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1.
An experimental study is reported of the effect of an electric field E⩽120 MV/m and of temperature T on the critical current I
c and I-V characteristics of yttrium-based high-T
c superconducting ceramics. The materials studied were copper-deficient ceramics, YBa2Cu3−x
Oy (D samples), and YBa2Cu3−x
Oy/Agx ceramics [S samples with silver present in amounts equal to the copper deficiency (0⩽x⩽0.4)]. It has been established that in D samples at 77 K, the electric field increases I
c and reduces substantially R for I>I
c, whereas in S samples no field effect is observed. Measurements of the I
c(T) dependence near the critical temperature showed that they can be described for all samples by a relation of the type I
c
=const(1−T/T
c
)α, where α≈1 for the D samples, and α≈2 for the S samples. The results obtained suggest that the electric-field effect correlates with the existence in the ceramic of SIS-type weak links at grain boundaries.
Fiz. Tverd. Tela (St. Petersburg) 40, 1195–1198 (July 1998) 相似文献
2.
B. I. Smirnov T. S. Orlova A. N. Kudymov M. T. Lanagan N. Chen K. C. Goretta 《Physics of the Solid State》1997,39(11):1759-1761
An experimental study is reported of the influence of temperature (T), electric field polarity (±E), as well as of changes in the electrode/insulator/superconductor (E/I/S) measuring system on the field effect in the ceramic (BiPb)2Sr2Ca2Cu3Ox. It has been established that at 77 K and for E⩾60 MV/m the critical current I
c and conductivity of the sample increase for I>I
c, irrespective of the field polarity. For lower fields and a negative electrode potential the conductivity in an electric
field may decrease. The field effect decreases with increasing temperature, to practically vanish near T
c where the sample is still in superconducting state. Experiments carried out with more complex systems E/I/M/I/S and E/I/M/S (M stands for a metallic foil) support the conclusion that it is the external electric field that is responsible for the observed
effects.
Fiz. Tverd. Tela (St. Petersburg) 39, 1967–1970 (December 1997) 相似文献
3.
Results are presented of an investigation of the magnetic properties of dilute frustrated ferrimagnetic spinels Li0.5Fe2.5−x
GaxO4 (x=0.8–1.2), which characterize the main parameters of the ferrimagnetic state and provide evidence of local violation of collinear
spin ordering and frustrations. In particular, measurements were made of the concentration dependences of the magnetic moment
n
0(x) and the Curie point T
c
(x), the magnetization isotherms σ
T
(H) at T=4.2 K and H⩽10 kOe, and also the low-and high-field magnetization polytherms σ
H
(T). It was established that for x⩾0.8 in fields exceeding the technical saturation field H
s
∼2 kOe, the temperature dependences of the high-field magnetization σ
H
(T) between 4.2 and 230 K cannot be described by the Bloch T
3/2 law whereas this law is satisfied for undiluted Li spinel (x=0). Over the entire temperature range (4.2–230 K) the experimental curves σ
H
(T) may be approximated by σ
H
(T)=σ
0(1−AT
3/2 − BT
5/2) for x=0.8–1.0 and σ
H
(T)=σ
0[1−CT
3/2exp(μ(H−H
0)/k
B
T)] for x=1.1, 1.2, where μH
0∼15 K is the internal field produced by competition between exchange interactions and frustrations.
Fiz. Tverd. Tela (St. Petersburg) 40, 1075–1079 (June 1998) 相似文献
4.
V. E. Arkhipov V. E. Startsev V. P. Dyakina J. Klamut Ya. M. Mukovskii A. Czopnik 《JETP Letters》1998,68(1):42-46
Magnetization measurements were performed on a lanthanum manganite La0.9Sr0.1MnO3 single crystal in the temperature interval 4.2–300 K and magnetic field interval 50 Oe-55 kOe in two sample cooling regimes:
1) cooling down to 4.2 K in a high (55 kOe) magnetic field, and 2) cooling in a “zero” field. It is shown that the temperature
dependences of the magnetization M(T) are substantially different in these regimes. Pronounced anomalies of M(T) were observed at temperatures T*=103 K and T
c
=145 K. The first anomaly is attributed to a structural transition, while the second one corresponds to a ferromagnet-paramagnet
phase transition. The magnetization of a La0.9Sr0.1MnO3 single crystal in the cooling regimes studied shows typical “spin-glass” behavior.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 39–43 (10 July 1998) 相似文献
5.
