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This work reports a systematic study of polycrystalline samples of ${\mathrm{Sm}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ (0.15\ensuremath{\le}x\ensuremath{\le}0.18) obtained from a sol-gel precursor and subjected to different cooling rates after reduction. A double resistive superconducting transition is a common feature of all samples studied, suggesting that this is an intrinsic property of these polycrystalline compounds. At an upper temperature ${\mathit{T}}_{\mathit{c}\mathit{i}}$, there is a fairly sharp drop in the magnitude of the electrical resistivity, which is followed by a well-defined plateau down to a lower temperature ${\mathit{T}}_{\mathit{c}\mathit{j}}$. At this temperature, Josephson coupling between superconducting islands is believed to complete the transition to the zero resistance state. From the compositional dependence of electrical resistivity, we infer that ${\mathit{T}}_{\mathit{c}\mathit{i}}$ decreases slightly from x=0.15 through x=0.18, while ${\mathit{T}}_{\mathit{c}\mathit{j}}$ shows a maximum for x=0.16. With increasing excitation current, no significant changes in the behavior of the electrical resistivity between ${\mathit{T}}_{\mathit{c}\mathit{i}}$ and ${\mathit{T}}_{\mathit{c}\mathit{j}}$ are observed, while a dramatic broadening and a shift of the transition at ${\mathit{T}}_{\mathit{c}\mathit{j}}$ towards lower temperatures are found. Magnetic-susceptibility measurements reveal appreciable diamagnetism just below the coupling temperature ${\mathit{T}}_{\mathit{c}\mathit{j}}$ suggesting that superconducting properties are really confined to small regions, with size comparable to the London penetration depth.The average size of these regions are estimated to be between \ensuremath{\sim}6 and 300 \AA{}, in good agreement with recent estimates obtained from magnetoresistance measurements on polycrystalline ${\mathrm{Sm}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ (0.14\ensuremath{\le}x\ensuremath{\le}0.17) samples and with both neutron-diffraction studies and M\"ossbauer spectroscopy measurements in the isomorphic compound ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ (0.0\ensuremath{\le}x\ensuremath{\le}0.18). All the observed macroscopic properties, as well as the absence of a peak in the specific heat at ${\mathit{T}}_{\mathit{c}\mathit{i}}$, are discussed within the framework of a granular superconductor model. In addition, we give qualitative arguments suggesting the importance of charging effects in the macroscopic properties of these polycrystalline samples.

Investigations of Y1−x M x Ba2Cu3O7−δ (M=Ce, Th)c-axis oriented thin film specimens show that the rate of depression ofT c withx is larger for M=Th, than for M=Ce and Pr, and suggest that Ce, like Th, is tetravalent in this compound. Hall effect measurements on Y1−x Pr x Ba2Cu3O7−δ single crystals reveal aT 2 dependence of the cotangent of the Hall angle in the normal state and a “negative Hall anomaly” belowT c in the superconducting state, in agreement with recent reports. Our research shows that the depth, Δ, of the negative Hall signal scales withT/T c and that the maximum value of Δ decreases linearly withx and vanishes atx≈0.24. Magnetoresistance measurements on Y1−x Pr x Ba2Cu3O7−δ single crystals indicate that the irreversibility lineH(T *) obeys a universal scaling relation characterized by anm=3/2 power law nearT c, with a crossover to a more rapid temperature dependence of belowT/T c ≈0.6, similar to that observed for polycrystalline specimens.

Synthesis of La/sub 1-x/Sr/sub x/MnO/sub 3/ (x=0.1, 0.2 and 0.3) by homogenous coprecipitation method using urea as precipitant agent is reported. The particles are smaller than 200 nm after heating at 950/spl deg/C. Temperature dependence of the electrical resistivity was found to be similar to the reported value for single crystals of these manganites.

Measurements are presented of the complex dynamic Young's modulus of NdNiO${}_{3}$ and Nd${}_{0.65}$Eu${}_{0.35}$NiO${}_{3}$ through the metal-insulator transition (MIT). Upon cooling, the modulus presents a narrow dip at the MIT followed by an abrupt stiffening of $\ensuremath{\sim}$$6%$. The anomaly is reproducible between cooling and heating in Nd${}_{0.65}$Eu${}_{0.35}$NiO${}_{3}$ but appears only as a slow stiffening during cooling in undoped NdNiO${}_{3}$, in conformance with the fact that the MIT in $R$NiO${}_{3}$ changes from strongly first order to second order when the mean $R$ size is decreased. The elastic anomaly seems not to be associated with the antiferromagnetic transition, which is distinct from the MIT in Nd${}_{0.65}$Eu${}_{0.35}$NiO${}_{3}$ . It is concluded that the steplike stiffening is due to the disappearance or freezing of dynamic Jahn-Teller (JT) distortions through the MIT, where the JT active Ni${}^{3+}$ is disproportionated into alternating Ni${}^{3+\ensuremath{\delta}}$ and Ni${}^{3\ensuremath{-}\ensuremath{\delta}}$. The fluctuating octahedral JT distortion necessary to justify the observed jump in the elastic modulus is estimated as $\ensuremath{\sim}$$3%$ but does not have a role in determining the MIT, since the otherwise-expected precursor softening is not observed.

The energy barrier distribution Eb of five samples with different concentrations x of Ni nanoparticles using scaling plots from ac magnetic susceptibility data has been determined. The scaling of the imaginary part of the susceptibility Chi"(nu, T) vs. Tln(t/tau_0) remains valid for all samples, which display Ni nanoparticles with similar shape and size. The mean value increases appreciably with increasing x, or more appropriately with increasing dipolar interactions between Ni nanoparticles. We argue that such an increase in constitutes a powerful tool for quality control in magnetic recording media technology where the dipolar interaction plays an important role., Comment: 3 pages, 3 figures, 1 table

Oxides RNiO3 (R = rare-earth, R # La) exhibit a metal-insulator (MI) transition at a temperature TMI and an antiferromagnetic (AF) transition at TN. Specific heat (CP) and anelastic spectroscopy measurements were performed in samples of Nd1-xEuxNiO3, 0 = 0.25, differences between cooling and warming curves are negligible, and two well defined peaks are clearly observed: one at lower temperatures, that define TN, and the other one at TMI. An external magnetic field of 9 T had no significant effect on these results. The elastic compliance (s) and the reciprocal of the mechanical quality factor (Q^-1) of NdNiO3, measured upon warming, showed a very sharp peak at essentially the same temperature obtained from CP, and no peak is observed upon cooling. The elastic modulus hardens below TMI much more sharply upon warming, while the cooling and warming curves are reproducible above TMI. On the other hand, for the sample with x = 0.35, s and Q^-1 curves are very similar upon warming and cooling. The results presented here give credence to the proposition that the MI phase transition changes from first to second order with increasing Eu doping., 3 pages and 3 figures. To be presented at MMM 2010

Angle-resolved photoemission measurements for bulk single crystals of ${\mathrm{Nd}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ with x=0.15 show that the spectral weight which builds in the gap of the x=0 insulator displays a Luttinger Fermi surface, the first such observation for a material which is electron doped and which must be driven metallic by alloying. This finding greatly strengthens our previous ocnclusion that the metal's chemical potential lies in gap-filling spectral weight, and sharpens the distinction between theories in which this does or does not occur.

