[en] A method is described for making a multiphase copper oxide based material Of Y₅Ba₆Cu₁₁ Oxide containing a phase having a zero resistance transition temperature above about 200K, said method comprising: forming a copper oxide based material precursor consisting essentially of Y, Ba, Cu, and 0, which precursor can be oxygenated to yield said multiphase copper oxide based material; and subjecting said precursor to a high temperature heating process at a temperature greater than 900 C for at least 10 hours; subjecting said precursor to a low temperature oxygenation process in an atmosphere comprising at least about 20% oxygen by volume at a temperature less than about 200 C for at least 72 hours to form said multiphase copper oxide based material

[en] In an effort to compare the spin glass characteristics of yttrium--rare earth alloys with those of the noble-metal spin glasses, the susceptibility and heat capacity of Y/sub 0.98/Dy/sub 0.02/ have been measured in the temperature range 2.5--40 K. The low-field ac susceptibility measurement shows the characteristic cusp-like peak at 7.64 K. The magnetic specific heat of the same sample shows a peak at 7.0 K and may be qualitatively described as a semi-cusp. The magnetic entropy change from absolute zero to 7 K is approximately 0.52 of cR ln(2J+1). These results are qualitatively different than previous calorimetric results on the archetypal spin glasses, AuFe and CuMn, where rounded maxima are observed at temperatures above the spin glass transition temperatures

[en] Sodium tellurite glasses containing CuO with the nominal composition [(Na₂O)_0.3(TeO₂)_0.7-x (CuO)_x], where x=0.00, 0.05, 0.15, and 0.20, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS). The binding energies of Te 3p, Te 3d, O 1s, and Cu 2p core levels in these glasses have been measured and compared to the corresponding binding energies in TeO₂ and CuO powders. The Te 3p and Te 3d core levels for the glasses were essentially unchanged from those of TeO₂ powder and have little dependence upon the CuO content. Although the O 1s peak showed a small asymmetry on the higher energy side of the peak in the glasses, it was primarily the result of hydroxide contamination on the glass surface rather than the appearance of non-bridging oxygen atoms arising from a structural change in the TeO₄. For glasses with x=0.05 and 0.15, the Cu 2p peaks were shifted by more than 1 eV towards lower binding energies in comparison to their values in CuO powder, which suggests the presence of Cu⁺ ions in these glasses. The appearance of satellite peaks in the Cu 2p spectra, however, provided definitive evidence for the presence of Cu²⁺ ions in these glass samples as well. The broadened Cu 2p_3/2 peaks were correspondingly decomposed into two distinct peaks separated by approximately 1.25 eV, with the lower energy peak being associated with Cu⁺ and the higher one with Cu²⁺. The relative Cu²⁺ content estimated from the spectral analysis was found to vary from 15% for the x=0.05 glass sample to over 70% for the x=0.20 sample

[en] The paramagnetic Meissner effect (PME), in which the field-cooled-magnetization (FCM) of superconducting samples is positive below the superconducting transition temperature T_c, has been observed in certain ceramic and single-crystal samples of the high-T_c cuprate superconductors and more recently in disk-shaped Nb samples. Through systematic investigations of the conditions for observing the PME in Nb disks, various surface treatments to the Nb disks were found to change both the zero-field-cooled-magnetization (ZFCM) and the FCM, including the appearance of a positive FCM in samples previously not exhibiting the PME as well as the elimination of the PME through surface abrasion. These results suggest that the PME arises from the field distributions created by the flux pinning associated with microstructural defects on the surface layer of the disk

[en] Neutron scattering experiments have been performed on a spin-glass CuMn (5 at. %, T/sub g/ = 27.6 K). Polarized neutron measurements with coarse energy resolution show no change of instantaneous spatial spin correlation below T = 60 K. Unpolarized neutron studies with fine energy resolution (ΔE = 260 μeV) demonstrate that the slowing down of Mn spin fluctuations occur in the same way for all the wave vectors between 0.2 and 4.0 A^-1. These results indicate that the spatial and dynamic spin correlations are completely decoupled in the spin freezing process. We also study the short-range spatial correlation of the ''frozen'' spins at T = 5 K using a simple model, and demonstrate the importance of the ferromagnetic coupling between the third nearest-neighbor Mn moments

