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1.
A. Weidinger Ch. Niedermayer H. Glückler A. Golnik G. Nowitzke E. Recknagel H. Eickenbusch W. Paulus R. Schöllhorn J. I. Budnick 《Hyperfine Interactions》1991,63(1-4):147-153
Oxygen-deficient YBa2Cu3O6+x
samples were investigated by the muon spin rotation technique in zero external field. In an intermediate oxygen concentration
region we find strongly relaxing μSR signals indicating the existence of internal magnetic fields. The strongly relaxing signals
were observed only in samples with superconducting transition temperatures below 50 K. As an interpretation of the data we
suggest that magnetic ordering and superconductivity coexist in these samples within regions of extensions of a few lattice
constants, but not necessarily on the same sites. 相似文献
2.
Possible positive muon sites in YBa2Cu3O
x
were determined from the observedμ
+ hyperfine fields in antiferromagnetically ordered YBa2Cu3O
x
and GdBa2Cu3O7. After determining theμ
+ sites, the possibility of anyons or chiral spin ordering in the superconducting YBa2Cu3O7 is discussed. Positive muon implanted in YBa2Cu3O7 feel static magnetic fields of average 1.4G, which are explicable in terms of nuclear magnetic dipolar fields. Non observation
of static local magnetic fields of electronic origin (the upper limit is the order of 0.1 G) means that anyons or chiral spin
ordering might not exist in superconducting YBa2Cu3O7. 相似文献
3.
L. G. Mamsurova K. S. Pigalskiy N. G. Trusevich N. B. Butko A. A. Vishnev 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(8):1086-1089
We study the reasons for which the compound YBa2Cu3O
y
begins to lose its superconducting ability with a decrease in particle sizes to values of ∼0.1 μm. Our analysis of the results
of structural and magnetic studies has allowed us to reveal changes in the parameters of the crystal structure and of the
superconducting state in small particles of an HTSC and to show that the main cause of these changes is a special kind of
a structural disorder peculiar only to small particles of YBa2Cu3O
y
and is realized as a consequence of the need for nonequilibrium conditions during their synthesis. 相似文献
4.
T. M. Riseman J. H. Brewer E. J. Ansaldo P. M. Grant M. E. Lopez-Morales B. M. Sternlieb 《Hyperfine Interactions》1991,63(1-4):249-252
Zero and weak transverse fieldμ
+ SR measurements on PrBa2Cu3O
x
samples withx≈6 andx≈7 show ordered magnetism in both oxygen concentration limits. As expected for equivalent doping (nominally PrBa2Cu3O
x
∼YBa2Cu3O
x
−0.5), neither sample is superconducting. Two muon signals are observed in thex≈6 sample, as in YBa2Cu3O6, but only one (the weaker) has the same local magnetic field as in YBa2Cu3O6. In thex≈7 sample, only one site is observed; its local field is reduced with respect to that of the primary site in YBa2Cu3O6 by a factor roughly consistent with the carrier-density dependence of the Cu ion moment in antiferromagnetic YBa2Cu3O
x
. 相似文献
5.
V. É. Gasumyants E. V. Vladimirskaya M. V. Elizarova I. B. Patrina 《Physics of the Solid State》1999,41(3):350-354
Temperature dependences of the resistivity and Seebeck coefficient of Y(Ba1−x
Lax)2Cu3Oy and YBa2Cu3−x
CoxOy samples (x=0–0.25) have been measured under maximum sample saturation with oxygen, as well as following their anneal in an oxygen-deficient
atmosphere. The T
c (x) dependences for as-prepared samples were found to pass through a maximum at x=0.05, which persists after annealing for Y(Ba1−xLax)2Cu3Oy and disappears for YBa2Cu3−x
CoxOy. A phenomenological model of the band spectrum in normal phase has been used to determine the parameters of the conduction
band and of the carrier system, and to analyze their variation with the dopant type and content, as well as with annealing.
Despite the differences observed in the T
c (x) dependence, the critical temperatures for all the sample series studied were found to correlate with the conduction-band
effective width. The mechanism of the effect of impurities on the band-structure parameters and the reasons for the different
influence of annealing on the properties of Y(Ba1−x
Lax)2Cu3Oy and YBa2Cu3−x
CoxOy are discussed.
