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1.
V. A. Krakovskii 《Russian Physics Journal》1999,42(4):411-415
In the present paper the dispersion properties of surface magnetostatic waves (SMSWs) propagating in a stratified structure,
ferrite film—high-temperature superconducting layer, have been investigated. The problem of SMSW propagation in an inhomogeneous
stratified medium has been solved and the dispersion equation has been obtained. In the solution of this problem, the granular
nature of the high-temperature superconducting (HTSC) medium and the exposure to a constant magnetization field have been
taken into account. Upon exposure to the constant magnetic field the HTSC film becomes an inhomogeneous anisotropic medium
with respect to a variable magnetic field. The nonhomogeneous wave equation describing the SMSW field in a granular HTSC medium
has been solved by the method of sequential iterations. Corrections for the SMSW velocity and attenuation, calculated with
the use of the exact dispersion equation, are significant in comparison with previously obtained approximate values and exceed
20 and 40%, respectively. The method of analyzing electromagnetic fields in inhomogeneous granular high-temperature media
can be used to solve some other problems, where spatially inhomogeneous HTSC media are used.
Tomsk State University of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika,
No. 4, pp. 45–48, April, 1999. 相似文献
2.
M. V. Kozintseva A. M. Bishaev A. A. Bush M. B. Gavrikov K. E. Kamentsev N. A. Nizhel’skii V. V. Savel’ev A. S. Sigov 《Technical Physics》2017,62(6):890-894
The properties of short-circuited multiturn superconducting coils have been studied; coils with nonsuperconducting contacts have been fabricated from a high-temperature superconducting (HTSC) tape made by Super Power Company. The magnetic flux captured by HTSC coils has been measured at different values of magnetic field of the magnetizing solenoid. the critical current in the coils have been experimentally determined based on the maximum values of the field they captured. It is ~50% of the nominal value for this HTSC tape. The range of external magnetic field, where HTSC coils keep the captured magnetic flux, has been experimentally found. The obtained results have demonstrated the possibility of designing magnet systems with levitating coils made of HTSC tape, in which levitation is controlled without using feedbacks. 相似文献
3.
V. A. Krakovskii 《Russian Physics Journal》1998,41(7):700-704
The reflection of a magnetostatic surface wave from a strip of a granular high-temperature superconductor is investigated.
An expression obtained by the method of perturbations describes the field of the scattered wave. The coefficient of reflection
of the MSSW from the HTSC strip is calculated as a function of frequency and temperature. It is shown that the reflectance
is very low at temperatures above critical and that the HTSC ceramic behaves as an ordinary superconductor. The reflectance
rises sharply when the temperature drops below critical. As the critical current decreases, the reflectance drops off and
the film loses the high-temperature properties. An expression is derived for the loss resistance of the MSSW in a granular
HTSC film. The loss resistance amounts to a few kiloohms and falls off sharply as the film transitions to the superconductive
state. The results can also be developed for periodic HTSC structures and used in the design of frequency-selective devices,
as well as high-speed bolometric photodetectors.
Tomsk State University of Control Systems and Electronics. Translated Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No.
7, pp. 97–102, July, 1998. 相似文献
4.
A.N. Lykov M. Chiba Yu.V. Vishnyakov 《Journal of Physics and Chemistry of Solids》2008,69(12):3125-3128
The effect of enhancement of nonlinear properties of superconducting films is found in low-frequency magnetic field. Harmonic mixing of the electromagnetic radiation is detected. These results provide an argument in support of a new approach to design the active superconducting elements. A low-frequency oscillating magnetic field directed perpendicularly to the film surface forms an unstable vortex structure in the film. The frequency multiplication is intensified in the vortex unstable state. A transition of the vortex structure into the ground state synchronized by an external resonant circuit causes the generation of the electromagnetic radiation. Main advantage of these oscillators over Josephson junctions is high power emitted into a broadband system. 相似文献
5.
