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1.
M. A. Zelikman 《Technical Physics》2009,54(9):1290-1300
A new approach based on analysis of continuous configurational modification in the direction of a decrease in the Gibbs potential
is proposed for computing the penetration of an external magnetic field in an ordered 3D Josephson medium. The configuration
to which the Meissner state passes when the external field slightly exceeds the Meissner stability threshold is determined.
This configuration contains a periodic sequence of linear vortices with centers lying in an alternating cell, parallel to
the boundary, and located at a certain distance from it. A further increase in the field reveals that the 3D medium behaves
like a long periodically modulated Josephson junction. However, the critical value I
C
of the pinning parameter for a 3D medium, which lies in the interval 0.7–0.8, is lower than the analogous value I
C
= 0.9716 for a long junction. The values of H
max for I < I
C
, as well as the steepness of the decrease in the magnetic field at the boundary for I > I
C
, are higher in the 3D medium than in a long junction. For very large values of I, the field penetrates the boundary region not as a 2D lattice of linear vortices, but as a 1D lattice of plane vortices,
which are mathematically equivalent to the vortices in a long junction. 相似文献
2.
M. A. Zelikman 《Technical Physics》2009,54(12):1742-1748
The configurations of currents and the profile of a magnetic field penetrating into a finite-length contact at I < I
C
are calculated. The computational method is based on analyzing the continuous variation of the current structure leading
to a decrease in the Gibbs potential. Such an approach makes it possible to find a configuration that sets in when an external
field slightly exceeds H
max and trace the evolution of this configuration with increasing field. It is shown that at H > H
max boundary structures turn into quasi-uniform sequences of vortices the spacing between which oscillates about a mean value
decreasing with increasing H. At some values of H, vortices with a number of fluxoids Φ0 larger by unity start penetrating into the contact in the form of boundary sequences. As the field grows, they produce quasi-uniform
sequences, etc. Vortices with the number of fluxoids Φ0 differing by more than unity can fall into the contact at no field. The penetration of vortices with (k + 1)Φ0 into a contact each cell of which contains kΦ0 is fully identical to the penetration of vortices with one Φ0 into the Meissner configuration. This statement is supported by the almost strict periodicity of mean induction b in the contact versus external field h dependence with a period of 1 along both axes and also by the form of the dependences of the magnetic field in the cells
on the cell-boundary distance. 相似文献
3.
M. A. Zelikman 《Technical Physics》2010,55(11):1588-1595
The Meissner state of a 3D Josephson medium is analyzed for stability against small fluctuations of phase discontinuities
at contacts. For any form of fluctuations, there exists value I
0 of pinning parameter I such that the Meissner configuration remains stable if I < I
0. Reasons why the configuration remains stable at small I are considered. Instability arises when the quadratic form of the second variation of Gibbs potential G is not a positively definite quantity. At small I, the contribution of the Josephson energy to G is small. The second variation of the magnetic energy, the other component of G, is always a positively definite quadratic form. Therefore, instability may arise only if I has a finite value. This statement holds true not only for the Meissner but also for any equilibrium configuration. At I < I
0, stability persists up to the boundary of the Meissner state. Then, a sequence of plane vortices parallel to the boundary
appears throughout the sample. Thus, vortices appearing at I < I
0 are plane vortices rather than linear. The configurations of currents and the magnetic field profile inside the sample are
calculated for I < I
0. Calculation is based on analyzing the continuous variation of the current configuration toward a decrease in the Gibbs potential. 相似文献
4.
M. A. Zelikman 《Technical Physics》2014,59(11):1610-1615
The results of calculation of penetration of an external magnetic field into a 3D ordered Josephson medium, based on analysis of modification of the configuration in the direction of the decrease in its Gibbs potential, are reported. When the external field slightly exceeds the stability threshold, the Meissner configuration is transformed into a periodic sequence of linear vortices, which are parallel to the boundary of the medium and are located at a certain distance from it. There exists a critical value I C separating two possible regimes of penetration of the external magnetic field into the medium. For I > I C , for any value of the external field, a finite-length boundary current configuration appears, which completely compensates the external field in the bulk of the sample. At the sample boundary, the field decreases with increasing depth almost linearly. The values of the slope of the magnetic field dependence are rational fractions, which remain constant in finite intervals of I. When the value of I exceeds the upper boundary of such an interval, the slope increases and assumes the value of another rational fraction. If, however, I < I C , such a situation takes place only up to a certain value of external field H max. For higher values, the field penetrates into the medium to an infinite depth. These results lead to the conclusion that the Bean assumptions are violated and that Bean’s model is inapplicable for analyzing the processes considered here. 相似文献
5.