We report a systematic study of the double resistive superconducting transition in carefully prepared polycrystalline samples of the electron-doped superconducting series ${\mathrm{Sm}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathit{y}}$ for 0.12\ensuremath{\le}x\ensuremath{\le}0.20. From high-resolution x-ray-diffraction measurements, the solubility limit of Ce in this series is slightly greater than 0.16. An intrinsic double resistive transition present in all superconducting compounds is attributed to the granularity of these polycrystalline samples. There is a partial transition when the grains become superconducting at a temperature ${\mathit{T}}_{\mathit{c}1}$, and coupling between grains at a lower temperature ${\mathit{T}}_{\mathit{c}2}$ apparently completes the transition. Only the transition associated with coupling between grains is observed in magnetic-susceptibility measurements due to inhomogeneous grains and large penetration depths. From compositional dependences of resistive and magnetic measurements, the superconducting volume fraction increases linearly with increasing dopant concentration up to the solubility limit, while the best coupling between grains is at a dopant concentration of 0.15. Thus, there is a subtle relationship between doping and coupling in this series. Also, arguments for a true thermodynamic phase transition at ${\mathit{T}}_{\mathit{c}2}$ are given.

We have measured electrical resistance R(T), magnetization M(T), and for the first time impedance spectroscopy Z(T,ω) of polycrystalline samples of La0.3Pr0.4Ca0.3MnO3 compounds. The combined results suggest the coexistence of two metallic ferromagnetic phases below the Curie temperature of the system. The R(T) data exhibit two important features: the occurrence of a metal–insulator (MI) transition at temperatures close to TMI≈170 K and a large thermal hysteresis below TMI. The first feature was found to be associated with the development of ferromagnetism and takes place when the magnetization of the samples becomes about 15% of its saturated value at low temperatures. The second feature suggests two contributions to R(T) below the Curie temperature TC. The Z(T,ω) data taken from 77 to 300 K and frequency varying from 5 to 107 Hz are much more valuable. These results reveal two well defined bulk contributions to the transport properties of these manganites below ∼170 K: one occurring at high frequencies ...

The intermetallic UCu4+xAl8−xcompounds (0.1⩽x⩽1.95) have remarkable electronic and magnetic properties. The Cu-poor compositions within this x-range are antiferromagnetic (AF). The Neel temperature (TN) drops gradually from ≈36 K for x=0.1 until AF is completely suppressed near x=1.1, while the Sommerfeld coefficient (γ) increases dramatically with x, reaching a maximum value of 750 mJ/mol K2 for x=1.75. Reported in this investigation are magnetoresistance (MR) and magnetic susceptibility (χ) measurements at low temperatures (T) and high magnetic fields (B). The isothermal MR data below 40 K crosses over from positive in the low-x to negative in the high-x range. These results are interpreted in the context of spin fluctuations, hybridization, and non-magnetic atomic disorder.

We have used RF sputtering to produce thin films of NdNiO3 on glass substrates at different temperatures and atmospheres of deposition. The as-grown films were amorphous and a heat treatment at 650°C under oxygen pressure of 60 bar results in their crystallization. Transport measurements on these films revealed the occurrence of a metal–insulator MI transition at different temperatures 150

Magnetic nanoparticles (NP) of magnetite (Fe3O4) coated with oleic acid (OA) and dodecanoic acid (DA) were synthesized and investigated through Transmission Electron Microscopy (TEM),magnetization M, and ac magnetic susceptibility measurements. The OA coated samples were produced with different magnetic concentrations (78, 76, and 65%) and the DA sample with 63% of Fe3O4. Images from TEM indicate that the NP have a nearly spherical geometry and mean diameter ~ 5.5 nm. Magnetization measurements, performed in zero field cooled (ZFC) and field cooled (FC) processes under different external magnetic fields H, exhibited a maximum at a given temperature TB in the ZFC curves, which depends on the NP coating (OA or DA), magnetite concentration, and H. The temperature TB decreases monotonically with increasing H and, for a given H, the increase in the magnetite concentration results in an increase of TB. The observed behavior is related to the dipolar interaction (DI) between NP which seems to be an important mechanism in all samples studied. This is supported by the results of the ac magnetic susceptibility Xac measurements, where the temperature in which X' peaks for different frequencies follows the Vogel-Fulcher model, a feature commonly found in systems with dipolar interactions. Curves of H vs. TB/TB(H=0) for samples with different coatings and magnetite concentrations collapse into a universal curve, indicating that the qualitative magnetic behavior of the samples may be described by the NP themselves, instead of the coating or the strength of the dipolar interaction. Below TB, M vs. H curves show a coercive field (HC) that increases monotonically with decreasing temperature. The saturation magnetization (MS) follows the Bloch's law and values of MS at room temperature as high as 78 emu/g were estimated, a result corresponding to ~80% of the bulk value. The overlap of M/MS vs. H/T curves for a given sample and the low HC at high temperatures suggest superparamagnetic behavior in all samples studied. The overlap of M/MS vs. H curves at constant temperature for different samples indicates that the NP magnetization behavior is preserved, independently of the coating and magnetite concentration., 8 pages and 9 figures