B. J. Yuan 《Zeitschrift für Physik B Condensed Matter》1994,96(2):165-178
Presented in this paper is a theoretical analysis of a planar surface induced mixed state for a superconducting film in parallel applied field. An analytical solution of the internal magnetic field is obtained based on Saint-James and de Gennes' order parameter in a film. An expression of Gibbs free energy per unit volume without restriction of a geometry is derived from non-linear Ginzburg-Landau (GL) equation in terms of a renormalized GL parameter and a modified geometric factor. Based on the Gibbs free energy, a phase diagram of distinguishing a first and second order phase transition for a type I superconducting film is calculated. The numerical results for exact solutions of spatial variation of order parameter, current density and internal magnetic field in the film geometry in parallel applied field case are presented. Near the upper critical field, the first entry of an applied field in the film exhibits a laminar structure. 相似文献
6.
A Kosterlitz-Thouless-like transition in granular superconducting films is considered. A magnetic field fluctuations influence on thermodynamic properties is analyzed. A renormalization of an interaction constant because of “spin-wave” fluctuations is calculated. A role of a weak disorder is considered. A relationship between the transition temperature and the film sheet resistance is found to be in good agreement with experimental data. If the transition temperature is not too low the results are applicable to uniform superconducting films. 相似文献
7.
Propagation of magnetostatic waves (MSW) in planar magnetic structures with time-dependent parameters is studied theoretically and experimentally for the case where the structure is based on ferrite films. The time-dependent parameter is chosen to be the magnetizing field, which is taken to be uniform in space and slowly varying in time. Asymptotic perturbation theory is used to obtain an equation for the slowly varying amplitude and a relation for the phase, which describes the time behavior of the frequency and envelope of an MSW pulse. The time behavior of the frequency spectrum of an MSW propagating in an iron-yttrium garnet film is studied experimentally for different forms of modulation of the magnetic field. Space-time focusing of MSW pulses is studied for the case of a time-dependent field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 54–66, November, 1988. 相似文献
8.
The electrodynamic properties of granular high-temperature superconducting media are studied. Relations for the surface resistance and impedance of a high-temperature superconducting medium are derived. The temperature and frequency dependence of the phase velocity and group velocity and depth of penetration of the electromagnetic field into the Josephson medium are calculated. The possibility of using high-temperature superconducting films as high-efficiency shields is shown. The shielding properties are improved appreciably with increase in the critical current density of the high-temperature superconducting film. The shield thickness is several microns or several fractions of a micron for a critical current density of >107 A/m2. The results obtained can be used in designing superhigh-frequency shields, microstrip lines, and other devices based on high-temperature superconducting Josephson media. 相似文献
9.
We present a detailed study of the dispersion properties of surface magnetostatic waves in layered structures of ferrite and high temperature superconductor (HTSC) layers. We solve the propagation problem for the surface magnetostatic waves under a quasistatic approximation, and obtain the dispersion relation. We present an analysis of this dispersion near the phase transition temperature in the HTSC layer. The calculations show that when the HTSC material transforms to the superconducting state the dispersion properties of the magnetostatic waves changes suddenly: the damping decreases by 4–10 dB and the phase velocity increases by a factor of 2–4. These results support experiments which have been performed, in which surface magnetostatic waves have been studied in a YIG film with gallium impurities and a YBaCuO film on a lithium niobate substrate.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 50–55, March, 1995. 相似文献
10.
The effect of short-term low-temperature annealing in air and in vacuum on the properties of HTSC films of YBCO is studied. It is shown that, under certain conditions of preparation of initial samples, a transition from the HTSC phase with the superconducting transition temperature Tc=90 K to a phase with Tc=60 K occurs without a noticeable change in the oxygen content. It is found that, as a result of short-term annealings, a transition from the HTSC phase with Tc=60 K to the phase with Tc=90 K can occur only through the vacuum annealing stage, which converts the sample into the superconducting state. Short-term annealings lead to multiple reversible “switching” of the films from one phase to another. The obtained results are of practical interest, since the proposed method can be used to quickly obtain superconducting YBCO films in various phase states. It is shown, in addition, that the annealing procedure makes it possible not only to increase the oxygen concentration but also to produce a structural rearrangement of a YBCO film. 相似文献
11.