M. A. Zelikman 《Technical Physics》1997,42(9):1019-1026
The behavior of planar (laminar) vortices in a three-dimensional, ordered Josephson medium as a function of the parameter
I, which is proportional to the critical junction current and the cell size, is investigated with allowance for pinning due
to the cellular structure of the medium. The minimum possible distances between two isolated vortices are calculated. A system
of vortices formed in a sample in a monotonically increasing external magnetic field is analyzed. The minimum distance from
the outermost vortex to the nearest neighbor is proportional to I
−1.1. For I⩽1.3 each vortex contains a single flux quantum Φ0, and the distance between them does not decrease in closer proximity to the boundary but remains approximately constant,
implying that the magnetic field does not depend on the coordinate in the region penetrated by vortices. These facts contradict
the generally accepted Bean model. The sample magnetization curve has a form typical of type II superconductors. Allowance
for pinning raises the critical field H
c and induces a sudden jump in the curve at H=H
c.
Zh. Tekh. Fiz. 67, 38–46 (September 1997) 相似文献
6.
M. A. Zelikman 《Technical Physics》2009,54(2):197-203
A new approach to magnetic field profiling inside a Josephson contact is suggested. Its essence consists in analyzing continuous
variation of a current configuration leading to a decrease in the Gibbs potential. With this approach, one can find a configuration
into which the Meissner state turns when an external field slightly exceeds the upper boundary of the Meissner regime and
trace the evolution of this configuration with increasing field. Calculations show that there exists critical value I
c of the pinning parameter in the range 0.95–1.00. This critical value separates two possible conditions of magnetic field
penetration into the contact. At I > I
c, a near-boundary current configuration completely compensating for the external field inside the contact arises irrespective
of the external field strength. At I < I
c, such a situation is observed only until the external field strength exceeds certain value H
max. Higher fields penetrate into the contact indefinitely deep. In nearboundary configurations, the magnetic field drops with
increasing depth almost linearly. Its slope k has rational values, which remain constant within finite intervals of I. As I goes beyond a given interval, k rises stepwise and takes on another rational value. When an external magnetic field is switched on adiabatically, configurations
with a maximal growth rate of the magnetic field are observed. 相似文献
7.
M. A. Zelikman 《Physics of the Solid State》1997,39(11):1751-1755
A system of pancake vortices formed near the boundary of a sample in a monotonically increasing external magnetic field is
calculated with allowance for pinning due to the cellular structure of the medium for various values of the pinning parameter
I, which is proportional to the critical current of the junction and the cell diameter. The shortest distance from the outermost
vortex to the nearest neighbor is proportional to I
−11. It is shown that the pinning parameter has a critical value I
c separating two regimes with different types of critical states. For I<I
c the external magnetic field has a threshold value H
t(I), above which the field immediately penetrates the interior of the junction to an infinite distance. For I>I
c the magnetic field decays linearly from the boundary into the interior of the junction. The value obtained in the study,
I
c=3.369, differs from the value of 0.9716 postulated by other authors. The dependence of the slope of the magnetic field profile
near the boundary on I is determined. It is shown that the slope is independent of I in intervals 2πk<I<2πk+π.
Fiz. Tverd. Tela (St. Petersburg) 39, 1958–1963 (November 1997) 相似文献
8.
Magnetic flux trapping (MFT) in granular YBa2Cu3O7 − δ high-temperature superconductors (HTSCs) is studied. At T = 77.36 K, the dependence of the hysteresis of the transverse magnetoresistance on transport current I and the maximum value of external magnetic field H
ext is found in the measurement cycle 0 → H
extmax → 0. The dependences of the parameters characterizing MFT, namely, residual magnetoresistance, field H
min at which the magnetoresistance is minimal, and the magnetoresistance at H
ext = H
min, on I and H
extmaxare determined. MFT is found to occur in HTSC granules under the action of an external magnetic field exceeding the lower
critical field of superconducting granules H
c1A, and the transport current only weakly affects the magnitude of MFT. 相似文献
9.