N. N. Efimova 《Journal of Experimental and Theoretical Physics》1998,86(4):731-736
Using model objects consisting of dilute reentrant spinels Li0.5Fe2.5−x
GaxO4 with x=1.0–1.2, this paper describes the temperature dependence of the magnetic contribution to the heat capacity, C
m
(T), at H=0 and temperatures exceeding the freezing temperature (T
f
∼10 K) and, for T⩾4.2 K, the low-field magnetization σ
H
(T) and the saturation magnetization σ
S
(T), as well as the magnetization isotherms σ
T
(T) in fields of up to 10 kOe. The specific features of the behavior of the overall characteristics of C
m
(T) and σ
S
(T) are found for the states of a frustrated ferrimagnetic that occur in the conditions considered here (H=0 and T>T
f
or T⩾4.2 K and strong magnetic fields) and are discussed in connection with changes in the magnetic excitation spectrum caused
by local breakdowns of collinear spin ordering and frustrations.
Zh. éksp. Teor. Fiz. 113, 1339–1349 (April 1998) 相似文献
6.
Y. Kopelevich V. V. Lemanov S. Moehlecke J. H. S. Torres 《Physics of the Solid State》1999,41(12):1959-1962
Measurements of the basal-plane resistivity ρ
a(T,H) performed on highly oriented pyrolitic graphite, with magnetic field H∥c-axis in the temperature interval 2–300K and fields up to 8 T, provide evidence for the occurrence of both field-induced and
zero-field superconducting instabilities. Additionally, magnetization M(T,H) measurements suggest the occurrence of Fermi surface instabilities which compete with the superconducting correlations.
Fiz. Tverd. Tela (St. Petersburg) 41, 2135–2138 (December 1999) 相似文献
7.
E. A. Shapoval 《JETP Letters》1999,69(8):577-583
The lower critical field H
c1
cyl
(T) of a superconducting cylinder with radius r
0∼ξ(T)≪λ(T) is found on the basis of the Ginzburg-Landau theory with various boundary conditions. These results together with the well-known
results for the upper critical field are used to construct phase diagrams in terms of the field versus the reduced radius
r
0∼ξ(T) variables. The jump in the average magnetization at H
c1
cyl
(T) is calculated as a function of the reduced radius.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 8, 537–542 (25 April 1999) 相似文献
8.
N. N. Efimova M. B. Ustimenkova 《Journal of Experimental and Theoretical Physics》1998,87(6):1122-1128
In connection with the problem of identifying magnetic states in the vicinity of x
0 (the multicritical point of the x-T diagrams of spin-glass systems) a study has been made of properties that can be exploited to determine the presence of a
thermodynamic phase transition at the Curie point T
C and the distinctive features of the transition, specifically, the temperature dependence of the magnetic part of the specific
heat C
m(T), the temperature dependence of the low-field magnetization σ
H(T), and (with a view toward examining critical behavior in a magnetic field) the magnetization isotherms σ
H(T). The investigated object is the system of dilute ferrimagnetic spinels Li0.5Fe2.5−x
GaxO4, in which every type of magnetic state has spatially inhomogeneous cluster structures. The results obtained for a sample
with x=1.45 indicate that the classical criteria of a ferrimagnetic second-order phase transition at T
C=(97±2) K occur for x∼x
0. The results of similar investigations for a sample with x=1.6, which exists in the cluster spin-glass state for T<T
f=22 K and in an uncorrelated cluster state of the superparamagnetic type for T>T
f, are also given for comparison with the preceding case.
Zh. éksp. Teor. Fiz. 114, 2065–2077 (December 1998) 相似文献
9.
