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  • 1
    Electronic Resource
    Electronic Resource
    Inhomogeneity of Charge and Spin Distribution in CuO2 Layers of High-Tc Superconductors: NQR/NMR Studies of 1-2-3 Compounds (1999)
    Springer
    Journal of superconductivity 12 (1999), S. 113-115 
    Details
    ISSN: 1572-9605
    Keywords: CuO2 layers ; NQR ; ZFNMR ; spin-lattice relaxation ; chain fragments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The copper NQR and ZFNMR and thulium NMR are studied in a series of 123 superconductors. It is found that in the aged 60-K superconductors RBa2Cu3O6+x the well known conducting (nonmagnetic) phase co-exists with the magnetically-ordered phase. Both microphases contain two types of inequivalent Cu(2) sites in CuO2 planes. In the conducting phase, these sites differ only in the Cu(2) NQR frequency, whereas in the magnetic one they differ also in the value of hyperfine magnetic fields at Cu(2) nuclei. These differences and the occupation numbers of the two sites are found to be independent of x (in the range x=0.5÷0.6) and of the volume fraction of the magnetic phase. At low temperatures, the nuclear spin-lattice relaxation in both microphases proceeds via magnetic centers formed by hole-doped Cu–O–Cu chain fragments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007742224387
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic phase separation in TmBa2Cu4O8 (1996)
    Springer
    JETP letters 63 (1996), S. 227-233 
    Details
    ISSN: 1090-6487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The NQR spectra of Cu(2) in the superconductor TmBa2Cu4O8 are studied at temperatures from 300 to 4.2 K. In analyzing the spectra it is assumed that the NQR line of each isotope contains two Gaussian components — narrow (n) and broad (b). It is discovered that the NQR frequencies have a minimum at the temperature T*=150 K. The frequencies of the components of the spectrum are close at temperatures from T* to 4.2 K and differ substantially at temperatures T〉T*. Both components are broadened as the temperature decreases, but this broadening occurs especially rapidly at temperatures T〈T*. The relative intensity of the narrow component I n/(I n+I b) equals 1/6 for T=225−160 K, increases abruptly at T=T*, and remains constant (1/3) at temperatures T from 125 to 4.2 K. Analysis of the experimental data showed that the anomalous temperature dependences of the Cu(2) NQR spectra could be due to electronic phase separation (stratification) in the CuO2 planes at temperatures T⩽T*.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.566995
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  • 3
    Electronic Resource
    Electronic Resource
    Shape of the Cu(2) NQR spectra in YBa2Cu3O7, TmBa2Cu3O7 and TmBa2Cu4O8 (1997)
    Springer
    JETP letters 66 (1997), S. 624-629 
    Details
    ISSN: 1090-6487
    Keywords: 76.60.Gv ; 74.72.Bk ; 74.72.Yg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a study of shape of the Cu(2) NQR spectra in YBa2Cu3O7, TmBa2Cum3O7, and TmBa2Cu4O8 compounds at temperatures of 4.2–300 K. The results of the quantitative analysis lead us to conclude that the shape of the Cu(2) NQR spectra in all the samples studied can be described in the framework of the “motional narrowing” model, which implies that the Cu(2) nucleus possesses two different NQR frequencies between which it can rapidly jump. The difference in frequencies seems to be related to the charge-stripe correlations in CuO2 planes resulting in a dynamical modulation of the electric field gradients at the Cu(2) nuclei.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567612
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  • 4
    Electronic Resource
    Electronic Resource
    Stripe motion in CuO2 planes of Y1−x Pr x Ba2Cu3O7 as observed from the Cu(2) quadrupole resonance (1997)
    Springer
    JETP letters 65 (1997), S. 821-827 
    Details
    ISSN: 1090-6487
    Keywords: 61.72.Hh ; 74.72.Bk ; 74.80.−g ; 76.60.Gv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567452
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  • 5
    Electronic Resource
    Electronic Resource
    Comparative studies of the NMR of thulium in Tm123 and Tm124 compounds: Evidence for structural and electronic phase separation (1996)
    Springer
    JETP letters 64 (1996), S. 398-403 
    Details
    ISSN: 1090-6487
    Keywords: 61.72.Hh ; 74.72.Bk ; 74.80.Bj ; 76.60.Lz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The nuclear magnetic relaxation of 169Tm in TmBa2Cu3O6+x (x=0.1–1.0, Δ x=0.1) and TmBa2Cu4O8 is studied at temperatures below 5 K. In all the samples, the Tm spin-lattice relaxation proceeds via intrinsic paramagnetic centers (PCs) like Cu2+ or copper-oxygen spin-polarized clusters. The experimental data for TmBa2Cu3O6+x support the idea of the structural (chemical) micro-phase separation in oxygen-deficient 123 compounds. Apparently, the samples with x⩾0.4 contain hole-poor nonsuperconducting regions, enriched with PCs, and hole-rich (PC-poor) superconducting regions. The volume fraction f n of the PC-rich phase reaches a maximum value of 0.85 at x=0.4 and decreases monotonically with increasing x (f n=0.5, 0.3, and 0.25 at x=0.5, 0.6, and 0.7, respectively). The Tm spin-lattice relaxation in the underdoped TmBa2Cu4O8 compound indicates that this sample, in contrast to oxygen-deficient TmBa2Cu3O6+x , has a homogeneous composition. However, the Tm spin-spin relaxation measurements reveal two sorts of the Tm nuclear spins in Tm124, having different NMR spectra and different relaxation times T 2. The latter result is evidence of electronic phase separation in CuO2 phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567210
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  • 6
    Electronic Resource
    Electronic Resource
    Nuclear magnetic relaxation in rare-earth compound crystals due to fluctuations of hyperfine magnetic fields (1990)
    Springer
    Hyperfine interactions 59 (1990), S. 255-270 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Some results on NMR and relaxation studies of the Van Vleck paramagnet TmES (thulium ethylsulphate) and the Ising ferromagnet DyES are summarized. Complicated but regular quasistatic internal magnetic fields are created by Tm and Dy ions in these compounds. These fields fluctuate due to the thermal excitation of tne ions and the energy transfer from one ion to another. Fluctuations give rise to NMR line shifts, broadening of the lines and spin-lattice relaxation, the shifts, linewidth and spin-lattice relaxation rate being proportional to exp(−Δ/kT) at low temperatures (kT≪Δ, Δ is an excitation energy). Pre-exponential factors depend on fluctuating fields in a definite but complicated manner, so estimates of the correlation time (electron spin-spin relaxation time) can be obtained from measurements of nuclear relaxation rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02401226
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  • 7
    Electronic Resource
    Electronic Resource
    Intrinsic paramagnetic centers in 1-2-3 superconductors (1995)
    Springer
    Journal of superconductivity 8 (1995), S. 413-416 
    Details
    ISSN: 1572-9605
    Keywords: 1-2-3 superconductors ; NMR ; NQR ; spin-lattice relaxation ; paramagnetic centers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00722818
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