N. Blanchard

Normal State Magnetic Properties of Ni and Zn Substituted in YBa2Cu3O6+x: Hole-Doping Dependence

We present SQUID susceptibility data on Zn and Ni substituted YBa2Cu3O6 + x. Cross-checks with NMR yield an unprecedented accuracy in the estimate of the magnetic susceptibility associated with the substituents, from the underdoped to the lightly overdoped case. This allows us to determine the Weiss temperature θ for YBCO: its value is very small for all hole dopings nh. Since in conventional metals the Kondo temperature TK > θ; in contrast, increasing nh produces a reduction of the small moment induced by Zn2+ and a nearly constant effective moment for Ni2+ corresponding to a spin 1/2 rather than to a spin 1.

Absence of static phase separation in the high T(c) cuprate YBa(2)Cu(3)O(6+y).

We use 89Y NMR in YBa(2)Cu(3)O(6+y) in order to evaluate with high sensitivity the distribution of hole content p in the CuO2 planes. For y=1 and y=0.6, this hole doping distribution is found narrow with a full width at half maximum smaller than Deltap=0.025. This rules out any large static phase separation between underdoped and optimally doped regions in contrast with the one observed by STM in Bi2212 and by NQR in LaSrCuO. This establishes that static electronic phase separation is not a generic feature of the cuprates.

Evidence of a single nonmagnetic Co 3 + state in the Na 1 CoO 2 cobaltate

Macroscopic magnetization, muon spin rotation (muSR), and NMR measurements were carried out to study magnetism in the Na1CoO2 cobaltate. Using SQUID measurements, Na1CoO2 is shown to have a bulk magnetic susceptibility much lower and flatter than that of NaxCoO2 with x=0.7-0.9. In fact, muSR yields a signal of mostly nonmagnetic origin, which is attributed to the x=1 phase. The intrinsic cobalt spin susceptibility corresponding to this x=1 phase is measured using Na NMR. It is indeed found to be almost zero, in agreement with a low-spin 3+ charge state of all cobalt atoms. This single state of Co ions in CoO2 planes is confirmed by Co NMR, whose determination of cobalt shift and quadrupolar parameters allows us to give a reference value of the Co3+ orbital shift in cobaltates.

Oxygen nonstoichiometry, point defects and critical temperature in superconducting oxide Bi2Sr2CaCu2O8+Δ

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Spin correlations and cobalt charge states: Phase diagram of sodium cobaltates

Co NMR spectra in oriented powders of Na

Na atomic order, Co charge disproportionation and magnetism in NaxCoO2 for large Na contents

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Macroscopic magnetic properties of Ni and Zn substituted YBa2Cu3Oχ

CoO

Comparison of Ni and Zn doped YBa2Cu3O7 by 89Y NMR

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Oxygen excess in Bi-2212: study of a Pb-substituted compound

and in its hydrated superconducting phase (HSC) Na