N. N. Efimova 《JETP Letters》1998,67(5):346-351
It is established on the basis of an investigation of the temperature dependences of the saturation magnetization σS(T) and the magnetic contribution to the specific heat C
m(T) that in the reentrant region of the x-T diagram (0.9⩽x⩽1.5) of dilute iron spinels Li0.5Fe2.5− x
GaxO4 there exists between the line of Curie points T
C(x) and the line of freezing temperatures T
f(x) another line of first-order phase transitions T
1(x) to a noncollinear ferrimagnetic phase: T
C(x)⩽T
1(x)⩽T
f(x).
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 329–333 (10 March 1998) 相似文献
10.
Summary It is shown that the behaviour of the temperature dependence of the critical current in polycrystalline thin films of high-T
c superconductors depends crucially on the assumption made concerning the nature of the intergranular material. The usual assumption
of a superconductor-insulator-superconductor (=SIS) ?sandwich? between each grain leads to a crossover fromI
c∼(1−T/T
c) toI
c∼(1−T/T
c)3/2, for temperatures nearT
c (whereI
c is the critical current,T the absolute temperature, andT
c the superconducting transition temperature). Instead, for a superconductor-normal metal-superconductor (=SNS) sandwich the
dependenceI
c∼(1−T/T
c)2 is found for all temperatures. Consideration is given to the effect of self-magnetic field on the analysis. The comparison
between expressions for continuous and granular systems is extended.
Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction. 相似文献
11.
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
12.
V. D. Blank V. M. Levin V. M. Prokhorov S. G. Buga G. A. Dubitskii N. R. Serebryanaya 《Journal of Experimental and Theoretical Physics》1998,87(4):741-746
The elastic properties of C60 fullerite samples synthesized under pressure P=13.0 GPa at high temperatures were investigated using acoustic microscopy. The velocities of longitudinal (c
L=17–26 km/s) and transverse (c
T=7.2–9.6 km/s) elastic waves in the samples were measured. It was established that the longitudinal sound velocity of ultrahard
fullerites is higher than that of any other known solid. The bulk modulus of these ultrahard samples is higher than that of
diamond and reaches a value greater than 1 TPa. The high bulk modulus, the relatively large shear moduli, and the substantial
Poisson ratio indicate that the structure of the ultrahard fullerites is fundamentally different from that of diamond.
Zh. éksp. Teor. Fiz. 114, 1365–1374 (October 1998) 相似文献
13.
It is inferred from the position of the 2Δ peak in the electron light scattering spectra that in a sample with high T
c
≈90 K the ratio 2Δ/T
c
is approximately equal to 6 and 7 for different polarizations, while in overdoped samples with T
c
≈40 and 35 K the 2Δ peak is observed only in x′y′ polarization with a substantially lower ratio 2Δ/T
c
≈3.2. With decreasing T
c
in Tl2Ba2CuO6+x
crystals, a transition occurs from strong to weak coupling; the superconducting gap remains anisotropic at different doping
levels.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 11, 760–765 (10 December 1996) 相似文献
14.
M. I. Petrov D. A. Balaev K. A. Shaikhutdinov K. S. Aleksandrov 《Physics of the Solid State》1999,41(6):881-886
Measurements of the temperature dependence of the electrical resistance R(T) below the superconducting transition temperature have been performed at different values of the transport current in HTSC+CuO
composites modeling a network of weak S-I-S Josephson junctions (S—superconductor, I—insulator). It has been shown experimentally that the temperature dependence R(T) at different values of the transport current is adequately described by means of the mechanism of thermally activated phase
slippage developed by Ambegaokar and Halperin for tunnel structures. Within the framework of this model we have numerically
calculated the temperature dependence of the critical current J
c(T) as defined by various criteria. Qualitative agreement obtains between the measured and calculated temperature dependences
J
c(T).
Fiz. Tverd. Tela (St. Petersburg) 41, 969–974 (June 1999) 相似文献
15.
The effect of γ irradiation on the temperature hysteresis in dielectric permittivity ɛ and loss tangent tan δ of crystalline Rb2ZnBr4 has been studied in the vicinity of the incommensurate-commensurate phase transition. The ɛ(T) and tan δ(T) curves were found to exhibit anomalies in the form of maxima. Hysteresis was observed in the measured properties, including
the transition temperature T
c
(ΔT=T
c
h
−T
c
c
), in both unirradiated and irradiated samples. It is shown that, as the radiation dose increases the extent of the hysteresis
ΔT increases, the values of ɛ
max and tan δ
max at the transition point decrease, and the anomalies wash out.
