.2453
Abstract +
Soft x-ray emission from Ar clusters irradiated by intense 150 fs laser pulses a t an intensity of～5×1015 W/cm2 has been measured with a flat field spe ctrometer. Strong transitions from ArⅧ charge states have been observed, some s pectral lines belong to ArⅫ and ArⅩⅢ. Compared with optical field ionization, the interaction of intense laser pulse with clusters enhances drastically the a bsorption of laser energy and higher charge states are obtained as well. The sig nificant change in the spectrum is attributed to the collisinal heating of small -sized Ar clusters formed at on enough baking pressure of gas.
2003, 52 (10): 2457-2461.
doi: 10.7498/aps.52.2457
Abstract +
The study of radon release and migration is the basic theoretical issue for rado n measurement, which has a close relationship with extensive applications in geo science, environmental science and so on. In this paper, a new theory of migrati on of radon and its daughters has been discussed. The mechanism of vertical mig ration of radon and its daughters is: after α-particles emitted by radon and it s daughters decelerate, they become He nucleus. The He nuclei can combine with r adon and its daughters and form clusters. Because He is very light, it can make the specific gravity of the clusters lower than their buoyancy in the medium. As a result, the clusters will rise of their own accord. When the specific gravity of the clusters is higher than their buoyancy, the clusters will drop down. The theoretical distribution equation is established to describe radon migration an d proved by experiment as well.
CLASSICAL AREA OF PHENOMENOLOGY
2003, 52 (10): 2462-2465.
doi: 10.7498/aps.52.2462
Abstract +
We propose a kinoform-based iterative random phase encryption method, in which t he phase retrieval algorithm is divided into two steps: 1) random phase encrypti on and 2) iteration solving for phase distributions of both the key phase plate and the kinoform. Since the iterations are executed between a Fourier spectrum a nd the kinoform, the decryption errors can be effectively depressed. By the quan tization process for the phase distributions during the iterations, a method of increasing the abundance of design is used to depress the decryption errors. The simulation results are presented at the end, which agree well with the theoreti cal analysis.
2003, 52 (10): 2466-2470.
doi: 10.7498/aps.52.2466
Abstract +
We study the micromaser in a two-mode quantized cavity field injected with a two -level atom. A solution in the dressed state description is presented for the sy stem. We investigate,under the thermal-atom regime, the influence of detuning Δ on the atomic emission probability, when the two-mode quantized cavity field is prepared in different states.
2003, 52 (10): 2471-2475.
doi: 10.7498/aps.52.2471
Abstract +
Influence of energy-transfer upconversion (ETU) effect on the output pulse in diode-pumped Cr:YAG passively Q-switched lasers is investigated. Using the ETU theory and Q-switching rate equations, the initial population inversion, the final population inversion and the threshold population inversion at the maximum photon density are achieved. The output pulse width and pulse energy depend on the relation between them. The predicted results are in good agreement with the experimental results. The method of reducing the ETU effect is also discussed and it is useful to optimize this kind of lasers.
2003, 52 (10): 2476-2480.
doi: 10.7498/aps.52.2476
Abstract +
The parameters of 1.34μm Nd:YVO4 flat-concave cavity laser with an end-pumped mode are theoretically analyzed.The operation of 1.34μm Nd:YVO4 flat-concave cavity laser end-pumped by a diode-laser is achieved.
2003, 52 (10): 2481-2485.
doi: 10.7498/aps.52.2481
Abstract +
This paper discusses the characteristics of phase-only modulation using a reflec tive liquid crystal on silicon(LCOS). The 2×2 Jones matrix method is used as a computational tool to theoretically analyze phase modulation characteristics. Th e system has been constructed for testing of amplitude and phase, in which a He- Ne laser as the light source, testing the wave front phase using an interferomet er. The LCOS displays as a liquid crystal spatial light modulator and its drivin g circuit is controlled by a computer, digital data are sampled by CCD. We have tested the phase modulation of 1024×768 LCOS displays. Given the state of input and output polarizations ,the result of testing our theories by experiment sho w consistency ,so LCOS displays can be used as phase-only modulator.
