3,947 research outputs found
89Y NMR Probe of Zn Induced Local Magnetism in YBa2(Cu(1-y)Zn(y))3O(6+x)
We present detailed data and analysis of the effects of Zn substitution on
the planar Cu site in YBaCuO (YBCO) as evidenced from
our Y NMR measurements on oriented powders. For we find
additional NMR lines which are associated with the Zn substitution. From our
data on the intensities and temperature dependence of the shift, width, and
spin-lattice relaxation rate of these resonances, we conclude that the spinless
Zn 3 state induces local moments on the near-neighbour () Cu
atoms. Additionally, we conjecture that the local moments actually extend to
the farther Cu atoms with the magnetization alternating in sign at subsequent
sites. We show that this analysis is compatible with ESR data taken on
dilute Gd doped (on the Y site) and on neutron scattering data reported
recently on Zn substituted YBCO. For optimally doped compounds
Y resonances are not detected, but a large % -dependent
contribution to the Y NMR linewidth is evidenced and is also attributed
to the occurence of a weak induced local moment near the Zn. These results are
compatible with macroscopic magnetic measurements performed on YBCO
samples prepared specifically in order to minimize the content of impurity
phases. We find significant differences between the present results on the
underdoped YBCO samples and Al NMR data taken on Al
substituted on the Cu site in optimally doped LaCuO. Further
experimental work is needed to clarify the detailed evolution of the impurity
induced magnetism with hole content in the cuprates.Comment: To be published in EPJB 15 pages of text and figures in eps forma
Na atomic order, Co charge disproportionation and magnetism in NaCoO for large Na contents
We have synthesized and characterized four different stable phases of Na
ordered NaCoO, for . Above 100 K they display similar
Curie-Weiss susceptibilities as well as ferromagnetic spin fluctuations
in the CoO planes revealed by Na NMR data. In all phases from
Co NMR data we display evidences that the Co disproportionate already
above 300 K into non magnetic Co and magnetic Co
sites on which holes delocalize. This allows us to understand that metallic
magnetism is favored for these large Na contents. Below 100 K the phases
differentiate, and a magnetic order sets in only for at
22 K. We suggest that the charge order also governs the low energy
scales and transverse couplings
59Co NMR study of the Co states in superconducting and anhydrous cobaltates
Co NMR spectra in oriented powders of NaCoO and in its
hydrated superconducting phase (HSC) NaCoO,1.3HO reveal a
single electronic Co state with identical independent NMR shift tensor.
These phases differ markedly from NaCoO, in which we resolve 3
types of Co sites. The large T variation of their spin susceptibilities and the anisotropy of the orbital susceptibility allow us
to conclude that charge disproportionation occurs, in a non magnetic Co
and two magnetic sites with about 0.3 and 0.7 holes in the multiplet.
The data are consistent with those for the single Co site in the anhydrous and
HSC phase assuming the expected Co charge.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. Let
Anode-Coupled Readout for Light Collection in Liquid Argon TPCs
This paper will discuss a new method of signal read-out from photon detectors
in ultra-large, underground liquid argon time projection chambers. In this
design, the signal from the light collection system is coupled via capacitive
plates to the TPC wire-planes. This signal is then read out using the same
cabling and electronics as the charge information. This greatly benefits light
collection: it eliminates the need for an independent readout, substantially
reducing cost; It reduces the number of cables in the vapor region of the TPC
that can produce impurities; And it cuts down on the number of feed-throughs in
the cryostat wall that can cause heat-leaks and potential points of failure. We
present experimental results that demonstrate the sensitivity of a LArTPC wire
plane to photon detector signals. We also simulate the effect of a 1 s
shaping time and a 2 MHz sampling rate on these signals in the presence of
noise, and find that a single photoelectron timing resolution of 30 ns
can be achieved.Comment: 16 pages, 15 figure
NMR study of the magnetic and metal-insulator transitions in Na0.5CoO2: a nesting scenario
Co and Na NMR are used to probe the local susceptibility and charge state of
the two Co sites of the Na-ordered orthorhombic Na0.5CoO2. Above T_N=86K, both
sites display a similar T-dependence of the spin shift, suggesting that there
is no charge segregation into Co3+ and Co4+ sites. Below T_N, the magnetic long
range commensurate order found is only slightly affected by the metal-insulator
transition (MIT) at T_MIT=51K. Furthermore, the electric field gradient at the
Co site does not change at these transitions, indicating the absence of charge
ordering. All these observations can be explained by successive SDW induced by
two nestings of the Fermi Surface specific to the x=0.5 Na-ordering.Comment: 4 pages, 4 figure
Cu NMR evidence for enhanced antiferromagnetic correlations around Zn impurities in YBa2Cu3O6.7
Doping the high-Tc superconductor YBa2Cu3O6.7 with 1.5 % of non-magnetic Zn
impurities in CuO2 planes is shown to produce a considerable broadening of 63Cu
NMR spectra, as well as an increase of low-energy magnetic fluctuations
detected in 63Cu spin-lattice relaxation measurements. A model-independent
analysis demonstrates that these effects are due to the development of
staggered magnetic moments on many Cu sites around each Zn and that the
Zn-induced moment in the bulk susceptibility might be explained by this
staggered magnetization. Several implications of these enhanced
antiferromagnetic correlations are discussed.Comment: 4 pages including 2 figure
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