摘要:

Crystallization of Bi2Sr2Ca1Cu2O8+&dgr;has been studied as a function of the partial pressure of oxygen, usinginsituhigh temperature x‐ray measurements, in order to determine the phases that form and the kinetics of growth. As the partial pressure of oxygen is systematically reduced, the dominant second phase changes from (Sr,Ca)2Cu1O3at 150 Torr of oxygen, to (Sr,Ca)1Cu1O2at 15 Torr of oxygen, to CaO in a pure nitrogen atmosphere. Normally, in 150 Torr of oxygen, Bi2Sr2Cu1O6+&dgr;is the first Bi cuprate to form from the melt but if the oxygen partial pressure is reduced to 75 Torr, then Bi2Sr2Ca1Cu2O8+&dgr;is favored due to the decreased amount of 2:1 phase in the melt.

ISSN:0021-8979    

DOI:10.1063/1.355009

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The probability of quasiparticle transmission going through a normal‐insulator‐ superconductor‐insulator‐normal (NISIN) geometry is theoretically calculated using Bogoliubov–de Gennes equations to investigate the feasibility of electron devices utilizing this geometry. This new calculation is able to include a current carried by Cooper pairs by employing hole injections from the outlet which destroy Cooper pairs at the outlet super‐ conductor‐insulator boundary. Resonant tunneling phenomena occur even if the electron kinetic energy is less than the superconducting energy gap and electron tunneling probabilities are greatly modified by the resonance. When the unevenness of the superconductor (S) width thickness is large compared with the electron wavelength in theSlayer, the resonance is smeared out in averaged tunneling probabilities. Then the tunneling probabilities can be controlled by the electron kinetic energy. Applications of the NISIN geometry for superconducting transistors are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.355010

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Many‐body effects in Cu 2px‐ray photoemission of Bi2Sr2CaxCu1+xO6+2x(x=0,1,2), La2−xSrxCuO4(x=0,0.13), and ErBa2Cu3O7−x,y(x<y) were observed and correlations between the many‐body effects and high‐Tcsuperconductivity of cuprate superconductors were reviewed. For the Bi2Sr2CaxCu1+xO6+2x(x=0,1,2) and La2−xSrxCuO4(x=0,0.13) systems, proper high‐Tcsuperconductivity was realized by increasing the transfer integral and the interaction strength of the Cu‐O bond of the crystal determined the superconducting properties. However, for the ErBa2Cu3O7−xand YBa2Cu3O7−xsystems, 90 K superconductivity was realized by increasing the charge transfer energy. The extended valence state including the Cu, Ba, and O valence states in the crystal determined the superconducting properties of the ErBa2Cu3O7−xand YBa2Cu3O7−xsystems.

ISSN:0021-8979    

DOI:10.1063/1.355011

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The photoresponses of Pb doped 2223 phase BiSrCaCuO films to low power 5 mm cw radiation were measured at temperatures nearTc. To identify the involved detection mechanisms, dependence of responsivity on temperature, supplied current, radiation power, and film granularity were investigated. At temperatures in the vicinity of the transition to the normal state, good agreement was obtained with the responses derived from a bolometric model. At temperatures below the transition, a nonbolometric response mode was found to occur when the film was biased into a partially resistive regime. Transient measurements were carried out showing a response time for this mode of at least 5 orders of magnitude smaller than that of the bolometric response. Further characteristics inherent to the nonbolometric mode include square law detection, nonlinear current dependence, and short wavelength cutoff. In addition, a correlation between responsivity and film granularity was established. For strongly granular films with an active area of 300×1800 &mgr;m2, a detectivityD* of about 1.1×108cm Hz1/2/W was typically achieved at a modulation frequency of 5 kHz. Consistency of the experimental results with the sub‐gap responses of Josephson arrays is discussed.

ISSN:0021-8979    

DOI:10.1063/1.355012

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Correlation studies between thin film nanostructure and macroscopic magnetic properties in ultrathin fcc Fe films grown epitaxially on room temperature Cu(100) substrates were performedinsituusing an ultrahigh vacuum scanning transmission electron microscope and the surface magneto‐optic Kerr effect. Nanometer lateral spatial resolution secondary electron microscopy revealed no gross morphological changes in the 2–10 monolayer thickness range. The use of broad‐beam Auger electron spectroscopy as an indicator of Cu surface cleanliness is shown to have insufficient sensitivity to detect surface contamination as evidenced by corresponding secondary electron micrographs. Cu(100) surfaces with both (nearly) perfect and imperfect surface structure, and identical Fe coverages, possess nearly identical polar and longitudinal Kerr hysteresis loops. Analysis of reflection high‐energy electron diffraction patterns confirms that Fe films grown on room temperature Cu(100) remain fcc with the same in‐plane lattice constant as the Cu template, for thicknesses up to 10 ML.