This is a phase III, prospective, randomized, double-blind, placebo-controlled clinical trial on lodenafil carbonate (LC), a novel phosphodiesterase 5 inhibitor developed in Brazil.Expanding information on LC efficacy and safety.International Index of Erectile Function (IIEF) erectile domain, positive answers to the sexual encounter profile (SEP)-2 and SEP-3 questions and incidence of adverse events (AEs).A total of 350 men with erectile dysfunction (ED) of all degrees were randomized to placebo, LC 40 mg or LC 80 mg and followed for 4 weeks. They completed the IIEF and answered the SEP questions 2 and 3 after each intercourse without and with the use of LC.IIEF Erectile Domain scores without and with the use of medication were the following (mean [M] +/- standard deviation [SD]): placebo = 13.9 +/- 5.2 and 14.8 +/- 7.8; LC 40 mg = 13.6 +/- 5.3 and 18.6 +/- 8.0; LC 80 mg = 13.4 +/- 4.9 and 20.6 +/- 7.7 (analysis of variance [ANOVA] P0.01). Positive answers to SEP-2 without and with the use of medication were the following (M +/- SD): placebo = 55.3 +/- 43.2% and 52.1 +/- 41.4%; LC 40 mg = 46.4 +/- 44.3% and 63.5 +/- 42.0%; LC 80 mg = 50.2 +/- 40.9% and 80.8 +/- 32.3% (ANOVA P0.01). Positive answers to SEP-3 were the following: placebo = 20.2 +/- 32.3% and 29.7 +/- 38.1%; LC 40 mg = 19.6 +/- 34.3% and 50.8 +/- 44.4%; LC 80 mg = 20.8 +/- 33.2% and 66.0 +/- 39.3% (ANOVA P0.01). The patients with at least one AE were placebo = 28.7%, LC 40 mg = 40.9%, and LC 80 mg = 49.5%. AEs whose incidence was significantly higher with LC than with placebo included rhinitis, headache, flushing, visual disorder, and dizziness.LC showed a satisfactory efficacy-safety profile for oral therapy of ED.

Magnetic-susceptibility measurements as a function of temperature and magnetic field were performed in polycrystalline samples of ${\mathrm{Gd}}_{2}$${\mathrm{CuO}}_{4}$, ${\mathrm{Gd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4}$, and ${\mathrm{Gd}}_{1.8}$${\mathrm{Nd}}_{0.2}$${\mathrm{CuO}}_{4}$. The previously observed anomaly in the magnetic susceptibility of ${\mathrm{Gd}}_{2}$${\mathrm{CuO}}_{4}$ at 20 K associated with the possible existence of weak ferromagnetic behavior was found to be strongly suppressed by ${\mathrm{Ce}}^{4+}$ and ${\mathrm{Nd}}^{3+}$ doping. Below 6.8 K the susceptibility of ${\mathrm{Gd}}_{2}$${\mathrm{CuO}}_{4}$ is almost field independent above a few kilo-oersted, up to at least 40 kOe, suggesting the occurrence of a spin-flop phase. An exchange field of 35 kOe and an anisotropy field of 20 Oe were obtained.

Polycrystalline samples of LnNi0.3Co0.7O3 (Ln=La, Pr) were prepared through sol-gel precursors. The samples were subjected to several heat treatments at temperatures ranging from 650 to 1000 °C and under oxygen pressure as high as 70 bar. Characterizations of x-ray powder diffraction XRD magnetization M(T), and ac magnetic susceptibility χac(T) were performed on these compounds. The results of XRD showed that samples of LaNi0.3Co0.7O3 crystallize in a rhombohedral distorted perovskite structure (R3c) and that PrNi0.3Co0.7O3 compounds displayed an orthorhombically distorted structure (Pbnm). The temperature dependence of M(T) revealed the presence of a sharp cusp occurring at temperatures TP∼60 and ∼ 30 K for Ln=La and Pr, respectively. Below TP, the M(T) curves taken after different thermal cycles, i.e., field cooled and zero-field cooled processes, are histories dependent on the magnitude of M(T) decreasing with increasing applied magnetic field. We have also observed that TP decreases with increasing a...

The role of dipolar interactions among Ni nanoparticles (NP) embedded in an amorphous SiO2/C matrix with different concentrations has been studied performing ac magnetic susceptibility Chi_ac measurements. For very diluted samples, with Ni concentrations < 4 wt % Ni or very weak dipolar interactions, the data are well described by the Neel-Arrhenius law. Increasing Ni concentration to values up to 12.8 wt % Ni results in changes in the Neel-Arrhenius behavior, the dipolar interactions become important, and need to be considered to describe the magnetic response of the NPs system. We have found no evidence of a spin-glasslike behavior in our Ni NP systems even when dipolar interactions are clearly present., 7 pages, 5 figures, 3 tables

High-resolution synchrotron x-ray powder diffraction in ${\text{La}}_{0.7}{\text{Ca}}_{0.3}{\text{MnO}}_{3}$ shows in detail a first-order structural phase transition from orthorhombic (space-group $Pnma$) to rhombohedral (space-group $R\overline{3}c$) crystal structures near ${T}_{S}=710\text{ }\text{K}$. Magnetic susceptibility measurements show that the rhombohedral phase strictly obeys the Curie-Weiss law as opposed to the orthorhombic phase. A concomitant change in the electrical resistivity behavior, consistent with an alteration from nonadiabatic to adiabatic small polaron hopping regimes, was also observed at ${T}_{S}$. The simultaneous change in transport and magnetic properties are identified as a transition from a correlated polaron liquid for $Tl{T}_{S}$ to an uncorrelated polaron gas for $Tg{T}_{S}$, driven by the change in the crystal symmetry.