A. A. Zhukov G. K. Perkins A. D. Caplin H. Kupfer T. Wolf 《Czechoslovak Journal of Physics》1996,46(Z3):1773-1774
The magnetic moments parallel and perpendicular to thec-axis (measured simultaneously) have been studied as a function of direction of applied magnetic fieldH in twinned and de-twinned YBa2Cu3O7−δ single crystals. They show pronounced anomalies when the field direction approaches thec-axis. These allow clear identification of the angle ϕL at which vortices are locked into twin planes. Complete shielding of theH
ab field component (transverse Meissner effect) was observed in the locked state. For larger angles, up to ϕT, the vortices continue to be non-collinear with the applied field, but their direction deviates from the trapping plane.
ϕL exhibits a 1/H field-dependence, whereas ϕT shows only weak logarithmic variations withH. 相似文献
10.
G. M. Maksimova 《Physics of the Solid State》1998,40(10):1607-1610
The mixed state of thin narrow superconducting films with an edge barrier placed in a transverse magnetic field is considered.
The boundaries of the region for the existence of metastable mixed states with an assigned number of vortices N [H
min(N)⩽H⩽H
max(N)] are found. The magnetic-field dependence of the critical field is found for the films. The transition from the Meissner
state to the static mixed state is discussed.
Fiz. Tverd. Tela (St. Petersburg) 40, 1773–1777 (October 1998) 相似文献
11.
M. A. Zelikman 《Technical Physics》2007,52(10):1316-1321
The upper field of the Meissner regime, H up, and overheat field H′c1, above which vortices start penetrating into a Josephson contact, are calculated throughout the range of pinning parameter I. The stability of likely configurations is investigated. It is shown that H up = H′c1 at any I. The existence of a single vortex centered at the extreme cell in the contact is demonstrated to be a possibility. At I > 3.69, such a vortex may exist even in a zero magnetic field. At 1.48 < I < 3.69, this vortex can exist in an external field in the range from some H v to H up. At I < 1.48, the vortex cannot exist under any conditions. From the equality of H up and H′c1 at any I, the conclusion is drawn that penetration of vortices into any Josephson medium is conditioned by the need to satisfy flux quantization conditions. Here, not the forces of vortex pinning at defects in the medium but quantization requirements are of major importance, which are satisfied in specific quantum ways rather than by meeting equilibrium conditions for vortices, forces, etc. 相似文献
12.
V. N. Zavaritskii 《JETP Letters》1999,70(8):556-562
The effect of a magnetic field H⊥(ab) on the transverse current-voltage characteristics (IVCs) of the mixed state of a single crystal of the layered superconductor
Bi2Sr2CaCu2Oy (BSCCO) is investigated. It is established that in a wide range of temperatures and fields above the irreversibility line
the initial part of the IVC is described by the law V∝I
γ with γ≃1. As the current increases further, this law is replaced by a section where V∝exp(I). It is established that the multivalued, multibranch characteristics, interpreted as a manifestation of an internal Josephson
effect, do not change appreciably when the crystal passes into a state with nonzero linear resistance. The character of the
dependence of the characteristic switching current on the first resistive branch, I
J
(H,T), is determined.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 543–548 (25 October 1999) 相似文献
13.
D. M. Zashchirinskii L. I. Koroleva A. S. Morozov Yu. V. Dolzhenkova 《Physics of the Solid State》2011,53(2):316-319
The magnetocaloric effect ΔT has been studied by a direct method in two samples of the manganite Sm0.55Sr0.45MnO3, namely, a single crystal (sample A) and a ceramic sample (sample C). The temperature dependences of the ΔT effect of both samples exhibit a maximum at T
max = 143.3 K for the sample A and T
max = 143 K for the sample C. In these maxima, the values of the ΔT effect are 0.8 and 0.4 K in the magnetic field H = 14.2 kOe for the samples A and C, respectively. In addition, the ΔT(T) curve of the sample A has a minimum at T
min = 120 K, in which ΔT = −0.1 K. The maximum value of the ΔT effect increases with an increase in the magnetic field H in the range of magnetic fields up to 14.2 kOe, and the rate of this increase at H > 8 kOe is higher than that at H < 8 kOe. These features of the ΔT effect are explained by the presence of ferromagnetic and antiferromagnetic A- and CE-type clusters in the samples. 相似文献
14.
