共查询到20条相似文献,搜索用时 15 毫秒
1.
A. É. Primenko V. D. Kuznetsov N. D. Kushch É. B. Yakubskii 《Journal of Experimental and Theoretical Physics》1997,85(2):415-416
This papr discusses the results of the first investigation of the magnetic properties of the organic superconductor λ-(BETS)2GaCl4. It is shown that the transition to the superconducting state begins at T
c≈7 K, which is considerably lower than the value T
c≈10 K determined from resistive measurements. The estimated value of the critical current density turns out to be two orders
of magnitude lower than in superconductors of the family κ-(ET)2
X.
Zh. éksp. Teor. Fiz. 112, 760–762 (August 1997) 相似文献
2.
The magnetic properties of YBa2Cu3O7−x
ceramics of various densities and Bi2Sr2CaCu2O8 quasicrystals irradiated with neutrons at fluences of 1016–1019 cm−2 are investigated by a radio-frequency method (in the frequency range f=100–150 MHz). The electromagnetic absorption is used to estimate the parameters of a Josephson medium: the lower critical
field, the critical current density, the grain size and intergranular distances, and the penetration depth of the magnetic
field in the sample. The hysteresis of electromagnetic absorption in the indicated superconductors is investigated; the hysteresis
effect can be used to obtain data on flux pinning processes and flux creep dynamics. It is shown that an increase in the critical
current density is observed as a result of the injection of radiation-induced pinning centers.
Fiz. Tverd. Tela (St. Petersburg) 39, 28–34 (January 1997) 相似文献
3.
The equations of motion for a charged particle in crossed magnetic and electric fields are used to make a numerical simulation
of the operation of a magnetic resonance mass spectrometer for which the ion trajectory in the analyzer is divided into various
sections. The calculations take into account the real structural dimensions and the parameters of the main components and
systems and also allow for its operating characteristics in various regimes, as obtained by investigating a prototype. The
calculation s yield the optimum geometric, electrical, frequency, phase, and magnetic parameters of the device, for which
one can achieve a resolution R
5096≈1.35×106 and a current efficiency K
I
≈0.006.
Zh. Tekh. Fiz. 69, 89–96 (April 1999) 相似文献
4.
The onset of specific magnetic structures associated with the formation of extended current filaments is observed in YBCO
single crystals in a rotating magnetic field. Like current filaments in a plasma, they are unstable and decay into current
macrovortices. The appearance of filaments is explained by the formation of closed flux rings along magnetization-reversal
fronts and collapse of these rings with formation of Meissner cylinders. The total current along the surface and in the vortex
shell of the cylinder (the latter current dominates in high-T
c
superconductors) exceeds the critical current in the same volume located far from a filament.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 3, 253–257 (10 February 1997) 相似文献
5.
É. V. Matizen P. P. Bezverkhii V. G. Martynets 《Journal of Experimental and Theoretical Physics》1997,84(3):578-583
We establish how trapped magnetic flux depends on the frequency and amplitude of an alternating field and how such a field
affects the relaxation rate of the flux. We find that the nature of the flux creep changes in the process and that relaxation
of the flux stops after the external field is switched off. We examine the dynamics of flux relaxation in a ring in the approximation
in which the current density is assumed homogeneous, for various density dependences of the effective vortex activation energy.
The critical current density and the vortex activation energy are obtained as functions of the external field strength. Finally,
we explain the observed behavior in terms of the different field profiles emerging in the rings.
Zh. éksp. Teor. Fiz. 111, 1047–1056 (March 1997) 相似文献
6.
The NMR of 55Mn in the quasi-one-dimensional noncollinear anti-ferromagnet CsMnI3 is investigated at T=1.3 K in magnetic fields up to ∼80 kOe and angles between the field and C
6 axis ϕ≈ 0.5° and ϕ=7°. A new reorientational magnetic phase transition is observed in a field H
c1≈39.0 kOe. The magnetic structure for H>H
c1 is determined. The average Mn2+ spins of the magnetic sublattices in the new phase are determined from an analysis of the NMR spectrum to be 〈 S
C
〉=1.63 and 〈S
D
〉=1.72.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 12, 988–993 (25 June 1998) 相似文献
7.