The colossal magnetoresistance CMR effect in perovskite manganese oxides results from the strong interplay between lattice, charge, and spin degrees of freedom.1 In the canonical compound La0.70A0.30MnO3, smaller A ions reduce the average Mn-O-Mn bond angle, which weakens the ferromagnetic double-exchange DE interaction.2 A similar effect occurs when small rare-earth ions such as Y are substituted for La.3 YMnO3 is a superexchange SE antiferromagnet TN=70 K with hexagonal crystal structure, ferroelectric behavior below 900 K , and frustrated magnetism.4 Y ionic radius5 of 1.019 A substitution for La ionic radius of 1.160 A in La0.70A0.30MnO3 will lead to significant local distortions and competition between DE and SE interactions, which might also promote disorder and frustration within the magnetic lattice. In some cases a spin-glass-like state may result or the level of frustration could be high enough to prevent the establishment of long-range magnetic order.6 Indeed, several studies indicate that the ferromagnetic FM transition in manganese oxides can be suppressed through doping of Y, Ga, Gd, or Dy leading to a cluster-glass state.7–9 Although the magnetic and transport properties of Y-substituted La0.70Ca0.30MnO3 have been well studied, heat capacity at constant pressure CP and thermal expansion have received less attention. Herein we show that substitution of 15% Y for La suppresses the anomaly in CP at the ferromagnetic transition temperature TC. In contrast with the CP data, high-resolution thermal-expansion measurements reveal a distinct anomaly in the volume at TC. Careful comparison of CP of the undoped and doped samples reveals a very broad feature in La0.55Y0.15Ca0.30MnO3. Furthermore, thermodynamic analysis indicates that the peak in CP at TC should be small and broad; this analysis correctly predicts an extremely large pressure effect on TC as well. The results are discussed in terms of local strain fields induced by the smaller Y ions, and the resulting competition between DE and SE interactions, which leads to an inhomogeneous ferromagnetic state composed of FM and canted-FM regions. Polycrystalline samples of La0.70−xYxCa0.30MnO3 x=0.0 and 0.15 were prepared through a sol-gel method, which provides better chemical homogeneity, smaller particle size, and higher density 90% of theoretical density than a standard solid-state reaction. The dried gel was heat treated at 1000 °C and 1100 °C in air for 30 h, subsequently pressed into pellets, and subjected to a final heat treatment at 1200 °C in air for 30 h. Rietveld refinement space group Pnma of x-ray powder-diffraction data confirmed the single-phase nature. Heat capacity was measured using a Quantum Design PPMS. A fused quartz capacitive dilatometer was used to measure the linear thermal expansion with a sensitivity in l of 0.1 A. ac and dc magnetization M T ,H , P under zero-field cooling ZFC and field cooling FC , was measured in a SQUID magnetometer. For hydrostatic pressure measurements, a Cu-Be clamp-type cell was placed in the magnetometer with n-pentane-isoamyl alcohol 50:50 mixture as a pressure medium. Pressure was determined with a superconducting tin manometer placed in the cell with the sample. The dc magnetization ZFC and FC versus temperature of the samples with x=0.0 and 0.15 is shown in Fig. 1. The saturated magnetic moments, determined from the curves at 5 T and 5 K, were found to be 3.6 and 3.3 B for x=0 and 0.15, respectively. These are slightly smaller than expected 3.7 B for a 70:30 ratio of Mn3+/Mn4+ ions but indicate that both samples display ferromagnetic order. The sample with x=0.15 has a smaller magnetic moment, which suggests a canted FM alignment. For x=0, TC=250 K at H=0.1 T. Yttrium doping causes a strong decrease of TC to 90 K and 100 K upon cooling and warming, respectively; the hysteresis disappears at 5 T. This large thermal hysteresis was not observed for x=0. La0.55Y0.15Ca0.30MnO3 is known to exhibit

The effects of dc excitation current on the current-voltage curves of polycrystalline samples of ${\mathrm{Nd}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{Mn}}_{0.96}{\mathrm{Cr}}_{0.04}{\mathrm{O}}_{3}$ were investigated. The experimental results show that an abrupt jump of the voltage is concomitant with a huge increase in the temperature of the sample. A simple model and estimates for Joule self-heating effects support the experimental data. Moreover, the data strongly suggest that both the current localization in the metallic paths and local Joule self-heating effects are essential ingredients to understand the current-induced phase transition in phase-separated manganites.

We carried out an investigation of the effect of quasi‐hydrostatic pressures up to 1.2 GPa in pure and Rh‐doped RuSr2GdCu2O8 compounds, by means of measurements of electrical resistivity in magnetic fields up to 9 T. The onset temperatures for superconductivity, and for magnetic order in the undoped RuSr2GdCu2O8 compound are Tc ≈ 50 K, and Tm ≈ 133 K, respectively. The partial substitution of Rh for Ru lowers both these transitions temperatures. However, the effect of pressure for all compositions studied, up to 10% substitution, was to increase both Tc, and Tm. The effect of pressure on the upper critical magnetic field of the pure, and Rh‐doped compounds is discussed.

We have studied the structural, magnetic, and transport properties of polycrystalline (Nd1−xGdx)1.85Ce0.15CuO4−y; x=0.0, 0.05, 0.10, 0.25, and 0.50; produced under different atmospheres and cooling rates after the reduction process. From x-ray analysis the T′-structure is preserved for all samples studied. We also found that quenched samples in argon atmosphere exhibit superconductivity below ∼22 K. The temperature dependence of the electrical resistivity ρ(T) displays a striking double resistive superconducting transition with no evidence of a zero resistance state down to 1.5 K. The electrical resistivity has a ≈20% drop at the upper critical temperature Tci followed by a plateau down to a lower temperature Tcj. While Tci is both weakly dependent on the Gd content and external applied magnetic field, the behavior of ρ(T) at low temperatures is strongly sensitive to the Gd concentration, excitation current, and applied magnetic fields. Also, the behavior of ρ(T) below ≈3 K is almost field independent. Th...

A new method for analyzing second-order phase transitions is presented and applied to the polaronic system La(0.7)Ca(0.3)MnO3. It utilizes heat capacity and thermal expansion data simultaneously to correctly predict the critical temperature's pressure dependence. Analysis of the critical phenomena reveals second-order behavior and an unusually large heat capacity exponent.

We have performed a systematic study of the structural, transport, and magnetic properties of polycrystalline samples of the magnetic superconductors Ru1-xIr xSr2GdCu2O8; x = 0, 0.02, 0.05, 0.10, and 0.15. The samples were prepared by solid state reaction and sintered at 1060 ºC for 72 h under O2 flow. X-ray diffraction analysis shows that all samples are nearly single phase and that the lattice parameters are independent of Ir content. Transport properties measurements revealed that the Ru substitution by Ir results in a decrease of Tc,onset from ~50 K (x = 0) to ~30 K (x = 0.10). Further addition of Ir (x > 0.10) causes an evolution from metallic to nonmetallic behavior of r(T). We have also found that magnetic order develops in the undoped Ru-1212 materials near T M ~ 130 K. This temperature decreases linearly with increasing Ir content at the rate of ~ -1.6 K / Ir at.%, suggesting that Ir effectively substitutes Ru in the RuO planes. A subtle drop in r(T) is observed close to T M, probably due to the suppression of the spin-flip scattering. The magnetoresistivity measurements revealed that the temperature Tc,zero, in which r(T) ~ 0, decreases rapidly for low applied magnetic fields (H < 2 T), and that this drop becomes much less pronounced in higher magnetic fields (2 < H < 18 T). The appreciable broadening of r(T) curves at low magnetic fields is reminiscent of the behavior in high-Tc materials showing granular behavior, as for example in Sm1.85Ce0.15CuO4-y.