The field dependence of the vibrational contribution to the dynamic magnetic permeability μ
V(H) is calculated for a thin (of thickness d∼λ) high-T
c superconducting wafer in a magnetic field parallel to the surface. The resulting curves are plotted on the basis of an exact
numerical analysis of the vortex structures both for the thermodynamic-equilibrium vortex lattice and in the presence of pinning
forces and the Bean-Livingston surface barrier. It is shown that the μ
V(H) curves are highly sensitive to the size factor (d/λ) and exhibit abrupt changes corresponding to a change in the number of vortex rows. The equilibrium μ
V(H) curve is found to be similar in its general behavior and absolute value (obtained with allowance for the distribution of
grain sizes and with appropriate values of λ and ϰ) to the experimental μ
V(H) curve plotted at nitrogen temperature for fine-grained YBa2Cu3Ox with grain diameters 〈D〉∼λ in an increasing magnetic field. It is established that the main cause of the experimentally observed irreversible behavior
of the μ
V(H) curves during cyclic variation of the applied magnetic field is the existence of a surface barrier to the exit of vortices
from the superconductor. The lower limit H
min(B) of stability of the mixed state in the presence of an ideal surface barrier in a thin, high-T
c superconducting wafer (d∼λ) is determined, along with the range of the vortex state (H
max-H
min) for a fixed number of vortices in micrometer-size grains of the investigated YBaCuO samples.
Fiz. Tverd. Tela (St. Petersburg) 39, 1943–1947 (November 1997) 相似文献
15.
B V B Sarkissian A K Grover G Balakrishnan Ravi Kumar P L Paulose R Vijayaraghavan V Sankaranarayanan C K Subramanian 《Pramana》1992,38(6):641-667
The results of experimental studies on hysteresis in magnetization, thermomagnetic history effects, anomalous variations in
magnetic hysteresis curves and the decay rates of magnetization obtained under different thermomagnetic histories in specimens
of conventional and high temperature superconductors are presented. The Bean’s critical state model is considered adequate
to explain magnetic behaviour in conventional hard superconductors. The similarity in the general features of the results
of different experiments on specimens of the two families of superconductors underscores the efficacy of the said model to
understand some aspects of the macroscopic magnetic response of high temperature superconductors as well. For instance, the
isothermal magnetization hysteresis loop which comprises of magnetization curves along forward (−H
max to +H
max) and reverse (+H
max to −H
max) paths define an envelop within which all isothermal magnetization data along different thermomagnetic histories lie. There
exist inequality relationship between various field values identified asH
peak,H
I,H
II etc. in isothermal magnetization hysteresis as well as magnetic relaxation data. The entire field span of an isothermal magnetization
hysteresis data set can be considered to comprise of three parts corresponding to (M
rem(H)−M
FC(H)+M
ZFC(H)) being equal to, less than or greater than zero, whereM
rem(H) are the remanent magnetization values obtained on reducing field to zero after having the specimen in different applied
field (H) values. There are, however some situations amongst thermomagnetic history effects in specimens which show incomplete flux
trapping on field cooling, where the critical state model has been found inadequate. 相似文献
16.
Yu. A. Boikov I. T. Serenkov V. I. Sakharov V. A. Danilov V. V. Afrosimov 《Physics of the Solid State》2011,53(10):2049-2053
The structure, orientation, and the response of electroresistance to magnetic field H and varying temperature T have been studied for 30-nm-thick La0.67Ba0.33MnO3 (LBMO) films. The deviation of the [001] direction in manganite layers from the normal to the plane of the (LaAlO3)0.29 + (SrAl0.5Ta0.5O3)0.71 substrate strictly corresponds to the vicinal angle of the latter. The minimum yield determined from 227-keV proton scattering
spectra is 0.025, signifying a high order of the cationic sublattice in the films. The biaxial compression of stable nuclei
of the manganite phase affects their stoichiometry, thus contributing to the depletion of LBMO films in the alkaline-earth
element. The maximum electroresistance values have been observed in the films grown at T
max ≈ 320 K, a temperature about 20 K lower than the Curie temperature of the corresponding bulk single crystals, and the maximum
magnetoresistance (MR ≈ −0.42, μ0
H = 2 T) occurs at T ≈ 300 K. At low temperatures (T < T
max/3) and μ0
H < 0.45 T, the electroresistance response of LBMO films to a magnetic field materially depends on the anisotropic magnetoresistance
and the intensity of hole scattering from domain walls; when μ0
H > 0.5 T, the major current-carrier relaxation mechanism is the interaction with magnons. 相似文献
17.