2003, 52 (10): 2486-2491.
doi: 10.7498/aps.52.2486
Abstract +
Microcrystalline phases were produced by laser irradiation on the Fe73.5Cu1Nb3Si13.5B9 amorphous ribbon with a power ranging from 40 to 170W,scaning speed 10mm/s,laser beam spot 20mm. Hyperfine structures of the original and crystallized samples were analyzed by transmission Mssbauer spectros copy. We discovered that the basic parameters of the Mssbauer spectra——isome r shift（IS）, quadrupole splitting（QS） and hyperfine magnetic field（Hhf） ch ange with the laser power. Experimental results show that the magnetic moment re organization of Fe73.5Cu1Nb3Si13.5 B9 amorphous phases has take n place and the atom magnetic moment direction maintains a preferred in-plane or ientation, The average hyperfine magnetic field of the amorphous phase is improv ed because of the microcrystalline phase. The crystallized phase was Fe-Si alloy with a DO3 structure, and the area of its spectral lines is about 2% —3.4%. This is caused by the jump of one electron in Fe atom 3d6 shell int o Si atom 3p2 shell, forming a stability electron group.
2003, 52 (10): 2492-2499.
doi: 10.7498/aps.52.2492
Abstract +
In this paper, the spring model for the anisotropic interface layer is built and introduced to the global matrix technique that is popularly used for analyzing layered composites. In introducing the spring interface condition, the philosophy adopted is to incorporate it with a minimum disruption to the program structur e, particularly the assembly of the global matrix. The spring interface has ther efore been introduced as a "material layer". This layer has material constants w hich govern the stiffness across it and has zero thickness. The layer can be bui lt into the appropriate location in the global matrix without making any changes in the other layers of the system. Numerical computations for the Lamb wave dis persion curves in two-layered anisotropic composite media with different interfa ce conditions including rigid connection, slip connection, and complete disbond are made，and plots of the through-thickness particle displacement distributions of Lamb modes for the rigid bond interface and slip bond interface are compared .
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
2003, 52 (10): 2500-2507.
doi: 10.7498/aps.52.2500
Abstract +
Starting from kinetic equations,we discussed stimulated Raman scattering(SRS)by including both Landau damping(LD) and the collisional damping(CD).It was found that the linear growth rate of SRS is reduced substantially due to LD and CD.SRS can occur only for a region determined by both electron temperature and density .Gap in the spectrum corresponding to Raman scattering can be explained by the p resent model.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
2003, 52 (10): 2508-2513.
doi: 10.7498/aps.52.2508
Abstract +
After the Gd3(Fe1-xCox)29-yCry compound was formed, Sm3(Fe1-xCox)29 -yCry compounds were also successfully fabricated. Phase stability of R3(Fe1-xCox)29-yCr y(R=Gd,Sm) compounds was invest igated by x-ray diffraction and magnetic measurements. Atomic radius theory was employed to interpret why the 3∶29 compounds with high Co component had to cont ain more stabilizing elements. Less stabilizing elements are needed for those wi th larger atomic radius. However,a large atom of a stabilizing element augments the lattice parameter of the compound, which is disadvantageous to the stability of the 3∶29 phase. By studying the phase stability of R3(Fe1-x Cox)29-yCry(R=Gd,Sm) compounds, we have fabricated the Gd3(Fe1-xCox )29-yCry(0.4≤x≤1.0; 4.0≤y≤6.5) and Sm3(Fe1-xCox)29-y Cry(0.4≤x≤1.0; 4.5≤y≤7.5)compounds with room-temperature uniaxial magnetocrystalline anisotropy.
2003, 52 (10): 2514-2519.
doi: 10.7498/aps.52.2514
Abstract +
A Moiré technique using a scanning probe microscope (SPM) is developed, in which the natural periodic structure of a crystal is used as an ideal spacing grating. Formation principle of the SPM moiré fringes is discussed. Moiré patterns formed on highly oriented pyrolytic graphite (HOPG) and mica are investigated experimentally with STM and AFM, respectively. The results demonstrate the feasibility of the SPM Moiré technique in studying deformation and defects of crystals at the nanometer scale.
2003, 52 (10): 2520-2524.
doi: 10.7498/aps.52.2520
Abstract +
In this paper, molecular dynamics simulations are used to study the structure of Ni-based single superalloys with a {100} Ni/Ni3Al grain boundary. Tw o differe nt initial models are relaxed at 300K using Finnis-Sinclair-type potential. Our simulations reveal that the misfit energy due to the difference of their lattice constants is released not by long-range lattice misfit but by forming dislocati ons in local regions. Due to the surrounding differences of Ni3Al pha se in Ni-based phase, the dislocations formed are different.