Summary form only given. Lanthanum strontium doped manganites have attracted renewed attention at present due to the observation of interesting electrical and magnetic properties such as a colossal negative magnetoresistance, catalytic activity, field-sensing, among others. Several preparation methods are described in the literature concerning the so-called wet-chemical routes. This work describes a nanoparticle La/sub 1-x/Sr/sub x/MnO/sub 3/ (x = 0.1, 0.2 and 0.3) synthesis by the homogenous coprecipitation method using urea as precipitant agent. The samples were characterized by X-ray powder diffraction, transmission electron microscopy (TEM) and electrical resistivity as a function of temperature.

Polycrystalline samples of Eu2−xCexCuO4−y (0.0≤x≤0.18) were prepared from a sol‐gel precursor and sintered in air at different temperatures. From the x‐ray diffraction results, the beginning of Eu2−xCexCuO4−y phase formation is observed by increasing the sintering temperature up to 500 °C, as indicated by the presence of very broad Bragg reflections belonging to the desired phase. At 700 °C, Eu2−xCexCuO4−y coexists with Eu2O3, CeO2, and CuO. Additional sintering at 950 °C in air for 20 h results in single phase materials. The effectiveness of Eu replacement by Ce in the Eu2CuO4 pristine phase has been confirmed by a decrease in the lattice parameter c with increasing x. Also, the solubility limit of Ce in these series was found to be higher than x=0.15. The results of thermal analysis reveal that the eutectic temperature Te≊1020 °C is Ce independent. On the other hand, the peritectic temperature Tp increases significantly with increasing Ce concentration. It is close to Tp≊1180 °C for Eu2CuO4 and Tp≊1195 ...

A systematic study of transport and magnetic properties of polycrystalline Sm2−xCexCuO4−y (0.15≤x≪0.18) specimens obtained from a sol‐gel precursor reveals a striking double resistive superconducting transition. One of the resistive transitions takes place at a temperature Tci and is almost insensitive to Ce concentration, applied magnetic field, and current density, while the other transition occurs at a lower temperature Tcj and is very sensitive to Ce content, applied magnetic field, and current density. Alternating‐current magnetic susceptibility χac measurements reveal two interesting features. There is only one contribution to the diamagnetic signal below ∼20 K, which is particularly evident in the resistive component χ‘ of χac where a peak at Tcj can be identified. The application of an applied magnetic field shifts the χ‘ peak to lower temperatures and reveals a spin‐glass‐like behavior. All the results can be satisfactorily explained in terms of weakly linked Josephson junctions between small sup...

Pre-reacted powders of (Bi-Pb)2Sr2Ca2Cu3O10+δ (Bi-2223) were consolidated by using the spark plasma sintering (SPS) technique under vacuum and at two different temperatures TD: 750 and 830 °C. The results indicate the occurrence of grains with core-shell morphology, where the shell is oxygen deficient. A post-annealing heat treatment (PAHT), performed in air, at 750 °C, and for a brief time interval, is responsible for a 10 to 25-fold increase in the transport superconducting current density at 77 K. The role of the oxygen-deficient shell, before and after the PAHT, was investigated by means of magnetic and transport measurements. We argue that the PAHT is two folds: (i) it is responsible for the decrease of the width of the oxygen-deficient shell, then increasing the oxygen content along the grain boundaries; (ii) it promotes the formation of conduction current paths along the grain boundaries of the SPS material.

We performed measurements of magnetic susceptibility, electrical resistivity, and magnetoresistance in magnetic fields of up to 18 T in the magnetic superconductor ${\mathrm{RuGd}}_{1.4}{\mathrm{Ce}}_{0.6}{\mathrm{Sr}}_{2}{\mathrm{Cu}}_{2}{\mathrm{O}}_{10\ensuremath{-}\ensuremath{\delta}}$ synthesized in oxygen pressures up to 95 atm. The magnetic-susceptibility data show the occurrence of an antiferromagnetic state below ${T}_{N}\ensuremath{\sim}175\mathrm{K},$ followed by the development of a weak ferromagnetic state near ${T}_{M}\ensuremath{\sim}100\mathrm{K},$ and followed further by the onset of superconductivity (SC) at ${T}_{c}\ensuremath{\sim}42\mathrm{K}.$ The electrical resistivity as a function of temperature shows an evolution from nonmetal-to-SC behavior in samples prepared in a flux of ${\mathrm{O}}_{2}$ to a well defined metal-like behavior in samples prepared under 95 atm pressure of ${\mathrm{O}}_{2}.$ The electron-phonon coupling constant was calculated from transport data to be ${\ensuremath{\lambda}}_{\mathrm{tr}}\ensuremath{\sim}0.17,$ a value comparable with other cuprates, indicating weak electron-phonon coupling in these ruthenates. The values of the upper critical field ${H}_{c2}$ for the ${\mathrm{O}}_{2}$ high-pressure treated samples were obtained from the magnetoresistivity data yielding ${H}_{c2}^{\mathrm{ab}}(0)\ensuremath{\sim}39\mathrm{T},$ and the out-of-plane superconducting coherence length ${\ensuremath{\xi}}_{c}(0)\ensuremath{\sim}28\AA{}.$ Based on the similarities between these ruthenates and the superconductor ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}},$ we estimated ${H}_{c2}^{c}(0)\ensuremath{\sim}8\mathrm{T}$ and ${\ensuremath{\xi}}_{\mathrm{ab}}(0)\ensuremath{\sim}140\AA{}.$ We used these parameters to discuss the coexistence of long-range magnetic order and superconductivity on a microscopic scale on these materials.