Fiz. Tverd. Tela (St. Petersburg) 41, 389–394 (March 1997) 相似文献
6.
S. Okuma H. Miyatake N. Nishida Y. Ueda S. Katsuyama K. Kosuge J. H. Brewer 《Hyperfine Interactions》1991,63(1-4):265-270b
Spin-glass like magnetic ordering of iron moments was observed in both orthorhombic and tetragonal YBa2(Cu1−xFex)3Oy (x=0.08) by μ+SR measurements. In a “Tetra” sample, all the muons sense the superconducting transition at 60 K and magnetic ordering at
around 15 K, while in an “Ortho” sample they reveal that two magnetically different parts exist in the sample: about 40% of
the sample is superconducting withT
c
≈90K and the remaining part is magnetic withT
M≈33K. These phenomena can be explained in terms of clustering of the Fe atoms in the “Ortho” sample. 相似文献
7.
A. M. Balagurov L. G. Mamsurova I. A. Bobrikov To Thanh Loan V. Yu. Pomjakushin K. S. Pigalskiy N. G. Trusevich A. A. Vishnev 《Journal of Experimental and Theoretical Physics》2012,114(6):1001-1011
The atomic structure of YBa2Cu3O y fine-crystalline HTSC samples with various average crystallite sizes ??D?? ranging from 0.4 to 2 ??m and an oxygen concentration y close to the optimal value for superconductivity (y ?? 6.93) is investigated by the neutron diffraction technique. We have found some effects associated with the redistribution of cations and oxygen atoms and with variations in the positions of atomic layers in the unit cell, which are not observed in macrocrystalline samples. In all probability, these effects appear due to nonequilibrium conditions of synthesis required for obtaining this compound in the fine-crystalline state. The results have made it possible to explain the peculiar physical properties of fine-crystalline YBa2Cu3O y samples (in particular, the coexistence of high superconducting transition temperatures T c and noticeably lower values of magnetization in strong magnetic fields for T < T c ). It is shown that a nanoscale structural inhomogeneity exists in fine-crystalline YBa2Cu3O y samples with the optimal oxygen content and changes the fundamental superconducting parameters, viz., the magnetic field penetration depth and the coherence length. 相似文献
8.
L. G. Mamsurova N. G. Trusevich K. S. Pigalskiy N. B. Butko A. A. Vishnev 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1136-1139
It was proven experimentally that the structural disordering inherent to fine-grained high-temper- ature YBa2Cu3O
y
superconductors (with an average grain size of 〈D〉 < 2 μm) leads to a reduction of the level of hole doping and the creation of features inherent to the pseudogap state (antiferromagnetic
correlations and the lowered density of states at the Fermi level) even in samples with optimum oxygen content y ≈ 6.92. 相似文献
9.
M. D. Lan J. Z. Liu R. N. Shelton 《Applied Physics A: Materials Science & Processing》1993,56(4):381-384
The zero-field-cooled magnetization relaxation has been studied over wide temperature and field ranges on iron-doped YBa2Cu3O7–y
single crystals. The relationship between the twin boundary density, which depends on the iron composition, and the pinning strength of the flux lines is determined systematically. For magnetic fields up to 1 T the inductive critical current density decreases as the iron composition increases. The Bean critical state model and the Anderson-Kim thermally activated flux-creep model are utilized to analyze and interpret the experimental results. 相似文献
10.
W. J. Kossler X. H. Yu A. Greer H. E. Schone C. E. Stronach M. Davis R. S. Cary J. E. Crow W. F. Lankford J. Oostens 《Hyperfine Interactions》1991,63(1-4):81-86
Transverse and zero-field μSR measurements were made on YBa2(Cu1−xNix)3O7−y withx=0.1 and 0.2, and YBa2(Cu1−x
Zn
x
)3O7−y
withx=0.03, 0.06, 0.1, and 0.16, wherey≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence
was found over the temperature range studied: 10–100 K. However, depolarization rates as functions of temperature were obtained,
and the low temperature values of these are σ=3.2 μs−1.1.6μs−1, and 1 μs−1 forx=0.01, and 0.2 Ni, respectively, and σ=0.8 μs−1, 0.75 μs−1, 0.65 μs−1, and 0.4 μs−1 forx=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made,
but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction
in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the
relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect
of scattering. 相似文献
11.