2003, 52 (10): 2525-2529.
doi: 10.7498/aps.52.2525
Abstract +
We report the photo-induced crystallization behaviour of Au+-doped silicate glasses fabricated by Ti: sapphire femtosecond pulsed laser and successive heat treatment. Absorption spectra showed gold nanoparticles precipitated near the f ocal point of the laser beam. We also demonstrate that the size distribution of nanoparticles can be controlled by the laser irradiation conditions. Gold nanop articles-doped glasses reveal stronger optical limiting effects for nano-second laser pulses, and optical nonlinearities of the composite glass were also affec ted by laser irradiation conditions.
2003, 52 (10): 2530-2533.
doi: 10.7498/aps.52.2530
Abstract +
The depth-concentration distribution in dry peanut seeds for implanted V+ at 2 00keV was measured by two-photon laser scanning microscope. It was observed that when the ions were implanted into peanut samples along longitudinal direction a nd transverse direction, the corresponding depth-concentration distribution curv es possess different shapes and characteristics. This is called directional effe ct. The origin of this directional effect was studied primarily.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
2003, 52 (10): 2534-2540.
doi: 10.7498/aps.52.2534
Abstract +
With a brief discussion of the physical mechanism of spectroscopic derivative, the successful applications are given in optical absorption and reflectivity study of GaxIn1-xAs/InP and GaxIn1-xP/Al GaInP multiple quantum wells . The effects of different orders of the derivative are compared with each other , and the difference is pointed out between this method and the curve-fitting me thod as well as the double modulation method. A conclusion is reached that the m ethod is practical and reliable in the optical study of wide band-gap quantum we lls.
2003, 52 (10): 2541-2546.
doi: 10.7498/aps.52.2541
Abstract +
Based on the material data of 4H-SiC, we present a breakdown model for 4H-SiC pn junction diode, which includes both the avalanche impact ionization and the ban d-to-band tunneling. With this model, the influence of tunneling on the breakdow n characteristics of the devices is analyzed. The breakdown mechanism at differe nt temperatures and doping concentrations is explained, and the simulation resul ts can give a nice description for the breakdown characteristics of real devices .
2003, 52 (10): 2547-2552.
doi: 10.7498/aps.52.2547
Abstract +
We investigate theoretically the dynamic process of polarons and bipolarons in n ondegenerate polymers. In a low field, it is bigger that the carriers are charge d polarons or bipolarons，their lattice configurations and charge densities move together all along. The velocity of polarons is bigger than that of bipolarons in the same system. Both polarons and bipolarons have their saturated velocities .The saturated velocities decrease with the increase of the nondegenerate parame ters. In a high electric field, the electronic states of polarons and bipolaron s are dissociated from their lattice states, and move with high velocities. In t his case, the carriers are electrons rather than polarons or bipolarons.
2003, 52 (10): 2553-2557.
doi: 10.7498/aps.52.2553
Abstract +
A novel SiC metal-oxide-semiconductor field-effect transistor (SiC SBSD-MOSFET) with Schottky barrier contacts for source and drain is presented in this paper. This kind the device gives a fabrication advantage of avoiding the steps of ion implantation and annealing at high temperatures of the conventional SiC MOSFET. Also It has no problems of crystal damage caused by ion implantation and low activation rate of implanted atoms. The operational mechanism of this device is analyzed and its characteristics are comparable to the conventional SiC MOSFET from the simulation with MEDICI. The effects of different metal workfunctions, oxide thickness, and gate length on the device performance are discussed.
2003, 52 (10): 2558-2562.
doi: 10.7498/aps.52.2558
Abstract +
The Raman back scattering/channeling technique was used to analyze the damage recovery at different annealing temperatures and to determine the lattice locatio n of the Er-implanted GaN samples. A better damage recovery was observed with in creasing annealing temperature below 1000℃, but a complete recovery of the impl antation damage cannot be achieved. For a sample annealed for at 900℃ 30 min th e Er and Ga angular scans across the axis was measured, indicating that a bout 76% of Er ions occupies substitutional sites. Moreover, the photoluminscenc e (PL) properties of Er-implanted GaN thin films have been also studied. The exp erimental results indicate that those samples annealed at a higher temperature b elow 1000℃ had a stronger 1539nm PL intensity. The thermal quenching of PL inte nsity for samples annealed at 900℃ measured at temperatures from 15K to 300K is 30%.