A new model analysis of the third harmonic voltage in inductive measurement for critical current density of superconducting films
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The critical current density J c is one of the most important parameters of high temperature superconducting films in superconducting applications,such as superconducting filter and superconducting Josephson devices.This paper presents a new model to describe inhomogeneous current distribution throughout the thickness of superconducting films applying magnetic field by solving the differential equation derived from Maxwell equation and the second London equation.Using this model,it accurately calculates the inductive third-harmonic voltage when the film applying magnetic field with the inductive measurement for J c.The theoretic curve is consistent with the experimental results about measuring superconducting film,especially when the third-harmonic voltage just exceeds zero.The J c value of superconducting films determined by the inductive method is also compared with results measured by four-probe transport method.The agreements between inductive method and transport method are very good. 相似文献
12.
E. G. Lokk M. P. Temiryazeva V. I. Shcheglov 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(10):1352-1354
The domain structure (DS) of yttrium-iron garnet films with uniaxial anisotropy fields higher than ∼120 Oe was found to have
a 3D character: there is a stripe domain structure of a certain type in the surface layer and a structure of another type
in the film bulk. It was revealed that in the absence of an external magnetic field, the boundaries of both DSs are almost
perpendicular, whereas with an increase in an external field applied in the film plane along the boundaries of the interior-volume
DS, the boundaries of the surface DS are gradually reoriented along the external field. This phenomenon is theoretically explained
on the basis of the micromagnetic model, which describes DS formation in ferrite films. 相似文献
13.
E. S. Kovalenko 《Russian Physics Journal》1992,35(7):619-625
Analysis of the propagation of surface acoustic waves (SAW) was carried out in piezoelectric-high-temperature superconductor (HTSC) film-dielectric structure near the superconducting transition of the HTSC film. By considering a change in the resistive state of the film, its inhomogeneity in a direction perpendicular to the substrate, and the mechanical load of the piezoelectric, equations describing the temperature dependence of the velocity and attenuation of the SAW were obtained. Our calculations agree with experimental results for LiNbO3-YBa2Cu3O7 structures if possible inhomogeneities in the film are taken into account.Institute for Automated Control Systems and Radio Electronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 38–45, July, 1992. 相似文献
14.
报道了在蓝宝石衬底上制备CeO2缓冲层的原位双温工艺法及其对Tl2Ba2CaCu2O8(Tl-2212)薄膜超导特性的影响.XPS和AFM测试结果表明,采用原位双温工艺法制备缓冲层,具有工艺简单,薄膜表面光滑,衬底材料原子扩散量少等特点.在先驱膜的高温后退火过程中,40 nm厚的CeO2薄膜就能有效地阻挡衬底材料对超导薄膜底层的扩散.随后制备厚度为530 nm的Tl-2212
关键词:
Tl-2212超导薄膜
蓝宝石
氧化铈缓冲层
原位双温工艺法 相似文献
15.
The generation of acoustic and vortex oscillations in high-temperature superconductor (HTSC) powders excited by radiofrequency (rf) pulses was analyzed in detail in our earlier publications. The rf magnetic field stimulates oscillations of magnetic vortices on the surface of an HTSC grain, which are transformed into lattice vibrations via the pinning centers at the surface, thus inducing a propagating acoustic wave. The allowance for second-order nonlinearity in the gradient of deviation of the crystal lattice from its equilibrium position in the equation for the acoustic wave leads to a dependence of the natural frequency of crystal lattice vibrations on the amplitude and duration of pulses exciting these vibrations. Such a dependence is responsible for echo signals that can be detected experimentally. The proposed model makes it possible to interpret most experimental results for BiPbSrCaCuO superconducting samples. We consider the effect of a constant magnetic field on the amplitude and the echo signal decay time. We observed a clearly manifested peak that was not described by other authors. The model proposed here provides an obvious explanation for this peak. 相似文献
16.
