摘要:

The surface and interface electronic structure of mismatched InxAl1−xAs epitaxial layers grown by molecular beam epitaxy on InP have been investigated using surface photovoltage spectroscopy. The crystalline structure of the epilayers was also examined by double‐crystal x‐ray diffraction. For coherently strained layers, only a few gap states are identified. Highly strained samples with inferior crystalline quality, as judged by a broadened x‐ray diffraction peak and the absence of Pendellosung fringes, display a rich spectrum of states in the band gap. Some of the states are close to the surface while others are located in the vicinity of the InAlAs/InP heterointerfaces. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360425

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effect of metal sheet resistance on capacitance measurements of Schottky barriers is investigated through modelling. The calculations show that when the capacitance is determined by conventional ac impedance measurements, the value obtained is less than the true capacitance when the metal sheet resistance is high. The 1/C2versusVplot will be nonlinear for extreme cases, but remains linear even for metal films with quite high resistivities. In the linear regime, the curves for different resistances will have a near identical slope but will be shifted along the 1/C2axis. This causes the barrier height to be overestimated. The error increases with increasing metal resistances. The series resistance determined fromI‐Vplots may not necessarily indicate whether the metal sheet resistance is detrimental for capacitance measurements. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360688

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The hypothesis of charge‐transfer to the cuprate‐planes, which lies at the foundation for most theories on high‐temperature superconductivity, is re‐examined in light of recent neutron‐diffraction data for La2−&bgr;Sr&bgr;CuO4and Nd2−zCezCuO4. The data indicate that the cuprate‐planes do not acquire holes as the materials become superconducting, and that the superconductingp‐type regions of the unit cells are in the noncuprate‐plane charge‐reservoir layers instead. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360426

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Superconducting YBa2Cu3O7−xfilms having smooth surfaces were successfully synthesized by a microwave plasma‐enhanced pulsed laser deposition (PEPLD) process. Particulates that frequently occurred in films grown by the conventional PLD process were effectively eliminated. The films were epitaxial‐like. Thec‐axis was perpendicular to the films’ surface, theaandbaxes were aligned in the films’ plane, and the onset and zero of the transition temperature were atTc=90 K andTc0=86 K, respectively. Optical emission spectroscopy indicated that the presence of oxygen plasma not only reexcited the laser‐induced species via the collision process, but also produced abundant atomic oxygen in PEPLD process. The surface reaction kinetics for the formation of the thin‐film process was thus greatly enhanced, which substantially improved the thin‐film quality. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360427

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

TlBa2CaCu2O7(Tl‐1212) superconducting films 5000–6000 A˚ thick have been grown on LaAlO3(100) substrates using oxide precursors in a closed two‐zone thallination furnace. Tl‐1212 films can be grown with transition temperatures ∼100 K, and critical current densities measured by magnetization ofJcm(5 K)≳107A/cm2andJcm(77 K)≳105A/cm2. Processing conditions, substrate temperatures and Tl‐oxide source temperatures are found which result in smooth, nearly phase‐pure Tl‐1212 films. Variations in the respective temperature ramps of the Tl‐oxide zone and the substrate zone can greatly influence resulting film properties such as microstructure, morphology, superconducting transition temperature, and critical current density. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360428

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Presented is a novel high sensitivity magnetometer allowing us to measure the magnetization reversal of about 104&mgr;Bcorresponding to a sensitivity of about 10−16emu. The detector is a niobium micro‐bridge DC superconducting quantum interference device (SQUID), fabricated using electron‐beam lithography. It is operational in the temperature range of 0–7 K. Furthermore, we present a method to deposit on the SQUID loop a small number of Co clusters of about 2–5 nm in diameter. The first results obtained on these samples show that there is still a ferromagnetic coupling between the clusters and the magnetization reversal takes place by small avalanches. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360429

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Neutron diffraction has been used to determine the location and concentration of C in Nd2Fe17and in a Si substituted alloy. The results indicate that two carbide phases exist. One contains nearly three C atoms per formula unit, while the other has a much lower concentration. The high C phase contains C only on the 9esites, but the low C phase appears to contain C on the tetrahedral 18gsite. The changes in interatomic distances and cell volume are associated with the different site occupancies. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360726

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The interpretation of experiments on the effect of interface intermixing on the giant magnetoresistance (GMR) effect in antiferromagnetic‐coupled multilayers can be complicated by the fact that interface intermixing also changes the coupling strength; therefore, we have grown an artificially intermixed region in Co/Cu spin valves with uncoupled Co layers. The structure we used was a newly engineered spin valve composed of 100 A˚ Co+6 A˚ Ru+25 A˚ Co+40 A˚ Cu+100 A˚ Co. Here the Ru layer provides an antiparallel alignment of the Co layers and the Cu layer decouples the upper two Co layers. An intermixed CoCu region has been grown at the Cu/Co interface and in some cases also at the Co/Cu interface by alternately sputtering 1 A˚ Co and 1 A˚ Cu. X‐ray measurements confirm the existence of an intermixed region, although no reduction of magnetic moment is observed as is reported for homogeneous sputtered Co0.5Cu0.5alloys. This indicates the existence of Co clusters in the intermixed regions. There is no difference in GMR between an intermixed layer of thicknesstat one Co/Cu interface or two intermixed layers of thicknesst/2 at both Co/Cu interfaces. Thus, it seems that the total thickness of the intermixed regions is decisive for the magnitude of the GMR. BecauseG, &Dgr;G, and &Dgr;G/Gapall show a gradual decrease when the nominal thickness of the intermixed region increases from 0 to 36 A˚, this indicates that there is no strong spin‐dependent scattering in this region. This is in agreement with calculations on a model bilayer Co/Cu/Co with the Camley–Barnas model. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360430

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have studied the process by which the in‐plane magnetization of an ultrathin (4–11 ML) epitaxial iron film reverses under the action of an external magnetic field. Kerr effect measurements reveal a small in‐plane uniaxial anisotropy superimposed on the cubic magnetocrystalline anisotropy which greatly influences the reversal. In addition, we find that depending upon the field orientation, reversal can proceed either via a ‘‘1‐jump’’ mechanism, by the sweeping of 180° domain walls and which gives a classic square hysteresis loop, or by a ‘‘2‐jump’’ mechanism, by the sweeping of 90° domain walls at two distinct applied field strengths—this gives a more unusual hysteresis loop with two irreversible transitions. We have developed a simple phenomenological energy model which explains how so small a uniaxial anisotropy can play so significant a role in the reversal process. The model explains the two reversal mechanisms and predicts with good experimental agreement which should be observed for different applied field orientations. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360431

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We solve numerically the Landau‐Lifshitz‐Gilbert equation and calculate the magnetization in a magnetic film including a nonmagnetic defect for two initial magnetization states consisting of circular structure with 4 domains and 7 domains. The defect at the vortex wall restrains the magnetization temporarily but the vortex wall comes out of the defect beyond a critical applied field. This critical field increases as the defect size becomes large. The defect at the film side fixes the magnetization at the film edge. The edge defect leads to a reproducible magnetization state inside the film, though a locally stable structure appears for the magnetic thin film without defects. It seems that the defect may improve the stability of the magnetic thin film head. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.360432

出版商:AIP    

年代:1995

数据来源: AIP