We have performed a detailed characterization of the magnetic properties of Ni nanoparticles embedded in a SiO2 amorphous matrix. A modified sol-gel method was employed which resulted in Ni particles with average radius ;3 nm, as inferred by TEM analysis. Above the blocking temperature TB’20 K for the most diluted sample, magnetization data show the expected scaling of the M/ MS vs H/T curves for superparamagnetic particles. The hysteresis loops were found to be symmetric about zero field axis with no shift via exchange bias, suggesting that Ni particles are free from an oxide layer. For T,TB the magnetic behavior of these Ni nanoparticles is in excellent agreement with the predictions of randomly oriented and noninteracting magnetic particles, as suggested by the temperature dependence of the coercivity field that obeys the relation HC(T)5HC0@12(T/TB) 1/2 # below TB with HC0;780 Oe. The obtained values of HC0, considering the temperature dependence of the magnetic anisotropy constant, are discussed within the scenario of isolated randomly oriented and noninteracting single-domain particles.

Polycrystalline samples of PrBa2Cu3O7– y were prepared through two different routes: (a) mixing Pr6O11, BaCO3, and CuO; (b) sol-gel precursors. The samples were heat-treated in the temperature range 700 ~ 11.88 Å. Oxygenated PrBa2Cu3O7-y samples were found to have an orthorhombic structure with lattice parameter c ranging from 11.72 to 11.75 Å. Electrical resistivity rho(T) measurements performed on these compounds revealed a semiconductor-like behavior in the temperature range 77 ~ 17 K. Evidence of super-conductivity was not observed on our samples, in agreement with most of the results reported in the literature.

Esta tese apresenta um estudo sistemático da síntese e das propriedades físicas de amostras policristalinas de Nd IND. 1-X R IND. X NiO IND. 3; R = Sm, Eu, 0 < OU = X < OU = 1. Estes materiais apresentam uma transição de fase metal-isolante MI em temperaturas 200 < OU = T IND. MI < OU = 400 K. Amostras foram produzidas a partir do método de precursores sol-gel, sinterizadas a 1000 GRAUSC e sob pressões de O IND. 2 de até 80 bar. O estudo da influência da substituição de R POT. 3+ na matriz de NdNiO IND. 3 foi realizado a partir das caracterizações através de medidas de difração de raios-X DRX, difração de neutrons como função da temperatura DRN, transporte elétrico ro(T), transporte térmico capa(T), coeficiente Seebeck S(T), calorimetria diferencial e susceptibilidade magnética qui(T). Os resultados de DRX revelaram que as amostras são monofásicas e cristalizam-se na estrutura perivskita distorcida ortorrombicamente, grupo espacial Pbnm. As medidas de DRN realizadas nas amostras de Nd IND. 1-XEu IND. X NiO IND. 3 mostraram a evolução dos parâmetros de rede e do volume da cela unitária V como função da temperatura. Estas caracterizações revelaram que, em T DA ORDEM DE T IND. MI, ocorre uma expansão em V, assim como um aumento do ângulo de ligação Ni-O e uma diminuição do ângulo de \"superexchange\" teta. Medidas de ro(T) revelam a ocorrência da transição MI em um amplo intervalo de temperatura 200 < OU = T IND. MI 400 K. Através destas medidas verificou-se também a presença de histerese térmica ocorre decresce continuamente com o aumento de x, até anular-se em x > 0,5 e em x > 0,35 para R=Sm e Eu, respectivamente. Este resultado foi confirmado através das medidas de capa(T) e S(T). Além disso, verificou-se a importância da contribuição da rede na capa(T). As medidas de S(T) indicam que os portadores de carga são elétrons e que a densidade de ) estados no nível de Fermi N(E IND. F) foi estimada ser da ordem de 10 POT. 23 (eVcm POT. 3) POT. -1. Os valores de T IND. MI e a presença ou não de histerese térmica foram verificados através das medidas de DSC. Um estudo foi feito para verificar qual a maneira mais precisa de subtrair a contribuição dos íons terras-raras nas medidas de susceptibilidade magnética qui(T) dos compostos Nd IND. 1-X R IND. X NiO IND. 3. Após estas correções foi possível verificar o ordenamento magnético da sub-rede do Ni POT. 3+ na região de temperatura T IND. n DA ORDEM DE 200 K para as amostras com x < 0,4 e x < 0,25 para R=Sm e Eu, respectivamente. Ajustes lineares feitos em qui(T) acima de temperaturas T > 200 K revelaram valores de momentos magnéticos efetivos müeff variando de 1,7 a 1,8 mü IND. B o que está em concordância com o valor esperado de müeff DA ORDEM DE 1,76 mü IND. B do íon livre de Ni POT. 3+. Adicionalmente, uma separação precisa do termo independente da susceptibilidade magnética foi efetuada e a susceptibilidade de Pauli dos materiais foi encontrada. Foi possível então obter uma estimativa da densidade de estados no nível de Fermi N(E IND. F), que gerou valores similares aos obtidos via medidas do coeficiente Seebeck. Entretanto, o comportamento de qui(T) corrigido abaixo de T IND. n revelou características de um antiferromagnetismo não convencional devido a um aumento monotônico de qui(T) com o decréscimo da temperatura e a presença de irreversibilidade nas curvas resfriadas a campo magnético zero ZFC e do refinamento de estrutura estimou-se que a valência no Ni nas amostras de Nd IND. 1-X R IND. X NiO IND. 3 DA ORDEM DE 3. Estimativas grosseiras da largura de bando W do O 2ro e da energia de transferência de carga delta para a série de compostos Nd IND. 1-X R IND. X NiO IND. 3 revelaram valores compatíveis com aqueles ) encontrados na literatura. De maneira geral, as caracterizações das propriedades estruturais, de transporte e magnéticas sugerem que os compostos Nd IND. 1-X R IND. X NiO IND. 3 podem ser classificados como sistemas onde correlações eletrônicas e flutuações dessas correlações ocorrem. Foram discutidas algumas limitações acerca da aplicabilidade dos modelos vigentes para a explicação da transição metal-isolante nos niquelatos aqui estudados. This work reports a systematic study on the synthesis and general physical properties of polycrystalline samples of Nd IND. 1-X R IND. X NiO IND. 3; R = Sm, Eu, 0 < OU = X < OU = 1. These compounds exhibit a metal-insulator MI phase transition in a broad range of temperature 200 < OU = T IND. MI < OU = 400 K. The samples were prepared through sol-gel precursors and sintered at extreme conditions: high temperatures 1000 GRAUSC and under oxygen pressures up to 80 bar. These samples were characterized by several techniques including X-ray powder diffraction XRD, neutron diffraction as a function of temperature NRD, electrical resistivity ro(T), thermal conductivity capa(T), Seebeck coefficient S(T), differential scanning calorimetry DSC, and magnetic susceptibility qui(T). The results of XRD revealed that all samples are single phase and crystallize in an orthorhombic structure, space group Pbnm. The NRD data, combined with the Rietveld analysis, indicated small changes in the lattice parameters a, b, and c and in the volume V of the unit cell T DA ORDEM DE T IND. MI. Such a small change in these parameters is accompained by either a little decrease of the superexchange angle teta and a small expansion of the Ni-O bond-length. The ro(T) data exhibit interesting features such as: (1) a metallic-like behavior of ro(T) at high temperatures; (2) a huge increase of the magnitude of ro(T) at T DA ORDEM DE T IND. MI; and (3) a thermal hysteresis occurring just below T DA ORDEM DE T IND. MI in a temperature interval as large as 100K. Such a thermal hysteresis is characteristic of a first order MI transition and was found to vanish with increasing substitution of x. This strongly suggests that increasing x modify the character of this transition to second order. Thermal properties were carried out and confirmed the change of this MI transition with increasing x. In addition, an analysis of the capa(T) data indicate that phonons are the major thermal carriers in these nickelates. Also, the Seebeck coefficient S(T) data revealed features of a conventional metal at higher temperatures with electrons as carriers. An accurate analysis of the S(T) data based on simple band structure arguments indicate a density of states at the Fermi level of 10 POT. 23 (eVcm POT. 3) POT. -1 and energy gaps in the insulating regime close to 20 meV. The character of the first order transition in lightly substituted samples at T DA ORDEM DE T IND. MI was also inferred from the DSC data. The S(T) data confirmed the occurrence of the metal-insulator transition and the already observed change from first to second order character with increasing x. The magnetic susceptibility ípsilon(T) data have been precisely corrected by a systematic subtraction of the R POT.3+-ion contribution of the measured qui(T). Linear adjusts of the corrected curves above 150K where found to fit the Curie-Weiss law with effective magnetic moment of mü IND. EFF ~ 1.76 mü IND. B, which is close to the free-ion value of mü IND. EFF ~ 1.76 mü IND. B (Ni POT. 3+). These results indicate that the Ni POT. 3+ array displays an antiferromagnetic ordering below a well-defined temperature T IND. N, which is close to T IND.MI for Nd IND. 1-X R IND. X NiO IND. 3 and lightly substituted samples. However, the evolution of the susceptibility of the Ni POT. 3+ array displays features which are fingerprints of unconventional antiferromagnetic state. These features, observed mostly below T IND. N, include a field independent irreversibility of qui(T) and a systematic increase of qui(T) with decreasing temperature, resembling that of a paramagnet. An analysis of the electronic contribution to ípsilon(T) resulted in a density of states at the Fermi level close to the one estimated from the S(T) data. These results are discussed within the context of recent experimental results and theories employed to explain the origin of the metal-insulator transition in these nickelates.