M. A. Zelikman 《Physics of the Solid State》2000,42(10):1813-1818
A theoretical explanation is proposed for the experimental results on the behavior of higher harmonics of the granular HTSC response to a variable magnetic field of frequencies ~102 Hz. The theory explains the periodicity in the dependence of the harmonics amplitudes on a static external magnetic field; the dependence of the period on the harmonics number and on the amplitude of the variable magnetic field; the existence of the threshold in the dependence of the odd-harmonics amplitudes on the amplitude of the variable magnetic field; and the possible formation of pairs for these dependences for the neighboring odd harmonics. It is shown that the experimental dependences can be explained without a detailed analysis of microprocesses in individual Josephson loops only by treating HTSC as a macroscopic medium characterized by the dependence Φ(H) of the magnetic flux on the external magnetic field, which is typical of type II superconductors. 相似文献
17.
It is shown that, in an edge superconducting layer of a thin film in a magnetic field perpendicular to the film plane, phase slip centers are formed. The centers arise below the superconducting transition temperature because of the thermal fluctuations of the order parameter and lead to the suppression of superconductivity. The resistance corresponding to such fluctuations is determined, and the contribution of the Aslamazov-Larkin correction to the conductivity of a thin film in magnetic fields slightly exceeding the critical field that breaks the surface superconductivity is calculated. 相似文献
18.
The new class of phenomena described in this review is based on the interaction between spatially separated, but closely located ferromagnets and superconductors, the so-called ferromagnet–superconductor hybrids (FSH). Typical FSH are: coupled uniform and textured ferromagnetic and superconducting films, magnetic dots over a superconducting film, magnetic nanowires in a superconducting matrix, etc. The interaction is provided by the magnetic field generated by magnetic textures and supercurrents. The magnetic flux from magnetic structures or topological defects can pin vortices or create them, changing the transport properties and transition temperature of the superconductor. On the other hand, the magnetic field from supercurrents (vortices) strongly interacts with the magnetic subsystem, leading to formation of coupled magnetic–superconducting topological defects. The proximity of ferromagnetic layer dramatically changes the properties of the superconducting film. The exchange field in ferromagnets not only suppresses the Cooper-pair wavefunction, but also leads to its oscillations, which in turn leads to oscillations of observable values: the transition temperature and Josephson current. In particular, in the ground state of the Josephson junction the relative phase of two superconductors separated by a layer of ferromagnetic metal is equal to?π?instead of the usual zero (the so-called π-junction). Such a junction carries a spontaneous supercurrent and possesses other unusual properties. Theory predicts that rotation of magnetization transforms s-pairing into p-pairing. The latter is not suppressed by the exchange field and serves as a carrier of long-range interaction between superconductors. 相似文献
19.
Microwave filters based on granular high-temperature superconducting structures are studied. Filters with granular kinetic inductance are very sensitive to the changes in temperature, constant magnetic field, and transport current flowing through a high-temperature superconducting film. The tuning sensitivity to temperature, constant magnetic field, and transport current is, on average, 9292 kHz/deg, 185.65 kHz/G, and 26.8 kHz/nA, respectively. 相似文献
20.
A. N. Artemov 《Journal of Experimental and Theoretical Physics》2000,91(6):1213-1220
The thermodynamic potential of a system of Peierls vortices in a thin superconducting film, containing radiation defects, in a perpendicular external magnetic field is calculated. The equilibrium temperature dependences of the densities of free vortices and vortices trapped by defects are found in the mean-field approximation for various magnitudes of the external field. It is shown that the equilibrium magnetization of a thin superconducting film exhibits the same features that were observed experimentally in the reversible magnetization of high-temperature superconductors. An asymptotic expression is obtained for the difference of the magnetizations of perfect and irradiated films. According to this expression, the difference depends on the pinning energy of a vortex on a defect and the density of defects. 相似文献