2003, 52 (10): 2563-2568.
doi: 10.7498/aps.52.2563
Abstract +
We have designed a novel three-valued single-electron memory.This memory compris es two multiple-tunnel junctions(MTJs) and a single-electron transistor which ac ts as an electrometer.Because the Coulomb gaps of the two multiple-tunnel juncti ons are different,the device have three stable states.It is possible to fabricat e multiple-valued single-electron dynamic random access memories(DRAM)and nonvol atile random access memories(NOVORAM).The memory,which is promising for high fre quency and low power-dissipation,can achieve ultradense data storage.
2003, 52 (10): 2569-2575.
doi: 10.7498/aps.52.2569
Abstract +
We investigated spin-polarized transport properties for electrons tunneling through a few of magnetic-electric barrier structures.The general formula of the transmission was derived.The relationship between the spin-polarization and the distribution of the nonhomogeneous magnetic field was revealed.Furthermore,our results also indicated that the spin-filtering effect can be enhanced significantly when a semiconductor with a larger g factor is used.
2003, 52 (10): 2576-2579.
doi: 10.7498/aps.52.2576
Abstract +
This paper analyzes the degradation in GaAs pseudomorphic high electron mobitity transistors (PHEMT's) by measuring the electric characteristics in GaAs PHEMT's before and after stress. The relation between impact ionization rate and maximu m channel electric field is gained. An analytical expression of impact ionizatio n rate versus maximum channel electric field is deduced by fitting the experimen tal results. The electric characteristic and reliability in GaAs PHEMT's can be improved and evaluated using the analytical expression. The impact ionization in channel should be decreased in order to improve the breakdown voltage in GaAs P HEMT's.
2003, 52 (10): 2580-2583.
doi: 10.7498/aps.52.2580
Abstract +
We have designed and fabricated a new type of highTc rf SQUID sensor. A high T c coplanar superconducting resonator and a large area high Tc superconductin g film concentrator have been used simultaneously. With a large effective area and low white flux noise, we have achieved a flux noise of 2.1×10-5 0 /Hz and a magnetic field sensitivity of 34fT/Hz in white noise range, respective ly, using an effective area of 1.27 mm2 concentrator on a 15 mm×15 m m substra te. This design can be easily applied to higher frequency high Tc rf SQUID system.
2003, 52 (10): 2584-2588.
doi: 10.7498/aps.52.2584
Abstract +
We used the first equation of Ginzburg_Landau theory to study superconductivity with no magnetic field considered. We have obtained the effective mass m of Ginz burg_Landau equations, which has a special property, namely it can be negative. Some explicit expressions for different cases are derived, which are consistent with experimental data.
2003, 52 (10): 2589-2595.
doi: 10.7498/aps.52.2589
Abstract +
Using Bogoliubov_de Gennes equations,we obtain the self_consistent equation in a ferromagnetic superconductor. Taking into account the rough interface scatterin g effects, within Bogoliubov_de Gennes equations and Furusaki_Tsukada formula we calculate the dc Josephson current in the double ferromagnet_superconductor tun nel junctions. It is found that dc Josephson currents in FS/I/FS are suppressed by the ferromagnetic exchange interaction for weak barrier strength and weak rou gh interface scattering strength. The only exception that the dc Josephson curre nts increase with the ferromagnetic exchange interaction occurs if all three con ditions are satisfied: at low temperature, for strong barrier strength or strong rough interface scattering strength, and in an antiparallel configuration.
2003, 52 (10): 2596-2600.
doi: 10.7498/aps.52.2596
Abstract +
Sr_Ru cuprates synthesized via traditional solid_state reaction is always accompanied by the formation of small amounts of SrRuO3 impurity phase with ferromagnetism. In this paper we report that not only the pure phase compound Sr2 GdR uO6 without any ferromagnetic SrRuO3 impurity phase is suc cessfully prepared by means of a new_type reaction of solid state in presence of O2 (or air)_wat er vapor mixed atmosphere，but also RuSr2(Gd,Ce)2Cu2O10(Ru_1222）wit hout any ferromagnetic SrRuO3 impurity phase is further synthesized u nder a re lative low reactive temperature when the Sr2GdRuO6 is used as a precursor. T he authors discuss the formation of the product Sr2GdRuO6 and mechanism of t he new_type reaction of solid state in presence of water vapor in detail. In add ition, the effects of SrRuO3 impurity phase on the electric propertie s of the product Ru Sr2(Gd,Ce)2Cu2O10 is also discussed. It suggests that the water vapor for the new_type solid_state reaction is not beneficial to the tran sformation of SrRuO3 to Sr2GdRuO6, and it is to suppress the formation of SrRuO3 due to the formation of RuO2·nH2O. Thus the amount of SrRuO3 impurity phase in Ru_1222 phase is controlled in the reaction of solid state. I t seems that the presence of a small amount of SrRuO3 impurity phase is favourable for making the Ru_1222 phase superconductive.
