Singlet-ground-state paramagnetic centers in CuO2 layers as seen from Tm169 NMR in TmBa2Cu3O6+x superconductors

The Tm169 nuclear spin-lattice relaxation in oxygen-deficient TmBa2Cu3O6+x compounds, as quenched and room-temperature annealed, has been measured at low temperatures. The results are consistent with the existence of paramagnetic centers in the CuO2 double layer, which have a nonmagnetic (singlet) ground state separated from an excited magnetic state by an energy gap of the order of 1 K. © 1995 The American Physical Society

Stripe motion in CuO2 planes of Y1-xPrxBa2Cu3O7 as observed from the Cu(2) quadrupole resonance

The NQR spectra of copper in the compounds YBa2Cu3O7, TmBa2Cu3O7, and Y0.9Pr0.1Ba2Cu3O7 at temperatures of 4.2-200 K are investigated by a pulsed NQR technique at frequencies of 28-33 MHz. Quantitative analysis of the spectra shows that the shape of the "plane" Cu(2) spectra is well described by using a model of 1D correlations of the charge and spin distribution in the CuO2 planes (stripe correlations). In the undoped superconductors the charge-spin stripe structure moves fast in the CuO2 planes, but doping the YBa2Cu3O7 lattice with praseodymium slows this motion down. © 1997 American Institute of Physics

Cu(2) nuclear resonance evidence for an original magnetic phase in aged 60K-superconductors RBa2Cu3O6+x (R=Tm,Y)

It is widely believed that the long-range antiferromagnetic order in the RBa2Cu3O6+x compounds (R=Y and rare earths except of Ce, Pr, Tb) is totally suppressed for the oxygen index x>0.4 (AFM insulator-metal transition). We present the results of the copper NQR/NMR studies of aged RBa2Cu3O6+x (R=Tm,Y) samples showing that a magnetic order can still be present at oxygen contents x up to at least 0.7 and at temperatures as high as 77K.Comment: 7 pages, 6 figures. Submitted to Phys.Rev.

Cu(2) nuclear resonance evidence for a magnetic phase in aged 60-K superconductors RBa2Cu3O6+x (R = Tm, Y)

It is widely believed that the long-range antiferromagnetic order in the RBa2Cu3O6+x compounds (R = Y and rare earths except for Ce, Pr, Tb) is totally suppressed for the oxygen index x ≥ 0.4 (antiferromagnetic insulator-metal transition). We present the results of the copper nuclear quadrupole resonance/NMR studies of aged RBa2Cu3O6+x (R = Tm, Y) samples showing that a magnetic order can still be present at oxygen contents x up to at least 0.7 and at temperatures as high as 77 K

Intrinsic paramagnetic centers in 1-2-3 superconductors

The169Tm "enhanced" NMR in TmBa2Cu3O6+x (x=0.5, 0.6) at temperatures below 4.2K and the63Cu(1) NQR in YBa2Cu3O6.5 at temperatures above 4.2K are used to study properties of intrinsic paramagnetic centers incorporated into superconducting materials. The spin-lattice relaxation of thulium and copper nuclei reveals three types of paramagnetic centers to be present in oxygen-deficient 1-2-3 superconductors, those are (1) two-level ones with a spin S=1/2, localized outside CuO2 bilayers, (2) singlet-ground-state paramagnetic centers with an integer spin S≥1 in CuO2 bilayers, and (3) exchange copper-oxygen clusters with a half-integer spin S≥5/2, localized in a nearest neighborhood of CuOx basal plane at boundaries of superconducting OrthoII microdomains. © 1995 Plenum Publishing Corporation

Intrinsic magnetic centers and microdomains in oxygen-deficient YBa2Cu3O6.5 and TmBa2Cu3O6+x

We measured the influence of magnetic centers (MC's) on the nuclear relaxation in 123 compounds using 169Tm NMR and 63Cu NQR in TmBa2Cu3O6+x (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6), and 89Y NMR and 63Cu NQR in YBa2Cu3O65. Particular attention is paid to the region 0.5≤x≤0.6 in order to deal with both a well-defined ortho II structure and a high enough MC concentration. The experiments reveal a two-component nuclear relaxation in the superconducting compounds at temperatures above 1 K, especially pronounced in the x = 0.5 samples. The relaxation data give evidence for microphase separation due to oxygen disorder in the basal CuOx planes. In the well-annealed samples, the MC's predominating the relaxation have S= 1/2. The concentrations of these MC's are of the order of 3% in the disordered (nonsuperconducting) microphase and ∼0.3% in the ordered (superconducting) one

Клинический случай генерализованного врожденного токсоплазмоза

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Electronic structure and lattice dynamics of domeykite CU3As according to nuclear quadrupolar resonance of 75As and 63,65CU

The temperature dependences of nuclear quadrupole resonance (NQR) frequencies, the line width and nuclear relaxation of 75As and 63,65Cu, as well as the electrical resistivity in domeykite Cu3As are studied in the temperature range of 4.2-300 K. The comparison of the calculated with the measured lattice contribution to the NQR frequencies points at a substantial role played by the conduction electrons in creating the electric field gradient at the nuclei sites. The temperature dependence of the copper and arsenic nuclear spin-lattice relaxation linear at 4.2 < T < 200 K and that of the electric resistivity (30 < T < 200 K) prove the metallic character of the conductivity of domeykite. The enhancement of nuclear relaxation, the narrowing of copper and arsenic NQR line widths are considered as arising due to the ionic movement starting beyond 200 K. This movement influences the electric resistivity, most likely due to the inreasing density of states at the Fermi surface

Stripe motion in CuO2 planes of Y1-xPrxBa2Cu3O7 as observed from the Cu(2) quadrupole resonance

The NQR spectra of copper in the compounds YBa2Cu3O7, TmBa2Cu3O7, and Y0.9Pr0.1Ba2Cu3O7 at temperatures of 4.2-200 K are investigated by a pulsed NQR technique at frequencies of 28-33 MHz. Quantitative analysis of the spectra shows that the shape of the "plane" Cu(2) spectra is well described by using a model of 1D correlations of the charge and spin distribution in the CuO2 planes (stripe correlations). In the undoped superconductors the charge-spin stripe structure moves fast in the CuO2 planes, but doping the YBa2Cu3O7 lattice with praseodymium slows this motion down. © 1997 American Institute of Physics