R. M. Arutyunyan V. L. Ginzburg G. F. Zharkov 《Journal of Experimental and Theoretical Physics》1997,84(6):1186-1196
The question of a surface barrier which determines the behavior of a vortex in a hollow superconducting cylinder of finite
thickness in an external magnetic field is discussed, taking into account magnetic flux quantization in the cavity. The behavior
of magnetic vortices in a hollow superconductor in the presence of a thermoelectric current is also considered. Pairs of magnetic
vortices with opposite magnetic field orientations (vortex-antivortex pairs) are generated by this current near T
c. The thermoelectric current drives the antivortex (the vortex with oppositely directed field) out of the cylinder, whereas
the vortex is ejected into the cavity and remains on the inside cylinder surface as a current. The number of magnetic flux
quanta trapped inside the cylinder increases by one. The relation of this mechanism to the “giant” thermoelectric effect in
hollow superconductors is discussed.
Zh. éksp. Teor. Fiz. 111, 2175–2193 (June 1997) 相似文献
8.
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
9.
V. A. Ryzhov P. L. Molkanov A. V. Lazuta V. V. Runov V. P. Khavronin I. O. Troyanchuk 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(10):1477-1480
We present the results from studying the magnetic properties (linear and nonlinear susceptibilities and the depolarization
of polarized neutrons) of Nd1 − x
Ba
x
MnO3 manganite, x = 0.3, with Curie temperature T
C ≈ 140 K and dielectric-to-metal transition temperature T
DM ≈ 129 K. Its critical behavior corresponds to that of an isotropic 3-D ferromagnet at temperatures above T*≈ 144 K, but a strong nonlinear response in weak magnetic fields and depolarization are observed at temperatures below T*. It is shown that this nontraditional behavior is related to the generation of ferromagnetic clusters in the paramagnetic
matrix that form a conducting percolative network at temperatures near T
DM. 相似文献
10.
V. A. Moshnikov A. V. Moshnikov A. I. Rumyantseva S. A. Nemov R. V. Parfen’ev A. V. Chernyaev 《Physics of the Solid State》1999,41(4):550-555
A reliable technique of local chemical characterization of multicomponent semiconductor solid solutions has been developed,
and the possibility of its application to the SnTe-SnSe quaternary solid solutions doped with 16 at.% In verified. The behavior
of the electrical resistivity of samples of these solid solutions at low temperatures, 0.4–4.2 K, has been studied. The critical
temperature T
c and the second critical magnetic field H
c2 of the superconducting transition and their dependences on the solid-solution composition have been determined. The superconducting
transition at T
c≈2–3 K is due to hole filling of the In-impurity resonance states, and the observed variation of the superconducting transition
parameters with increasing Se content in the solid solution is related to the extrema in the valence band and the In band
of resonance states shifting with respect to one another.
Fiz. Tverd. Tela (St. Petersburg) 41, 612–617 (April 1999) 相似文献
11.
Magnetoplastic effect in irradiated NaCl and LiF crystals 总被引:2,自引:0,他引:2
V. I. Al’shitz E. V. Darinskaya O. L. Kazakova 《Journal of Experimental and Theoretical Physics》1997,84(2):338-344
The effect of low x-ray irradiation doses (≈102 rad) on the magnetoplastic effect — the detachment of dislocations from paramagnetic centers under the action of an external
magnetic field B — in alkali-halide crystals has been investigated. The measurements were performed on LiF crystals and three types of NaCl
crystals, differing in impurity content. The dependence of the mean free path l of the dislocations on the rotational frequency ν of a sample in a magnetic field was especially sensitive to low irradiation doses. In unirradiated crystals this dependence
is a single-step dependence and is characterized by a critical frequency ν
c ∝B
2 above which the magnetoplastic effect is not observed. The frequency ν
c depends only on the type of paramagnetic centers, and not on their density. Even the lowest irradiation dose employed (<100
rad) leads to a sharp restructuring of the dependence l(ν), converting it into a two-step dependence (for edge dislocations) with an additional critical frequency ν
c2, that is insensitive to the irradiation dose, and that corresponds to the appearance of magnetically sensitive stoppers
of a new type under irradiation. The initial critical frequency ν
c1, as a rule, also varies with the dose, reflecting the change in state of the impurity complexes (Ca in NaCl and Mg in LiF).
