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In this article, we investigate extensively the bipolar-switching properties of Al2O3- and HfO2- based resistive-switching memory cells operated at low current down to <1 μA. We show that the switching characteristics differ considerably from those typically reported for larger current range (>15 μA), which we relate as intrinsic to soft-breakdown (SBD) regime. We evidence a larger impact of the used switching-oxide in this current range, due to lower density of oxygen-vacancy (Vo) defects in the SBD regime. In this respect, deep resetting and large memory window may be achieved using the stoichiometric Al2O3 material due to efficient Vo annihilation, although no complete erasure of the conductive-filament (CF) is obtained. We finally emphasize that the conduction may be described by a quantum point-contact (QPC) model down to very low current level where only a few Vo defects compose the QPC constriction. The large switching variability inherent to this latter aspect is mitigated by CF shape tuning through adequate engineering of an Al2O3\HfO2 bilayer. [ABSTRACT FROM AUTHOR]

Applying a cost-effective process with a simple one-side-heating furnace, two layers of YBa2Cu3Ox (YBCO) bulks were successfully grown in one batch by using NdBa2Cu3Ox (NdBCO) thin-film-seeds deposited on MgO substrates. Due to the large temperature difference between the two layers, the seed-induced growth began at the bottom layer much later than that at the top layer. Remarkably, NdBCO films on the bottom layer samples survived a long time (over 15 h) above the growth temperature and effectively induced the YBCO growth. The significant thermal stability of the films, i.e., the tolerance for a long holding time on the surface of the molten pellet, is supposed to relate to a competition between the dissolution/diffusion of film materials into the liquid and NdBCO grain coarsening/Nd-YBCO crystallization. [ABSTRACT FROM AUTHOR]

The effect of oxygen partial pressure on the thermal stability of Nd-123 superconductor thin films was investigated by means of high temperature in situ microscopy. It was found that the thermal stability of Nd-123 films decreases as the oxygen partial pressure increases. We attribute the thermal stability suppression to the increased growth rate of Nd-422 and a high concentration difference ratio. Under the assumption of quasi-equilibrium, a simplified model for peritectic melting of RE-123 was suggested. [ABSTRACT FROM AUTHOR]

From the low-temperature (down to 10 K) dc-magnetization data of the La0.7Sr0.3MnO3 (LSM), La0.7Ca0.3MnO3 (LCM), and Pr0.7Ca0.3MnO3 (PCM) systems, we estimated the critical exponents β, γ, and hence δ from the analysis of the modified Arrot plots. The exponent β estimated for the LCM system is less than that predicted by Heisenberg model and resides within the zone predicted by Ising model while for the LSM sample, β is higher than that predicted from the Heisenberg model which is considered to be due to the presence of dipole-dipole interaction arising from the large spin moment in the LSM system. The magnetization data of the PCM system cannot be fitted to the modified Arrot plots, which suggest highly inhomogeneous ground state even under 5 T magnetic field. Both LSM and LCM have almost equal values of γ. Seebeck coefficient data indicate a crossover from higher-temperature n-type to lower-temperature p-type conductivity behavior in both LSM and LCM systems, while the semiconducting PCM system shows p-type conductivity throughout the temperature range (300–80 K). It is noticed that for LSM system TC (Curie temperature) and TMI (metal-insulator transition temperature) are almost equal (∼360 K), whereas for the LCM system there exist a large difference between TC and TMI (TC∼245 K and TMI∼265 K), which may give some idea regarding the critical behavior of the respective samples. [ABSTRACT FROM AUTHOR]

Transport properties (resistivity and thermoelectric power) of Pb doped LaNiO3 viz. La1-xPbxNiO3-δ (0.0<=x<=0.1) show metallic behavior over a wide range of temperature (10–550 K). Pb doping (up to 10%) at the La site does not destroy the metallic behavior of LaNiO3. The paramagnetic susceptibility χ decreases with Pb doping. Above 50 K, χ is almost temperature independent and exhibits Pauli like features with a small additional Curie law contribution. The resistivity ρ increases with Pb doping though the thermoelectric power does not change proportionately, indicating that Pb doping does not introduce much disorder in the system. A linear T dependence of ρ observed above 150 K suggests the importance of electron–phonon (el–ph) interactions but at temperature below 150 K, ρ follows a T1.5 dependence. The estimated el–ph interaction constant λ increases (0.80–2.53) with Pb doping (x=0.0–0.1). No saturation of resistivity has been observed even up to 550 K with x<=0.1. The phonon frequency νph∼3444 cm-1 of the undoped sample calculated from the absorption peak of the Fourier transform infrared spectra agrees well with that at ∼3025 cm-1 estimated from the reported heat capacity data. [ABSTRACT FROM AUTHOR]

Hydrostatic-pressure (up to 0.96 GPa) dependence of Tc in a newly discovered Fe-based superconductor (Tl0.59Cs0.26)Fe1.9Se2 (Tc = 28 K, at ambient pressure) is reported. Static magnetization measurements under pressure indicate that the linear increase in Tc is initially rapid (dTc/dP ∼ 9.9 K · GPa-1) but slows down to dTc/dP ∼ 2.5 K · GPa-1 for P ≧ 0.18 GPa. The Tc of the superconducting phase is 32 K at pressure P = 0.96 GPa. The simple rigid band model or the Bardeen, Cooper, Schrieffer theory may not be sufficient to account for our observations, if one assumes that the lattice parameters would be linearly decreased with pressure. [ABSTRACT FROM AUTHOR]

The magnetic-induced dielectric responses of BiFeO3 (BFO) thin films were measured at the X-band microwave frequency ranged from 7 to 12.5 GHz. The measurement was given initially by a high-precision cavity microwave resonator without magnetic field. Both the real and imaginary parts of the permittivity showed its dielectric property as a function of the measuring frequency. The X-band dielectric responses of the BFO thin film were then measured by a controlled magnetic field at room temperature. The data demonstrated up to 2.2% dielectric tunability by using only 3.46 kOe magnetic field at TE107 mode (9.97705 GHz). [ABSTRACT FROM AUTHOR]

Low temperature calorimetric measurements have been made on a series of binary aluminum alloys containing 1–10 at. % lithium. The heat capacity data are analyzed in terms of an electronic and a lattice contribution. Accordingly, the low level of lithium addition yields appreciable changes in the electronic density-of-states at Fermi level and the characteristic Debye temperature of lattice. These results reflect certain degrees of electron localization between aluminum and lithium atoms, providing a fundamental basis for solid solution strengthening in the lightweight materials with great potential in aerospace applications. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the variations of the electrical resistivity, the magnetization and the grain-boundary precipitates of a nickel-rich nickel-indium alloy system. Experimental procedure; Results and discussion.

Investigates the variations of the grain-boundary precipitates, the electrical resistivity and the magnetization of a Ni-8 at. tin alloy as functions of annealing temperature and annealing time. Preparation of the alloys; Microscope used to observe the grain-boundary precipitates; Information on the magnetization of the homogenized sample.

Presents a study on the influence of crystal structure on the magnetoresistance of cobalt (Co)/chromium (Cr) multilayers. Characteristics of epitaxial Co/Cr multilayers; Definition of the giant magnetoresistance in multilayers; Effects due to the spin dependent scattering at the interfacial regions of the superlattice.

Presents a study which examined the optical, electrical and magnetic properties of neodymium iron boron films. Experimental methods; Observations of the oscillatory behavior with thickness of the films; Anomalous behaviors near the Curie temperature.