[en] In order to provide an independent determination of the hyperfine splitting of the vanadium nucleus in the antiferromagnetic insulating state, the nuclear specific heats of (V/sub 1-x/Cr/sub x/)O₃ and (V/sub 1-x/Al/sub x/)₂O₃ with 0.012 less than or equal to x less than or equal to 0.085 were measured below 1⁰K. The average hyperfine field value of 188.6 kOe is in better agreement with NMR results on V₂O₃ than previous heat-capacity measurements. For x < 0.04, the specific heat, after subtracting the nuclear contribution, is described by a Debye lattice specific heat proprortional T³. However for x > 0.04, this nonnuclear specific heat for the as grown specimens consists not only of a cubic temperature-dependent contribution but also of an anomalous contribution which is linearly dependent on the temperature. After annealing these specimens, the linear temperature-dependent term completely disappears. This anomalous specific heat shows a striking similarity to that of amorphous materials and may likewise result from localized defects whose density is reduced upon annealing the specimens. The observation of longer thermal relaxation times in these annealed specimens gives further support to the similarity with amorphous materials

[en] The magnetic properties of electron-doped manganite La_0.3Ca_0.7MnO₃ and La_0.3Ca_0.7Mn_0.8Cr_0.2O₃ polycrystalline samples prepared by sol-gel technique have been investigated between 5 and 300 K in magnetic fields ranging from 0 to 5 T. The transition at 260 K, attributed to charge ordering in La_0.3Ca_0.7MnO₃, is completely suppressed in the Cr-substituted sample while the onset of a magnetic remanence followed by the appearance of a magnetic irreversibility at lower temperatures is observed in both samples. These features indicate that ferromagnetic clusters coexist with either an antiferromagnetic phase for La_0.3Ca_0.7MnO₃ or a spin-cluster glass phase for La_0.3Ca_0.7Mn_0.8Cr_0.2O₃ at the lowest temperatures. The exponential temperature dependence of the resistivity for the Cr-substituted sample is consistent with the small polaron hopping model for 120 K< T<300 K, while the data are better described by Mott's hopping mechanism for T<120 K. Whereas the parent compound La_0.3Ca_0.7MnO₃ is known to show no magnetoresistance, a large negative magnetoresistance is observed in the La_0.3Ca_0.7Mn_0.8Cr_0.2O₃ sample below 120 K. The appearance of the CMR is attributed to spin dependent hopping between spin clusters and/or between ferromagnetic domains

[en] Existence of granular superconductivity in Y-Ba-Cu-O at 240 K is demonstrated in this study by rf as well as microwave induced dc voltages. These dc voltages exhibit characteristic behaviors that are consistent with those observed for Josephson junctions

[en] The specific heat of niobium in the mixed state has been measured between 0.03 and 0.3 K. The results can be expressed by a sum of electronic and nuclear contributions to the specific heat C = γT + AH²/T², where γ in the mixed state is approximately proportional to the magnetic field H, and A is a constant independent of H and T. An anomaly in the electronic specific heat due to excitations of quasiparticles inside the vortices has not been found down to 0.04 K. Below this temperature the electronic term is overwhelmed by the nuclear contribution so that it is doubtful even if this anomaly exists, that it can be detected by heat-capacity measurements in niobium. The nuclear specific heat is in excellent agreement with values calculated on the basis of nuclear-magnetic-resonance results

[en] This report primarily describes improvements in reproducing and characterizing YBaCuO materials exhibiting zero-resistance at temperatures above 200 K. The most notable improvements were found in several single crystal samples of nominal YBa₂Cu₃O₇ which exhibited an anisotropic resistivity with the resistance dropping to zero at about 260 K when measured in the a-b plane of the crystal. Magnetic measurements on similar crystals as well as on melt-textured YBa₂Cu₃O₇ platelets showed hysteretic behavior below 240 K similar to the flux trapping observed in type-2 superconductors. From the systematic electrical measurements involving various lead configurations, the observation of magnetic hysteresis with no bulk diamagnetic Meissner response, and preliminary HRTEM and SEM studies, the (zero-resistance) transition around 260 K appears to be superconducting in nature and associated with a defect structure or stacking fault layers (< 1μm) that exists in these materials. Although the current capacity in these crystals is presently limited by contact heating to ∼30μA (current density of ∼1 A/cm²), there is an indication of a 1-mA zero-voltage current after keeping the sample in an oxygen environment for two months