2003, 52 (10): 2601-2606.
doi: 10.7498/aps.52.2601
Abstract +
Reflection high-energy electron diffraction (RHEED) is very surface sensitive and often used for the analysis and monitoring of thin film growth in ultrahigh vacuum deposition system (for instance, Molecular Beam Epitasis). In order to in-situ monitor the growth of oxide thin films at high oxygen pressure up to 50Pa, a high-pressure RHEED designed and fabricated by our group was used for first time in our pulsed laser deposition system (PLD). Using the PLD system the Nb-doped SrTiO3 (STNO) and Y1Ba2Cu3O7 (YBCO) thin films have been epitaxially grown on SrTiO3 (001) substrates. T he RHEED patterns of the STNO and YBCO films and the oscillation of the intensity of the pattern have been measured by the high-pressure RHEED during deposition. In addition,the surface morpholoyg of the films and the dynamic analysis of film growth process were discussed.
2003, 52 (10): 2607-2611.
doi: 10.7498/aps.52.2607
Abstract +
The thermodynamical properties of quantum Heisenberg films are studied in variat ional cumulant expansion. The spontaneous magnetization，internal energy and spe cific heat are calculated to the third order. For a thicknesses below a critical value, the magnetization decreases rapidly as the number of atomic layers is de creased. The internal energy increases with decreasing number of atomic layers at any given temperature, and the specific heat increases below the critical tem perature and decreases beyond the critical temperature with decreasing number o f atomic layers.
2003, 52 (10): 2612-2615.
doi: 10.7498/aps.52.2612
Abstract +
The structure and Curie temperature of Y2(Fe1-x-y,Coy ,Crx)17 c ompounds have been investigated by means of x_ray diffraction and magnetization measurement. The Y2(Fe1-x-y,Coy,Crx) 17 compounds have a hexago nal Th2Ni17_type structure. With increasing x, the unit_ce ll volumes of Y2Fe17-xCrx and Y2CoFe16-xCrx compounds have a small decreas e initially, followed by a greater decrease. It is proved that the magnetic inte raction of Fe atoms at 4f sites of Y2Fe17 compound is anti ferromagnetic by studying the variation of Curie temperature of Y2(Fe1-x-y,Coy,Crx )17 compounds. The result also shows that a few Co and Cr atoms subst ituti ng for Fe atoms can enhance Curie temperature of Y2(Fe1-x-y,Coy,Crx)17 obviously.
2003, 52 (10): 2616-2621.
doi: 10.7498/aps.52.2616
Abstract +
Co/Pd1-xMnx multilayers with Mn concentration x=0 to 20.8 % have been sp uttered on a glass substrate with 40 nm thick Pd or PdMn buffer. With the combin ation of small_ and large_angle x_ray analyes, the crystal structure of the samp les were investigated. Hysteresis loop and perpendicular magnetic anisotropy (PM A) were measured by means of an alternating_gradient magnetometer and magnetic t orque. Domain structure was observed by magnetic force microscopy. Saturation ma gnetization, PMA and the Kerr rotation spectrum of the samples were investigated . It is shown that the change of Kerr rotation with the increase of Mn concentr ation in Pd could be ascribed to the variation of diagonal and off_diagonal elem ents of the dielectric tensor.