Magnetic behavior of Fe atoms in YBa2(Cu1−x
Fe
x
)3O
y
system in superconducting (SC) and non-SC states is studied. In SC region one magnetic ordering point Tm1 is observed for all Fe atoms in Cu1 sites: Tm1=10 K and 16 K for x=0.05 and x=0.10, respectively. In the non-SC state for x=0.05 Cu1 and Cu2 sublattices are magnetically
independent and two magnetic ordering points are found: Tm1=20 K and Tm2=405K. For x=0.10 a strong magnetic interaction between Cu1 and Cu2 sublattices appears and only one ordering point Tm2=435 K is observed. 相似文献
12.
S. G. Barsov A. L. Getalov V. P. Koptev L. A. Kuzmin S. M. Mikirtychyants G. V. Scherbakov A. A. Vasiljev V. K. Fedotov V. I. Kulakov R. K. Nicolaev N. S. Sidorov Y. M. Mukovskii A. S. Nigmatulin S. E. Strunin 《Hyperfine Interactions》1991,63(1-4):161-167
In this work the magnetic and superconducting properties of YBa2Cu3O6+x
, ceramic samples are studied with regard to there preparations technology and oxygen content. It is shown that at 0.41≤x≤0.45 the magnetic and superconducting states coexist. 相似文献
13.
The temperature dependences of the resistivity and of the Seebeck coefficient S is studied in three series of Y1−x
CaxBa2Cu3−x
CoxOy samples (x=0–0.3) differing in oxygen content. It was found that the critical temperature decreases for y≈7.0, and S(T=300 K) increases with doping, whereas oxygen deficiency results in a nonmonotonic variation of these quantities with increasing
x. The band structure parameters have been determined from an analysis of the S(T) relations using a phenomenological theory of electron transport. It was found that an increase in x results in a gradual increase in band asymmetry, which is caused by calcium-induced creation of additional states in the
band responsible for conduction in the normal phase. An analysis has shown that high impurity concentrations in oxygen-deficient
Y1−x
CaxBa2Cu3−x
CoxOy samples bring about an additional ordering of the structure, which may be caused by formation of a cobalt superlattice. It
has also been shown that, in the case of Ca and Co codoping, the dependence of critical temperature on effective conduction-band
width coincides with the universal correlation relation observed in the YBa2Cu3Oy system with single substitutions in various lattice sites.
Fiz. Tverd. Tela (St. Petersburg) 41, 1363–1371 (August 1999) 相似文献
14.
The nonlinear magnetic properties of YBa2Cu3O7 − x
high-temperature superconducting polycrystals are investigated. Using the results of investigations as a basis, a method
for controlling the amplitudes of generated magnetization harmonics is worked out and a controllable harmonic generator is
devised. The amplitudes of the harmonics are controlled by means of a permanent magnetic field or current. The use of YBa2Cu3O7 − x
polycrystals makes it possible to produce a spectrum with offering a large number of higher harmonics. An YBa2Cu3O7 − x
-based device has a wide dynamic range; its design is simple and reliable in a wide interval of the amplitudes of an input
signal. 相似文献
15.
Parshant Batham S B Roy Shailendra Kumar A K Pradhan A K Grover P Chaddah Ram Prasad N C Soni 《Pramana》1995,45(3):261-269
Results are presented for study of nonlinear magnetization of a sintered YBa2Cu3O7−y pellet of different thickness of a sample subjected to very low magnetic field. On cooling the sample belowT
c in zero field a change, in the oscillatory structure of harmonics in increasing dc field is observed in very low ac magnetic
field. The effect of finiteness of the sample on the oscillatory structure and on the hysteresis of harmonics is also studied.
The results are explained qualitatively. 相似文献
16.
E. Karlsson C. A. Chatzidimitriou-Dreismann E. J. Brändas 《Hyperfine Interactions》1991,66(1-4):373-379
Fullyc-axis oriented thin films of YBa2(Cu1−x
57Fe
x
)3O7−y
were studied by varying the Fe- and O-content and the substrate. For the two substrates MgO and SrTiO3 no difference in the CEMS spectra was observed. Measurements for differentx andy values and their comparison with results from powder samples proved that the solubility of iron is the same in the films
and powders. The substitution of Cu(2) by Fe in the films is the highest ever reported. The CEMS spectrum of a reduced film
shows that the direction of the magnetic hyperfine field for doubletC is perpendicular to thec-axis. 相似文献
17.
