摘要:

We have calculated the initial magnetization curves and hysteresis loops for hard type‐II superconductors based on the exponential‐law model,Jc(Hi) =k exp(−‖Hi‖/H0), wherekandH0are constants. After discussing the general behavior of penetrated supercurrents in an infinitely long column specimen, we define a general cross‐sectional shape based on two equal circles of radiusa, which can be rendered into a circle, a rectangle, or many other shapes. With increasing parameterp(=ka/H0), the computedM‐Hcurves show obvious differences with those computed from Kim’s model and approach the results of a simple infinitely narrow square pulseJc(Hi). For high‐Tcsuperconductors, our results can be applied to the study of the magnetic properties and the critical‐current density of single crystals, as well as to the determination of the intergranular critical‐current density from magnetic measurements.

ISSN:0021-8979    

DOI:10.1063/1.345355

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

X‐ray and ultraviolet photoelectron spectroscopies have been used to investigate the interaction between silicon and Bi2Sr2CaCu2O8+&dgr;highTcsuperconducting material. For low coverages, silicon adatoms disrupt CuO bonds and SrO bonds to form a complex Sr‐Si‐O phase. This interlayer efficiently prevents further reaction between silicon and the Bi2Sr2CaCu2O8+&dgr;superconductor.

ISSN:0021-8979    

DOI:10.1063/1.345330

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The Bi‐based oxide superconducting tapes containing high‐Tc(Tc=110 K) and low‐Tc(Tc=85 K) phases were prepared by the powder metallurgy method using an Ag sheath, andJcwas measured at 77 and 4.2 K in magnetic fields up to 30 T. A grain‐oriented microstructure with thecaxes perpendicular to the tape surface was obtained for the tapes with a high‐Tcphase by applying a combination of cold rolling and sintering.Jcof the high‐Tctape was significantly improved by this grain orientation. However, large anisotropy inJcwith respect to the magnetic field direction was observed for these textured tapes. For the low‐Tctapes, it was difficult to obtain a grain‐oriented microstructure by the cold rolling and sintering process. However,Jcat 4.2 K of the nontextured low‐Tctape is as high as that of the grain‐oriented high‐Tctape. TypicalJcvalues at 4.2 K were above 104A/cm2at 12 T for both high‐ and low‐Tctapes.Jcat 4.2 K of the Bi‐based tapes is much less sensitive to the magnetic field than the conventional metallic superconductors, which indicates that the Bi‐based oxide is a good candidate for the high‐field superconducting magnet.

ISSN:0021-8979    

DOI:10.1063/1.345331

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Reliable critical current density measurements have been sucessfully carried out on superconducting thin films which wereinsitupatterned during the laser deposition process. This method does not require cumbersome wet etching or post‐ion‐implantation patterning steps for measuring transport critical current densities of thin films. Epitaxial films of YBa2Cu3O7on (100) SrTiO3and (100)yttria‐stabilized ZrO2(YSZ) were fabricated at low processing temperatures (500–650 °C) by the excimer laser ablation technique in an oxygen ambient coupled with a dc bias voltage of +300 V on an interposing ring between the substrate and the target. Steel masks of various lateral dimensions were placed close to the substrate to generate various patterns. The superconducting properties obtained at the masked and unmasked areas of the film were similar and reproducible. The thickness and width of the mask have been found to be critical in controlling the superconducting properties of the patterned thin films. Excellent quality superconducting thin films were obtained in the patterned areas. The critical temperature of the films was found to lie in the range of 88–90 K, and the best critical current density values (at 77 K and zero magnetic field) of 1.0×106, 5.0×106, and 6.5×106A/cm2were obtained for films deposited on (100) YSZ, (100) SrTiO3, and (100) LaAlO3, respectively.

ISSN:0021-8979    

DOI:10.1063/1.345332

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The formation of good quality epitaxialc‐axis‐perpendicular YBa2Cu3O7superconducting thin films on (100) yttria‐stabilized‐zirconia (YSZ) substrates in the temperature range of 550–650 °C by a biased laser deposition method is reported. However, below 550 °C, the epitaxial quality of the films decreased appreciably with corresponding changes in the superconducting properties. For temperatures much below the critical temperature, the critical current density showed a linear variation with temperature, with a value of 1.0×106A/cm2at 77 K and zero magnetic field. Because of the lattice mismatch between the substrate and the film, the interface was found to be highly strained in the presence of a large number of defects. The epitaxial nature and the crystalline quality of the films were determined by a number of techniques including Rutherford backscattering/channeling, electron channeling, cross‐section transmission electron microscopy (TEM), and x‐ray diffraction techniques. Rutherford backscattering channeling showed a minimum channeling yield of about 18%–25% for films deposited at and above 550 °C. Cross‐section TEM and x‐ray diffraction revealed the following thin film and substrate relationships: [001]film∥[001]YSZand [110]film∥[100]YSZ. The electron channeling pattern taken from a large area confirmed the epitaxial relationship. The lattice parameters mismatch in this orientation has been found to gives rise to stresses near the interface.

