Gd3+ ESR determination of the local spin susceptibility in Gd:YBa2Cu3Oy high-temperature superconductors

Enhanced emission of encaged-OH--free Ca12(1-x)Sr12xAl14O33:0.1%Gd3+ conductive phosphors via tuning the encaged-electron concentration for low-voltage FEDs

Encaged-OH^--free Ca_12(1-x)Sr_12xAl₁₄O₃₃:0.1%Gd³⁺ conductive phosphors were prepared through a melt-solidification process in combination with a subsequent heat treatment. Absorption spectra showed that the maximum encaged-electron concentration was increased to 1.08 × 10²¹ cm^-3 through optimizing the doping amount of Sr²⁺ (x = 0.005). Meanwhile, FTIR and Raman spectra indicated that pure Ca_11.94Sr_0.06Al₁₄O₃₃:0.1%Gd³⁺ conductive phosphor without encaged OH^- and C₂^2- anions was acquired. For the conductive powders heat-treated in air for different times, the encaged-electron concentrations were tuned from 1.02 × 10²¹ to 8.3 × 10²⁰ cm^-3. ESR, photoluminescence, and luminescence kinetics analyses indicated that the emission at 312 nm mainly originated from Gd³⁺ ions surrounded by encaged O^2- anions, while Gd³⁺ ions surrounded by encaged electrons had a negative contribution to the UV emission due to the existence of an energy transfer process. Under low-voltage electron-beam excitation (3 kV), enhanced cathodoluminescence (CL) of the conductive phosphors could be achieved by tuning the encaged-electron concentrations. In particular, for the encaged-OH^--free conductive phosphor, the emission intensity of the CL was about one order of magnitude higher than that of the conductive phosphor containing encaged OH^- anions. Our results suggested that the encaged-OH^--free conductive phosphors have potential application in low-voltage FEDs.

Enhancement of encaged electron concentration by Sr2+ doping and improvement of Gd3+ emission through controlling encaged anions in conductive C12A7 phosphors

Conductive C12A7:0.1%Gd³⁺,y%Sr²⁺ phosphors have been prepared through hydrogen route in combination with subsequent UV-irradiation.

Magnetic-field-induced low-energy spin excitations in YBa(2)Cu(4)O(8) measured by high field Gd(3+) electron spin resonance

We have measured the spin susceptibility, chi(s), of the CuO(2) planes in the underdoped high T(c) superconductor, YBa(2)Cu(4)O(8) by Gd(3+) electron spin resonance (ESR) in single crystals and aligned powders in fields up to 15.4 T. At low temperatures and high fields, chi(s) is enhanced slightly in the B parallel c orientation with respect to the B perpendicular c orientation. The enhancement at 15.4 T (approximately equal to 0.15H(c2)) at 16 K (0.2 T(c)) is small: approximately 10% of chi(s)(T(c)), suggesting that the second critical field of superconductivity, H(c2) approximately equal to 100 T, would not suppress the pseudogap. This work demonstrates the potential of high field ESR in single crystals for studying high T(c) superconductors.

Dynamics of the local moment induced by nonmagnetic defects in cuprates

We present a study of the spin dynamics of magnetic defects induced by Li substitution of the plane Cu in the normal state of YBa2Cu3O6+x. The fluctuations of the coupled Cu magnetic moments in the vicinity of Li are probed by near-neighbor 89Y and 7Li NMR spin lattice relaxation. The data indicate that the magnetic perturbation fluctuates as a single entity with a correlation time tau which scales with the local static susceptibility. This behavior is reminiscent of the low T Kondo state of magnetic impurities in conventional metals. Surprisingly it extends well above the "Kondo" temperature for the underdoped pseudogapped case.