《Journal of Physics and Chemistry of Solids》2001,62(9-10):1837-1846
We report the transport studies of YBa2Cu3Oy/YxPr1−xBa2Cu3Oy and YBa2Cu3Oy/R1−xMxMnO3 superlattices in magnetic fields in which R=La or Nd, and M=Ca or Sr. The X-ray diffraction of samples shows superlattice structure. The resistive transition in a magnetic field shows thermal activated behavior. The flux pinning is reduced when the coupling strength between YBCO layers is decreased. The angular dependence of the critical current of YBa2Cu3Oy/PrBa2Cu3Oy superlattices reveals the dimensionality of superlattices. The magnetoresistance ratio (MR), |Δρ(H=7 T)−Δρ(H=0)|/Δρ(H=7 T), of YBa2Cu3Oy/R1−xMxMnO3 superlattices is affected by the layer coupling of R1−xMxMnO3 layers. The enhancement of the MR ratio in the tri-layer YBa2Cu3Oy/La0.7M0.3MnO3/YBa2Cu3Oy film in the low temperature regime is significant and has a value of 33650% at T=75 K. We attribute this enhancement of the MR to the ordering of magnetic moment in ferromagnetic layers in magnetic fields. The results are discussed in terms of existing theories. 相似文献
18.
W. K. Dawson C. H. Halim S. P. Weathersby J. A. Flint J. C. Lam T. J. Hoffman C. Boekema KC. B. Chan R. L. Lichti D. W. Cooke M. S. Jahan J. E. Crow 《Hyperfine Interactions》1991,63(1-4):219-226
Key results of zero-field (ZF) and transverse-field (TF) muon-spin-relaxation (μSR) experiments on superconducting and insulating
RBa2Cu3O
y
(R123
y
, with R=Eu, Gd, Pr and Pr/Y:y=6, 7) are examined. The chemical behavior of the positive muon probe is addressed, and muon-oxygen bonding is shown to occur
in all these cuprates. To explain magnetic fields at muon-probe sites in Pr
x
Y1−x
Ba2Cu3O
y
(0<=x<0.5,y=7 andx=0,y=6) samples, improvements on the reported magnetic structures from neutron diffraction are necessary. Cu magnetism in Pr123y (y=6,7) is observed belowT
N1, which is near RT. The magnetism seen belowT
N2 can be interpreted assuming an additional ordering in the Cutt-O chain layers. Alternatively, Pr ordering is also considered
as the cause of the second phase transition. Considering the specific muon-probe location, a more detailed interpretation
can be provided for the μSR parameters, measured in the normal and mixed states of these unconventional superconductors. 相似文献
19.
Zhao Min-Guan Zhao Xiao-Ning Zeng Xiao-Lan 《Zeitschrift für Physik B Condensed Matter》1988,72(3):353-355
Various superconductivity mechanisms show that the electron pair is in spin singlet (S=0) belowTc. In contrast with these, our EPR measurements show that the electron pair is in spin triplet (S=1) rather than the spin singlet. Since an intense zero field absorption was observed in the high temperature superconductors of YBa2Cu3O7–y
, and YBa2Cu3O7–y
F1, which violated various spin-pairing singlet superconductivity mechanisms. 相似文献
20.
The thermopower in the YBa2−x
LaxCu3Oy system (x=0–0.5) has been studied. An analysis made in terms of the narrow-band model revealed trends in the variation of the main
band parameters with increasing lanthanum concentration. The dependence of the conduction band width on lanthanum concentration
was found to pass through a weak minimum at x=0.05–0.1, which correlates in position with the maximum in the concentration dependences of the critical temperature and
degree of sample orthorhombicity. The results obtained and their comparison with Fe, Co→Cu substitution data permit a conclusion
that the main factor affecting the properties of the YBa2Cu3Oy system under nonisovalent substitution of various cations is the increasing disorder in the chain-oxygen subsystem caused
by increasing impurity content.
Fiz. Tverd. Tela (St. Petersburg) 40, 17–22 (January 1998) 相似文献