Specifically, it is shown for NaCl(Ca) crystals that as the irradiation dose increases, the frequency ν
c1 increases, gradually approaching the value ν
c2, so that by the time the dose is ≈300 rad, the dependence l(ν) once again becomes a single-step dependence, dropping sharply only for ν⩾ν
c2. It is shown that the addition of a small number of Ni atoms to a NaCl crystal makes the Ca complexes radiation resistant,
and the critical frequency ν
c1 corresponding to them initially equals ν
c2 for crystals with no Ni. The recombination kinetics of radiation defects in the case in which the samples are irradiated
under a tungsten lamp was investigated. A possible physical model of the observed dependences is discussed.
Zh. éksp. Teor. Fiz. 111, 615–626 (February 1997) 相似文献
12.
S.-G. Cheng Y. X. Xing X. C. Xie Q.-F. Sun 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(4):551-557
The Josephson current through an Aharonov-Bohm (AB)
interferometer, in which a quantum dot (QD) is situated on one arm
and a magnetic flux Φ threads through the ring, has been
investigated. In the presence of the magnetic flux, the relation
between the Josephson current and the superconductor phase is
complex, and the system can be adjusted to π junction by either
modulating the magnetic flux or the QD’s energy level
εd. Due to the electron-hole symmetry, the Josephson
current I has the property
I(εd,Φ)=I(-εd,Φ+π). The Josephson
current exhibits a jump when a pair of Andreev bound states aligns
with the Fermi energy. The condition for the current jump is given.
Particularly, we find that the position of the current jump and the
position of the maximum value of the critical current Ic are
identical. Due to the interference between the two paths, the
critical current Ic versus the QD’s level εd shows a
typical Fano shape, which is similar to the Fano effect in the
corresponding normal device. However they also show some
differences. For example, the critical current never reaches zero
for any parameters, while the current in the normal device can reach
zero at the destruction point. 相似文献
13.
Karen B. Paul 《Central European Journal of Physics》2005,3(1):115-126
A monocrystal ofFe
3
O
4 is characterized by resistance, magnetoresistance and magnetic measurements in a temperature range from 4.2 K to 350 K and
magnetic field-cycling from −9 T to 9 T. The resistance measurements revealed a metal-insulator Verwey transition (VT) atT
v
=123.76 K with activation energy E=92.5 meV at T >T
v
and temperature-substitute for the activation energy below the VT,T
0=E/k
B
≈3800 K within 70 K–110K. The magnetotransport results independently verified the VT at 123.70 K, with discontinuous change
in the magnetic moment ΔM≈0.21 ΔM≈0.21μ
B
and resistance hysteresis, dependent on the magnetic field in a narrow temperature range of 0.4° around theT
v
. The magnetic characterization established self consistentlyT
v
as ≈123.67 K, the jump in the magnetization at the VT≈0.25μ
B
and confirmed, that the magnetocrystalline anisotropy is the main microscopic mechanism responsible for the magnetization
of the monocrystal (88%) with additional natural and imposed defects contributing as 12%. 相似文献
14.
The influence of variously oriented uniform magnetic fields on the cathodic attachment of a low-current vacuum arc with electrodes
made of oxygen-free copper and CuCr30 composition is studied. It is found that, if the current is fixed, cathode spots in
the arc attachment are distributed by the normal law in the entire range of variation of the amplitude of magnetic induction
vector B and angle α between this vector and the normal to the cathode surface. The parameters of the distribution depend on the magnetic
field and cathode material. The magnetic field dependence is appreciable only when angle α exceeds some critical value α*
(α* ≈ 30° and ≈45° for cathodes made of copper and CuCr30, respectively). At α > α*, the parameters of the distribution become
strongly dependent on α, while the B dependence remains weak. Only when α → π/2 does the field amplitude have a pronounced effect on the parameters of the distribution.
From the obtained results, we determine the statistical characteristics of the distribution of the mean current transmitted
by a cathode spot in variously oriented magnetic fields. The found relationships make it possible to explain the peculiarities
of the structure of the cathodic attachment of the high-current vacuum arc stabilized by an external axial magnetic field. 相似文献
15.