2003, 52 (10): 2622-2626.
doi: 10.7498/aps.52.2622
Abstract +
We have carried out an experimental study based upon the ferromagnetic resonance (FMR) on the anisotropy of alloy ribbons of (Fe1-xCox)84Zr3.5Nb3.5B8Cu1(x=0.0, 0.2, 0.4, 0.6, 0.8). The easy axes of the samples are in the lateral direction of the ribbons, While the single-axis anisotropy c onstant K′ of the samples having the same width decreases as the amount of Co i ncreases. The value of K′ lies between 4.67×10-5J/m4(x=0 .0) and 2.54× 10-5J/m4(x=0.8). Since the imaginary part χ″ of the alte rnating curren t magnetic susceptibility changes nonlinearly with the magnetic field H, there is a low field (0—12 mT) non_resonance signal having a comparable strength wit h that of the ferromagnetic resonance signal. It is found through the study on t he magnetic process of the alloy ribbon of Fe84Zr3.5Nb3.5B8C u1 that dχ″/dH=0 in the regions of the reversible (0—12 mT) and saturated (9.0 mT—12 mT) magnetization that χ″(H) is related to the n_th power of H, i .e., Hn(n≥3) when the domain wall motion is nonreversible; and χ″ is relate d to H2 during the domain rotation (Rayleigh region, dχ″dH is a con stant). S pecifically, it is found that the χ″(H) proportional to H2 and tha t proportional to Hn(n≥3) appear alternatively in three sections, correspon ding to the disappearance of different domains.
2003, 52 (10): 2627-2631.
doi: 10.7498/aps.52.2627
Abstract +
Lanthanum_doped intergrowth ferroelectrics: (Bi,La)4Ti3O 12-Sr(Bi,La)4Ti4O15 (SrBi8-xLaxTi7O27) (x＝0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50) ceramic samples have been prepared by solid_state reaction m ethod. Their structure was analyzed by x_ray diffraction, and their dielectricit y and ferroelectricity were measured. It is found that La doping does not change the crystal structure of Bi4Ti3O12-SrBi4Ti4O15. The coerciv e field (EC) of SrBi8-xLaxTi7O2 7 increases slightly and the remnant polarization (2Pr) increases at first, then decreases with th e increas e of La content. The 2Pr reaches a maximum value of 25.6 μC·cm-2, whe n x is 0.50. The 2Pr increases nearly 60%, but the EC incr eases only about 10%, compared with those of SrBi8Ti7O27. Their temperatures of phase t ransition (TC) decrease with La doping. The TC of SrBi7.5La0.50Ti7O27 is 556 ℃ and shows good thermal stability. As x becomes 1.50, the SrBi7.5La0.50Ti7O27 exhibits a characteristic of relaxor ferroelectrics.
2003, 52 (10): 2632-2637.
doi: 10.7498/aps.52.2632
Abstract +
We have studied the growth and optical properties of AlInGaN alloys in this arti cle. By the measurement of three samples, we found that the incorporation of In decreases with the increase of temperature, while there is nearly no change for the incorporation of Al. The sample grown at the lowest temperature had the best material and optical properties, which owes to the high In component, because t he In component can reduce defects and improve the material quality. We also use d the time_resolved photoluminescence(PL) to study the mechanism of recombinatio n of carriers, and found that the time dependence of PL intensity was not in exp onential decay, but in stretched_exponential decay. Through the study of the cha racter of this decay, we come to the conclusion that the emission comes from the recombination of localized excitons. Once more, this localization exhibites the character of quantum dots, and the stretched_exponential decay results from the hopping of carriers between different localized states. In addition, we have u sed the relation of emission energy dependence of carrier's lifetime and the cha racter of radiative recombination and non_radiative combination to confirm our c onclusion.
2003, 52 (10): 2638-2641.
doi: 10.7498/aps.52.2638
Abstract +
The broadband yellow luminescence(BYL) of undoped GaN film is fitted optimally by the linear superposition of multiple Gaussian functions by using nonlinear optimization technique. It is found that the BYL may be divided into the three Gauss_type spectra. It shows for the first time that the BYL originates from the combination of three independent radiative transitions. The energy levels of the initial states of the three independent transitions are measured directly in experiment by means of a novel absorption_normalized photoluminescent excitation spectroscopy. It is found that the three independent transitions have the same initial state but different final states. The origins of the initial and final states are assigned reasonably.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
2003, 52 (10): 2642-2648.
doi: 10.7498/aps.52.2642
Abstract +
The influence of electromagnetic field with a low frequency on the microstructure and solute solubility of 7075 alloy produced by CREM process have been investigated. Evolution of the liquidus and solidus as well as the solidification interval are also measured. Meanwhile, the flow pattern and temperature field before and after the application of electromagnetic field is also given by numerical simulation. The forced solution mechanism of alloying agents of 7075 alloy under the effects of electromagnetic field is explained from such factors as solute equilibrium coefficient of distribution, solidification interval, flow pattern and temperature field in sump and microstructure.