ISSN:0021-8979    

DOI:10.1063/1.345333

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thermally‐excited spin waves in double‐layer films of FeSi/X/FeSi (where X=ZnO and SiO2) have been studied by Brillouin scattering. The thickness of the FeSi (2.6 wt. % of Si) layers is fixed at 1100±30 A˚. Scattering from the Damon‐Eshbach‐type surface wave and the standing spin waves has been observed. The standing spin‐wave structure of a 28‐A˚‐thick SiO2spacer is modified by interlayer exchange coupling, but not that of a 5‐A˚‐thick ZnO spacer. The general trend of magnon frequencies as functions of the external magnetic field, the surface wave vector, and spacer thickness can be explained by the theory developed by Gru¨nberg [J. Appl. Phys.51, 4338 (1980)]. The Damon‐Eshbach‐type surface mode exhibits a systematic deviation from that theory at small surface‐wave vectors.

ISSN:0021-8979    

DOI:10.1063/1.345334

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This article uses a fully quantitative approach to describe the behavior of the minute tip of the magnetic force microscope (MFM) over longitudinally directed magnetic bits. Three possible magnetic structures are taken into consideration together with a realistic tip model. The magnetic and van der Waals interactions beween the tip and the sample are derived analytically to simulate a force gradient in MFM. The contours of the constant force gradient are presented and related to the known experimental data. The important role of the van der Waals force gradient in constant force gradient measurements is shown. The force gradient from a magnetic interaction is partly negative and partly positive and is balanced or increased by the (always positive) van der Waals force gradient. Force gradient asymmetry above the transition area is revealed when the MFM tip is tilted. By tilting the tip, the detection of two components of a stray field is accomplished. We found that the widths and heights of observed bumps of a force gradient depend on the width of the transition area and the deviation of the magnetization vector from the recording direction. These factors are especially important in determining what tolerance can be put on a read/write head’s performance. A lateral resolution of 90 nm could be achieved with our tip model.

ISSN:0021-8979    

DOI:10.1063/1.345335

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A convenient method is proposed for the analysis of the ionic thermocurrent data. Dielectric relaxation parameters in a number of cases have been evaluated following the suggested method of analysis. Evaluated parameters are found to be accurate. The correctness of the evaluated parameters has been checked through the retracing of the ionic thermocurrent spectrum.

ISSN:0021-8979    

DOI:10.1063/1.345336

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report photoluminescence measurements made on free‐standing, lattice‐matched GaAs/AlGaAs and pseudomorphic InGaAs/GaAs quantum boxes fabricated by laterally patterning quantum wells using electron‐beam lithography and either reactive ion etching or ion beam milling. At temperatures below 10–20 K the luminescence efficiency of most of the GaAs quantum‐box arrays tends to scale with the volume of quantum‐well material remaining after processing even for the smallest boxes which have lateral dimensions of only 40–50 nm. These observations indicate that the surface recombination rate in GaAs submicron structures can be small relative to the radiative recombination rate at low temperatures. In contrast, radiative recombination in the InGaAs/GaAs quantum boxes is strongly quenched for lateral dimensions less than 500 nm. We suggest that this is because photoexcited carriers are laterally localized in the GaAs boxes by potentials of the order of a few meV, possibly associated with interface disorder or strain relaxation, and that such localization effects are smaller in the InGaAs boxes.

ISSN:0021-8979    

DOI:10.1063/1.345337

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A computer simulation of small‐angle diffraction intensities is performed for a W/Si amorphous multilayer structure. The different models which are related to different interface structures after annealing are set up. Calculated results show that the existence of silicide interface layers which induces a change of both direction and magnitude of the diffraction amplitude is not always accompanied by a decrease of the diffraction intensity. In some cases, proper thickness and composition of interface layers may increase the diffraction intensity. However, the existence of systematic and random deviations of layer thicknesses always induces a decrease of x‐ray diffraction intensity.

ISSN:0021-8979    

DOI:10.1063/1.346089

出版商:AIP    

年代:1990

数据来源: AIP