Fiz. Tverd. Tela (St. Petersburg) 40, 1911–1914 (October 1998) 相似文献
16.
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
17.
Z. V. Golubenko L. P. Ol’khovik Yu. A. Popkov Z. I. Sizova A. S. Kamzin 《Physics of the Solid State》1998,40(10):1718-1720
The anisotropy of a system of barium ferrite particles with an average diameter of 60 nm has been studied. The effective anisotropy
constant has been determined in the temperature range from 4.2 K to T
c by the law governing approach to saturation magnetization. The observed deviation from the magnetocrystalline anisotropy
constant is explained as due to a negative contribution of the “surface” anisotropy constant. An estimate is made of this
contribution as a function of particle size.
Fiz. Tverd. Tela (St. Petersburg) 40, 1894–1897 (October 1998) 相似文献
18.
Alexander Cigáň Gustav Plesch Martin ?krátek Michal Kop?ok Ján Maňka Peter Jurdák Anton Koňakovsky 《Central European Journal of Physics》2011,9(1):213-221
Bulk samples of the nominal composition of (Tl0.6Pb0.5)(Sr0.8Ba0.2)2Ca2Cu3O8+δ−xLaO1.5 (x = 0–0.1) were prepared by using two-step process and their microstructure, T
c
values, and magnetization were studied. The samples consist of the Tl-1223 dominant phase with small Tl-1212 admixture, which
increases with a rise of La content. Five years ageing and following oxygen annealing at 450°C and subsequently at 750°C have
only a modest effect on T
c
values of the studied samples. Low-level La doping (x = 0:04) leads to an increase of T
c
values by about 2 K in comparison with undoped samples. Oxygen annealing at 750°C results in an increase in the volume magnetization
hysteresis in low applied magnetic fields and rise of critical current density at zero magnetic field and 77 K. This effect
is most pronounced for the low La doped sample with x = 0.04. Changes of the induced voltage, U originating in the Meissner effect and of its harmonics in dependence on temperature were measured and used for characterization
of the temperature distribution of inter-grain junctions. 相似文献
19.
Spinal ferrites having the general formula Co1 − x
Zn
x
Fe2 − x
Al
x
O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were prepared using the wet chemical co-operation technique. The samples were annealed
at 800°C for 12 h and were studied by means of X-ray diffraction, magnetization and low field AC susceptibility measurements.
The X-ray analysis showed that all the samples had single-phase cubic spinel structure. The variation of lattice constant
with Zn and Al concentration deviates from Vegard’s law. The saturation magnetization σ
s and magneton number n
B measured at 300 K using high field hysteresis loop technique decreases with increasing x, suggesting decrease in ferrimagnetic behaviour. Curie temperature T
C deduced from AC susceptibility data decreases with x, suggesting a decrease in ferrimagnetic behaviour.
相似文献
20.
V. F. Gantmakher G. E. Tsydynzhapov L. P. Kozeeva A. N. Lavrov 《Journal of Experimental and Theoretical Physics》1999,88(1):148-156
A superconducting transition in the temperature dependence of the ab-plane resistivity of underdoped YBa2Cu3O6+x
crystals in the range T
c≲30 K has been investigated. Unlike the case of samples with the optimal level of doping, the transition width increased insignificantly
with magnetic field, and in the range T≲13 K it decreased with increasing magnetic field. The transition point T
c(B) was determined by analyzing the fluctuation conductivity. The curves of B
c2(T) measured in the region T/T
c≳0.1 did not show a tendency to saturation and had a positive second derivative everywhere, including the immediate neighborhood
of T
c. The only difference among the curves of B
c2(T) for different crystal states is the scales of Tand B, so they can be described in terms of a universal function, which fairly closely follows Alexandrov’s model of boson superconductivity.
Zh. éksp. Teor. Fiz. 115, 268–284 (January 1999) 相似文献