ISSN:0021-8979    

DOI:10.1063/1.354990

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An analysis of the micromagnetic structure of domains and domain walls in Co/Pt multilayer films is reported. Magneto‐optically written domains have been imaged in a scanning transmission electron microscope by using the modified differential phase contrast mode of Lorentz electron microscopy. These have been compared with computer‐simulated images based on a two‐dimensional model of a circular, perpendicular magnetized domain with a Bloch‐like wall structure. Agreement is found for the domain and stray field contrast, but the absence of wall contrast in the experimental images indicates a more complex wall structure in the multilayer than was assumed by the model. In a further series of calculations the magnetic microstructure of a Co/Pt multilayer was modeled by solving the Landau–Lifshitz–Gilbert equations. These suggest that the wall structure varies throughout the thickness of the multilayer, allowing significant saving of magnetostatic energy through the establishment of flux closure paths close to the walls, and are consistent with experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.354964

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

An analysis is presented of the detailed effects of varying the write parameters in Co/Pt multilayer films. Domains written thermomagnetically by laser modulation have been imaged using the modified differential phase contrast mode of Lorentz electron microscopy. The effects of different laser powers and bias fields were investigated. While the domain size increases with laser power, the bias field is found to have a profound effect on domain regularity. The periodicity of the irregular circumference of the domains written at high‐bias fields closely resembles the mean repeat in the ac‐demagnetized state suggesting that it arises as a relaxation phenomenon.

ISSN:0021-8979    

DOI:10.1063/1.354965

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The origin of the large perpendicular magnetic anisotropy (0.5–1×10−6erg/cm3) of Ni‐polyethelene coevaporated films has been studied. It is indicated that the anisotropy can be very well explained by uniaxial anisotropy induced by the large tensile stress (1–3×1010dyn/cm2) through the inverse magnetostrictive effect. Other factors, such as magnetocrystalline or shape anisotropy, produce little effect on the perpendicular anisotropy of the films.

ISSN:0021-8979    

DOI:10.1063/1.354966

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have investigated the growth conditions, the magnetic properties and low‐field ferromagnetic resonance (FMR) properties of praseodymium‐substituted garnet films. Films of general composition Y3−x−yPrxLuyFe5O12, were grown by liquid phase epitaxy onto [111]‐oriented Gd3Ga5O12substrates. Vibrating sample magnetometry, torque magnetometry and FMR were used to measure saturation magnetization and the cubic and induced anisotropy constants. It is shown that the uniaxial anisotropy constantKuand the first order magnetocrystalline anisotropy constantK1, have a strong dependence upon the praseodymium content. The addition of praseodymium in the garnet films improves the soft magnetic properties. The effect of the doping by praseodymium on the saturation magnetization is insignificant at room temperature. In‐plane coercivity is about 0.1 Oe.

ISSN:0021-8979    

DOI:10.1063/1.354967

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

In this study a systematic microstructural characterization of La‐modified lead zirconate titanate was carried out by hot‐ and cold‐stage transmission electron microscopy and selected area electron diffraction. The existence of 1/2[111] superlattice reflections (Fspots) became evident near 300 °C on cooling. The intensity of theFspots was found to increase with decreasing temperature, approaching a near constant intensity below 100 °C. In conjunction with compositional studies, it was proposed that theFspots arise from a doubling of the unit cell associated with a tilting of oxygen octahedra. The presence ofFspots at temperatures approaching the onset of local polarization was then interpreted as the existence of a hierarchy of domain states. This hierarchy was proposed to consist of an average‐cubic macroscopic structure containing rhombohedral micropolar regions on the scale of 50–100 A˚ that contain ferroelastic microtwins on the scale of several tens of angstroms.

ISSN:0021-8979    

DOI:10.1063/1.354968

出版商:AIP    

年代:1993

数据来源: AIP