Two possible equilibrium configurations of line vortices in a three-dimensional ordered Josephson medium for any value of structural factor b are considered: the center of the vortex coincides with the center of one of the cells and the center of the vortex is on one of the contacts. Infinite sets of equations describing these configurations are derived. The infinite set can be made finite if currents away from the center are neglected. The assumption b = 0 is shown to be valid if pinning parameter I is less than 0.25. For I > 0.25, the structures and energies of both configurations of line isolated vortices are calculated throughout the range of structural factor b. As structural factor b increases, phase jumps at the contacts, currents in the central part of the vortex, and the total energies of the vortices decrease in both configurations. This leads to a decrease in critical field H c1. For all values of I and b, the energy of the vortex centered on the contact is higher than that of the vortex centered in the middle of the cell. 相似文献
18.
An HTSC powder sample with grain (particle) diameter of 20–50 μm placed in a dc magnetic field B
0 and cooled to a temperature below the superconducting transition temperature was exposed to the radiofrequency (rf) pulsed
magnetic field B
∼ (B
∼ ⊥ B
0) at a carrier frequency of 30.7 MHz. Stable echo signals were recorded which followed different rf-pulse trains. This phenomenon
has the following mechanism. The rf magnetic field stimulates fluxoid oscillations on the HTSC grain surface, which are transformed
into lattice oscillations through the pinning centers and induce a propagating sound wave. The second-order nonlinearity with
respect to the gradient of the crystal lattice deviation from the equilibrium position taken into account in the sound wave
equation yields the dependence of the crystal lattice natural frequency on the amplitude and length of the pulses which excite
these oscillations. This dependence is responsible for the emergence of echo signals. 相似文献
19.
A new model of electronic vortices in plasma is studied. The model assumes that the profile of the Lagrangian invariant I, equal to the ratio I=Ω/n of the electronic vorticity to the electron density, is given. The proposed approach takes into account the magnetic Debye
scale r
B
≃B/4πen, which leads to breakdown of plasma quasineutrality. It is shown that the Abrikosov singular model cannot be used to describe
electron vortices in plasmas because of the fundamental limitation on the electron vorticity on the axis of a vortex in a
plasma. Analysis of the equations shows that in the model considered for the electronic vorticity, the total magnetic flux
decreases when the size r
0 of the region in which I≠0 becomes less than c/ωpe (ωpe is the electron plasma frequency). For ω
pe
r
0/c≪1, an electronic vortex is formed in which the magnetic flux decreases as r
0
2
and the inertial component predominates in the electronic vorticity. The structure arising as ω
pe
r
0/c⇒0 is a narrow “hole” in the electron density, which can be identified from the spectrum of electromagnetic waves in this
region.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 461–466 (10 April 1998) 相似文献
20.
V. V. Shelkovnikov Z. M. Ivanova A. I. Plekhanov E. V. Spesivtsev S. V. Rykhlitsky 《Journal of Applied Spectroscopy》2009,76(1):66-72
Thin-film formation of J-aggregated pseudoisocyanine iodide with long alkyl substituents C18H37 (PIC 2-18) and C10H21 (PIC 2-10) and ethyl substituents (PIC 2-2) with added anion was studied by spectrophotometry directly during spin-coating of its solutions. It is found that a bathochromic shift
of the monomer dye absorption band maximum and extensive growth of a J-peak that is not compensated by the monomer decrease
take place as the dye film forms. The refractive index and absorption coefficient of a solid dye thin film in monomeric (n
max = 2.1) and J-aggregated (n
max = 3.05) forms were measured as functions of the dispersion by spectral ellipsometry. The influence of a change in the local
field factor on the spectral properties of the pseudoisocyanine dye solution in the course of both spin-coating and solid
J-aggregated thin-film formation is considered.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 1, pp. 76–83, January–February, 2009. 相似文献