A modified sol-gel technique was used to synthesize nanocomposites of Ni:SiO2 which resulted in Ni nanoparticles embedded in a SiO2 amorphous matrix. Transmission electron microscopy TEM analysis were performed to study the structure and morphology of the magnetic powders. The Ni particles were found to have a good dispersion and a controlled particle size distribution, with average particle radius of ∼ 3 nm. A detailed characterization of the magnetic properties was done through magnetization measurements M(T,H) in applied magnetic fields up to ± 7 T and for temperatures ranging from 2 to 300 K. The superparamagnetic (SPM) behavior of these metallic nanoparticles was inferred from the temperature dependence of the magnetization. The blocking temperature TB, as low as 20 K, was found to be dependent on Ni concentration, increasing with increasing Ni content. The SPM behavior above the blocking temperature TB was confirmed by the collapse of M/MS vs. H/T data in universal curves. These curves were fitted to a log-normal weighted Langevin function allowing us to determine the distribution of magnetic moments. Using the fitted magnetic moments and the Ni saturation magnetization, the radii of spherical particles were determined to be close to ∼ 3 nm, in excellent agreement with TEM analysis. Also, magnetic hysteresis loops were found to be symmetric along the field axis with no shift via exchange bias, suggesting that Ni particles are free from an oxide layer. In addition, for the most diluted samples, the magnetic behavior of these Ni nanoparticles is in excellent agreement with the predictions of randomly oriented and noninteracting magnetic particles. This was confirmed by the temperature dependence of the coercivity field that obeys the relation HC(T) = HC0 [1-(T/TB)1/2] below TB with HC0 ∼ 780 Oe.

Pre-reacted powders of (Bi-Pb)2Sr2Ca2Cu3O10+δ (Bi-2223) were consolidated by using the spark plasma sintering (SPS) technique under vacuum and at different consolidated temperatures TD. We have found that the transport properties of SPS samples depend on their oxygen content because the SPS process is performed under vacuum. From these results we have inferred that SPS samples are oxygen deficient and that a post-annealing treatment, performed in air for a brief time interval, is needed to restore such a deficiency. Measurements of temperature dependence of the thermal conductivity, κ(T), were performed in all SPS samples including a reference sample sintered at 845 °C in air. The results indicate that the electronic contribution to the thermal conductivity in all samples is very low. Values of κ were found to be higher in SPS samples mostly because of their high volume density of ~ 5.7 g/cm3. We have also performed measurements of the critical current density as a function of the applied magnetic field, Jc(Ba). All samples display a clear Josephson-like behavior and low values of the superconducting critical current density at zero applied magnetic field. The experimental results indicate that the oxygen deficiency in SPS samples is marked near the grain boundaries. This suggests the occurrence of grains with core-shell morphology, where the width of the shell is consolidation temperature dependent.

