A. Trokiner

71Ga and 69Ga nuclear magnetic resonance study of β-Ga2O3: resolution of four- and six-fold coordinated Ga sites in static conditions

71Ga and 69Ga nuclear magnetic resonance (NMR) spectra have been obtained for beta-Ga2O3 at magnetic fields of 11.7 and 7.0 T with a combination of static and spinning samples and using echo techniques. Isotropic chemical shifts and well constrained electric field gradient (EFG) tensors were measured for the GaIV and GaVI sites in beta-Ga2O3 and are reported for the first time. Due to its high quadrupolar coupling constant the GaIV site in beta-Ga2O3 is only resolved in static conditions. Analysis of spectral discontinuities obtained for different isotopes and magnetic field strengths and a method of readily obtaining very broad spectra without point by point acquisition demonstrate an approach that should be very useful in constraining the chemical shifts and quadrupole parameters involved in solid-state gallium NMR spectra.

207Pb and 17O NMR study of the electron density distribution in the metallic phase of BaPb1-xBixO3

The 17O and 207Pb NMR spectra were measured in ceramic samples in the metallic phase of BaPb_{1-x}Bi_{x}O_3 oxides (0<x<0.33). The inhomogeneous magnetic broadening which appears due to a distribution of the Knight shifts was analyzed in detail. It is shown that Bi atoms, which are randomly incorporated in BaPbO_3 parent compound give rise to an increased conduction electron spin density within an area which is delimited by its two first cation shells. According to NMR data the percolative overlap of these areas occurs in superconducting compositions and it is accompanied by a sharp growth of the average Knight shift<Ks>. The decrease of<17Ks>with temperature revealed for x=0.33 evidences for an opening of the energy gap near E_F near the metal-semiconductor transition (x=0.35).

NMR determination of the Sternheimer antishielding factor of Ca2

The experimental determination of the Sternheimer antishielding factor gamma(infinity) for Ca2+ in a sold material is reported for the first time. The gamma(infinity) value was obtained by comparing the quadrupole frequency measured by 43Ca NMR with the electric field gradient calculated in a frame of the point charge approximation in the high-Tc superconducting compound, Tl0.5Pb0.5Sr2CaCu2O7. The deduced value (gamma(infinity)= -6.1+/-.9) is about one-third of that obtained from the quantum mechanical calculations, whereas in the same sample, the gamma(infinity)value for O2- deduced by the same procedure (gamma(infinity)= -13.7+/-2.0) is very close to the calculated one.

17O NMR IN HIGH-TC SUPERCONDUCTOR TL2BA2CACU2OY

Abstract 17 O NMR measurements have been performed between 10 and 400 K on an overdoped sample of Tl 2 Ba 2 CaCu 2 O y ( T c = 103 K). The electric field gradient parameters were deduced for all the oxygen sites. The temperature dependence of the magnetic hyperfine shift was measured for all these sites. No thermal variation of the shift was detected down to T c for oxygen in the TlO reservoir plane. As for oxygen in the CuO 2 plane the temperature dependence of the shift is similar to that for 205 Tl NMR line from thallium defects in the Ca layer measured in the same powder sample. This similarity is consistent with the single spin fluid model. The spin contribution to 17 K iso ( T ) and magnetic hyperfine constant 17 A iso were deduced.

43Ca NMR Study of Bismuth-Based High-Tc Superconductors

Abstract As a first step of a study of the electronic properties of CuO2 planes by probing calcium nuclei in the bismuth-based high-Tc materials we report here the structural assignment of Ca NMR lines measured in 43Ca-enriched samples of n = 2 ((Bi,Pb)2Sr2CaCu2O8+x) and n = 3 ((Bi,Pb)2Sr2-Ca2Cu3O10+x) bismuth compounds. Powdered samples were investigated as well as oriented pow ders, achieved by uniaxial alignment of the grains in a 7T magnetic field. For the main calcium site (Ca between two CuO2 planes), we could determine the quadrupolar as well as the shift tensors. The results indicate that, in the same way as yttrium nuclei in YBaCuO, calcium nuclei are sensitive to the magnetic susceptibility of the metallic CuO2 planes.

Spin susceptibility behaviour in the Bi2Sr2Can−1CunO2n+4 compounds : from underdoped to overdoped regime

Abstract We have studied the thermal behaviour of the spin susceptibility, χ spin (T), of the CuO 2 planes in the normal phase. χ spin (T) was measured by 17 O and 43 Ca NMR in various compounds of the Bi 2 Sr 2 Ca n −1 Cu n O 2 n +4 family : a n=3 sample almost optimally doped, an overdoped n=2 sample and a more strongly doped n=1 sample. By contrast to the underdoped case, in the overdoped one, χ spin (T) increases when cooling. Furthermore, this behaviour is enhanced by increasing the doping. χ spin (T) is compared to the macroscopic susceptibility behaviour. On the other hand, our results are consistent with a decrease of the number of charge carriers per copper plane for increasing n.

Charge-ordered state in half-doped Bi-based manganites studied by 17O and 209Bi NMR

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Magnetic properties of (Tl1−xPbx)Sr2CaCu2O7 High-Tc oxide studied by 17O NMR and SQUID: from overdoped superconductor to strongly overdoped metal

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Knight shift in superconducting oxides BaPb1-xBixO3 (x < 0.35)

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Indirect 207Pb−207Pb and 17O−207Pb nuclear spin-spin interactions in the metallic phase of BaPb1−xBixO3

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