The current-voltage characteristics of granular YBa2Cu3O6.95 high-temperature superconductor samples have been measured at a temperature of 77.3 K in external transverse magnetic fields
H
ext with a strength of up to H
ext ≈ 500 Oe for low transport current densities (0.1 A/cm2 ≤ j ≤ 0.6 A/cm2). The current-voltage characteristics obtained have been used to construct dependences of the magnetoresistance ρ on the
quantities j (ρ(j)
Hext=const) and H
ext(ρ(H
ext)
j = const). It has been revealed that the current and field dependences of the magnetoresistance exhibit anomalies at H
ext ≥ H
c1g
, where H
c1g
is the lower critical field of superconducting grains. A comparative analysis of the dependences ρ(j)H
ext = const and ρ(H
ext)
j = const has made it possible to develop concepts regarding the influence of the processes of redistribution of the magnetic field
between grain boundaries and superconducting grains on the transport and galvanomagnetic properties of granular high-temperature
superconductors. It has been established that the field dependences of the magnetoresistance exhibit specific features associated
with the beginning of penetration of Josephson vortices into grain boundaries in the magnetic field H
c1J
and with the breaking of a continuous chain of Josephson junctions in the magnetic field H
c2J
. 相似文献
16.
The critical current J
c(θ) of an intergrain boundary is calculated as a function of the contact misorientation angle θ of the granules. It is assumed that the ordering parameter is suppressed in regions near boundaries with an enhanced mechanical
stress induced by randomly distributed surface dislocations. The stress distribution function is determined using a probabilistic
approach. Assuming that the weak coupling at the boundary is Josephson coupling, an analytic expression is found for the angular
dependence J
c(θ) (for tilt and twist boundaries). The magnitude of the residual critical current of a boundary in a strong magnetic field
is estimated.
Fiz. Tverd. Tela (St. Petersburg) 40, 393–402 (March 1998) 相似文献
17.
A contactless microwave method is used to measure the fast magnetic relaxation of granular ceramic samples of YBa2Cu3O7−x
irradiated by neutrons with fluences of 1016–1019 cm−2. An experimental study of the time dependence of the relaxation of high-frequency (rf) absorption (f=100 MHz) after the action of an external magnetic field pulse has shown the magnetic relaxation times τ
0 to be in the time interval of 0.5–150 ms. The rf-absorption mechanism is discussed in terms of an intergranular system with
a thermally activated flux of vortices and their diffusion in the granular medium.
Fiz. Tverd. Tela (St. Petersburg) 39, 977–981 (June 1997) 相似文献
18.
The transformation of the band structure of LaCoO3 in the applied magnetic field has been theoretically studied. If the field is below its critical value B
C
≈ 65 T, the dielectric band gap decreases with the field, thus giving rise to negative magnetoresistance that is highest
at T ≃ 300–500 K. The critical field is related to the crossover between the low- and high-spin terms of Co3+ ions. The spin crossover results in an insulator-metal transition induced by an increase in the magnetic field. 相似文献
19.
P. N. Bukivskii Yu. P. Gnatenko A. Kh. Rozhko O. A. Shigil’chev 《Physics of the Solid State》1997,39(3):458-465
It is shown that the temperature dependence of the binding energy of exciton-impurity complexes in the semimagnetic semiconductors
Cd1−x
MnxTe (x≈0.05) is described well in the donor-electron model with an effective characteristic magnetic-polaron energy. The contributions
of the average exchange field and of thermodynamic fluctuations of the magnetization to the binding energy and their variation
with temperature with and without a weak magnetic field (H⩽3.5 kOe) are determined. How doping with scandium, vanadium, and cobalt effects the appearance of the magnetic-polaron in
the experimental crystals was studied.
Fiz. Tverd. Tela (St. Petersburg) 39, 527–535 (March 1997) 相似文献
20.
A. I. Dmitriev R. B. Morgunov S. V. Zaitsev 《Journal of Experimental and Theoretical Physics》2011,112(2):317-326
The static and high-frequency dynamic magnetic properties and photoluminescence of two-dimensional semiconductor GaAs heterostructures
containing an InGaAs quantum well and a thin manganese layer (δ layer) are studied. It is found that the Curie temperature
is T
C ≈ 35 K and the magnetic anisotropy field of the ferromagnetic manganese δ layer is H
a ≈ 600 Oe. The spin resonance spectrum exhibits a line in weak fields (from −50 to 100 Oe), which is observed in the same
temperature interval T < 40 K where the ferromagnetic ordering of the manganese δ layer occurs. This line is probably caused by the nonresonance
contribution of the spin-dependent scattering of charge carriers to the negative magnetic resistance. The dependence of the
degree of polarization of photoluminescence on the magnetic field also points to the ferromagnetic behavior of the manganese
δ layer. 相似文献