Amostras policristalinas de \'Pr\'\'Ba IND. 2\' \'Cu IND. 3\' \'O IND. 7-y\' foram produzidas através de duas rotas diferentes: (i) mistura estequiométrica de óxidos e carbonatos de Pr, Ba e Cu; e (ii) através do método de precursores sol-gel. A investigação da cinética de formação destes compostos, feita através de medidas de difração de raios-X DRX, mostrou que a fase pretendida pode ser obtida através de tratamentos térmicos em temperaturas da ordem de 810 \'GRAUS\'C e em atmosfera inerte quando os materiais são provinientes de precursores sol-gel. Para tratamentos térmicos por intervalos de tempos da ordem de 50 h, o material obtido é de fase única, apresenta estrutura tetragonal, é altamente cristalino e com um parâmetro cristalográfico c robusto. Essas características sugerem que a possível ocupação de íons \'Pr POT. +3\' nos sítios de \'Ba POT. +2\', vice-versa, é inibida para este tipo de atmosfera. Tratamentos térmicos de oxigenação em temperaturas 300 \'GRAUS\'C < OU =\' T \'< OU =\' 400 \'GRAUS\'C, promoveram a evolução do caráter artorrômbico do material e a diminuição do parâmetro de rede c. Medidas de resistividade elétrica como função da temperatura mostraram comportamento do tipo semicondutor para todas as amostras oxigenadas. Medidas de magnetização M (T) revelaram um comportamento paramagnético com uma forte contribuição do campo elétrico cristalino (CEF) para todos os materiais. Nenhuma evidência de supercondutividade pode ser observada em diversos materiais produzidos neste trabalho Preparation and characterization of \'Pr\'\'Ba IND. 2\' Cu IND. 3\' THE IND. 7-y\'

CuO nanograins (NGs) and CuO nanowires (NWs) on the top of nanograins samples were produced by the electrical resistive heating method. The NGs sample shows absence of long range magnetic order and strong field-induced ferromagnetic behavior. In the sample comprised of NWs on the top of NGs, a long-ranged antiferromagnetic ordering is induced by a magnetic field of 5 kOe and coexists with an enhanced ferromagnetic-like contribution. The ferromagnetic behavior is observed below and above the temperature-induced TN suggesting that this behavior is not dependent on the original magnetic state of the system, whether it is paramagnetic (PM) or antiferromagnetic.

We report on transport properties of granular Sm 1.83 Ce 0.17 CuO 4− y superconductors belonging to the dielectric side of the superconductor–insulator transition. This compound has a small superconducting volume fraction and can be described by a collection of superconducting islands embedded in an insulating matrix. We have performed measurements of magnetoresistance, R ( T , H ), in applied magnetic fields up to 17 T, and Seebeck coefficient measurements, S ( T , H ), under applied magnetic fields to 1 T. The magnetoresistance curves showed a clear upturn in the magnitude of R ( T , H ) below T ci ∼17.5 K and presents a change in the temperature dependence at T ∼11 K. S ( T , H ) curves also display well-defined changes at T ∼18 and T ∼10 K. These results are discussed within the scenario of a superconductor–insulator transition.

We have measured the temperature dependence of the electrical resistivity ρ ( T , B a ) in polycrystalline Bi 1.65 Pb 0.35 Sr 2 Ca 2 Cu 3 O y superconductors under two conditions: B a =0 and B a =43 mT, where B a is the applied magnetic field. Powders of this material were uniaxially pressed at 217 MPa and thermally treated to obtain cylindrical samples with similar dimensions. The physical properties of the two interfaces of these samples were investigated: the first, where the piston used in the compacting process has a direct mechanical contact with the powders, referred to as A, and the other one, which is parallel to the former, referred to as B. We have found appreciable differences in the degree of texture between these faces from X-ray diffractometry. For transport measurements, two specimens with slab form were cut from the same sample. The first was extracted from the face A and the second one was cut along the thickness of the samples, from the face A to B. The temperature dependence of the electrical resistivity at zero applied magnetic field shows similar values of the critical temperatures in both samples, but appreciable difference in the offset temperatures was observed when a magnetic field of 43 mT is applied. These features are discussed assuming an inhomogeneous distribution of uniaxial compacting pressure in these ceramic samples.

We carried out an investigation of the magnetic and superconducting properties of Ru 1 − x Ir x Sr 2 GdCu 2 O 8 compounds for Ir concentrations up to x =0.25, which is the limit of solubility. This study consisted in the X-ray diffraction analysis of these materials, and the measurements of the temperature dependence of the electrical resistivity, and of the ac and dc magnetic susceptibilities. The substitution of Ir for Ru moves the magnetic transition of the Ru-sublattice near 130 K to lower temperatures, and it suppresses superconductivity fairly rapidly. The zero-resistance state drops from ∼32 K for the pure Ru-1212 compound to ∼13 K for x =0.10. Further addition of Ir causes a gradual evolution from metallic to non-metallic behavior, with progressively larger upturns at low temperatures.

The effects of uniaxial and isostatic compacting pressures on the superconducting critical current density J c ( B a ) dependence under low applied magnetic fields ( B a 1.65 Pb 0.35 Sr 2 Ca 2 Cu 3 O y . Two batches of this material were made and pelletized by using different procedures. One of them was pressed uniaxially and the other one isostatically under pressures ranging from 100 to 300 MPa before the last heat treatment. X-ray diffraction patterns revealed that increasing compacting pressure results in an improvement of the grain alignment which is more pronounced in samples subjected to uniaxial pressure. The superconducting critical current density in zero applied magnetic field J c (0) in both batches was found to increase with increasing compacting pressure. However, samples subjected to uniaxial pressure show J c (0) values over four times higher than those pressed isostatically. In addition, the J c ( B a )/ J c (0) ratio for these batches was found to be very similar: it exhibits a clear Josephson-like behavior at low compacting pressure, which changes to a more magnetic field independent behavior at higher compacting pressures. The experimental results are interpreted in terms of changes in the pinning energy and grain alignment with increasing compacting pressure.

A fundamental theoretical characterization of a many-body system such as that defined by the Hubbard Hamiltonian is the single particle Green’s function G. Single particle electron spectroscopies provide a means to measure the spectral weight of G and so these spectroscopies are in principle a very powerful experimental means of testing theoretical predictions for the Hubbard model. This article gives an overview of problems and opportunities associated with the application of electron spectroscopy to this problem.

The spark plasma sintering (SPS) technique, by using a compacting pressure of 50 MPa, was used to consolidate pre-reacted powders of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223). The influence of the consolidation temperature, TD, on the structural and electrical properties has been investigated and compared with those of a reference sample synthesized by the traditional solid-state reaction method and subjected to the same compacting pressure. From the X-ray diffraction patterns, performed in both powder and pellet samples, we have found that the dominant phase is the Bi-2223 in all samples but traces of the Bi2Sr2CaCu2O8+x (Bi-2212) were identified. Their relative density were ∼85 % of the theoretical density and the temperature dependence of the electrical resistivity, ρ(T), indicated that increasing TD results in samples with low oxygen content because the SPS is performed in vacuum. Features of the ρ(T) data, as the occurrence of normal-state semiconductor-like behavior of ρ(T) and the double resistive super...