摘要:

Nb/Al–AlOx–Nb/Al–AlOx–Nb double‐barrier three‐terminal Josephson devices with a thin middle Nb/Al bilayer, which have potential for use as switching and amplifying elements in superconducting electronics, have been investigated in the stationary state by means of low‐temperature scanning electron microscopy. For the devices with lateral sizes comparable with the effective Josephson penetration depth, we observed nearly homogeneous current distribution over the region common to the top and bottom junctions when the devices were biased across both the barriers in the absence of an external magnetic field. When the two junctions are biased separately, the current is concentrated at the junction edges in accordance with the behavior characteristic of distributed junctions. In an applied magnetic field, the vortex structure is confined to the area shared by both junctions when the device is biased as a whole. The experiment gives an indication that in the stationary state the spatial phase difference distribution of the two junctions coincides in the shared region at least in some interval of the external magnetic field. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363064

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have prepared by sputtering techniques a series of fcc [Fe1−xNix/Cu]×10 superlattices with sublayer thicknesses of 3 nm and with Ni concentrationsxranging from 0.26 to 0.54. The use of MgO single‐crystal substrates and Cu sublayers in the superlattice growth ensures a well‐defined fcc crystal structure in the Fe–Ni sublayers with a Ni concentration as low as 26 at. % and down to liquid helium temperatures. The magnetization of the Fe–Ni sublayers in the superlattices starts to deviate from the well‐known Slater–Pauling curve at 40 at. % Ni, and continues to drop until the fcc–bcc transition is completed. A strong dependence of the magnetization on temperature was also observed for the Fe–Ni sublayers in the Invar range, consistent with the behavior of bulk Fe–Ni Invar alloys. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363065

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have compared a single layer of La0.7Ba0.3MnO3and a trilayer structure of SrTiO3/La0.7Ba0.3MnO3/SrTiO3, both grown epitaxially on a LaAlO3substrate, using information obtained by ferromagnetic resonance (FMR). The trilayer samples have a more uniform magnetization and are not susceptible to environmental degradation. This may be due to the strain relief that the buffer SrTiO3layer provides for the La0.7Ba0.3MnO3layer. We have also studied the magnetic homogeneity of the trilayer structure as a function of the deposition temperature. The perpendicular FMR linewidth, &Ggr;⊥, shows a clear window in the deposition temperature where the linewidth is <50 Oe. However, the parallel linewidth, &Ggr;∥, is nearly ten times larger than &Ggr;⊥with only a weak dependence on the deposition temperature. This broadening of the parallel linewidth compared to the perpendicular linewidth can be explained by invoking a local unidirectional anisotropy in the plane of the film. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363066

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Calculations of exciton magnetic‐polaron (EMP) energies in semimagnetic quantum well structures and superlattices together with their temperature and magnetic field dependence have been performed. The influence on the EMP energies of the effects of enhanced paramagnetism at the interface and interface roughness are evaluated. It is shown that both these effects increase the theoretical EMP energy values and that interface disorder is the dominant factor in both cases. Furthermore, a more pronounced increase occurs for both effects in superlattices than in single quantum wells. Superlattices can also exhibit an additional type of disorder arising from variations in the barrier/well thickness. It is shown that this kind of disorder gives rise to an increase in the EMP energy values only when it leads to an overall narrowing of the well regions. A comparison with experimental values of the EMP energies in superlattices indicates the presence of small amounts of micro‐roughness in the reported structures on a scale that is similar to that required to account for magneto‐optical data. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363067

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The dielectric properties of (Ta2O5)1−x(SiO2)xpolycrystalline ceramics for 0.0≤x≤0.20 are reported. Measurements were made at 1 MHz and temperature between −40 and +100 °C. The dielectric properties are not very sensitive to SiO2content. A moderate enhancement of the dielectric constant is found, from −30 for pure Ta2O5to ∼45 atx&bartil;0.10. The temperature coefficient of dielectric constant in the vicinity of room temperature decreases from ∼200 ppm/°C for Ta2O5to ∼75 ppm/°C forx=0.14. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363068

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Polycrystalline Bi4Ti3O12thin films having layered perovskite structure were fabricated by metalorganic solution deposition technique on both Pt‐coated Si and bare Si substrates at a temperature as low as 500 °C. The effects of post‐deposition rapid thermal annealing on the structural and electrical properties were analyzed. The electrical measurements were conducted on metal–ferroelectric–metal capacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 184 and 0.018 and the remanent polarization and the coercive field were 4.4 &mgr;C/cm2and 84 kV/cm, respectively. The films exhibited high resistivity in the range 108–1012&OHgr; cm for films annealed at temperatures of 500–700 °C for 10 s. TheI–Vcharacteristics were found to be Ohmic at low fields and space‐charge‐limited at high fields. AV3/2dependence of the current was observed in the space‐charge region. This could be explained by assuming the mobility to be field dependent since in thin films the electric fields are invariably high even at low applied voltages. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363069

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Optical measurements of the individual ferroelectric/ferroelastic domain wall oscillations in the ac electric field were carried out up to the transition temperature. The amplitude of the wall vibrations fell abruptly to zero so that the wall was at rest during the phase transition. The change of oscillation characteristics with temperature is shown to be dependent on the history of motion, in part on the initial amplitude and the presence of the shell of mobile defects or charge carriers. Change of material parameters, influence of screening or defects shell, and critical damping are discussed as possible mechanisms of the effect. The last assumption is shown to be in a good agreement with the experimental data. The measurements of the amplitude of domain wall vibrations may be used as a simple method for investigations on critical phenomena in ferroelectrics. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363045

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

‘‘Sawtooth’’ superlattices of Zn(S,Se) were grown on GaAs substrates by a layer‐by‐layer atomic epitaxy growth technique. Larger scale variations in band gap were introduced by systematically varying the ratio of ZnS and ZnSe thickness over greater distance scales. These larger scale variation were themselves repeated in order to produce a superlattice in which the band gap had a sawtooth shaped profile. The structure and optical properties of these new materials were characterized by x‐ray diffraction and photoluminescence measurement. The x‐ray diffraction spectra showed satellite peaks corresponding to the large scale variations in structure. The strong blue photoluminescence peaks were observed and consistent with hole trapping in the sawtooth potential wells. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363070

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Lithiated Sn oxide films, denoted LixSnO2, were produced by reactive rf magnetron sputtering of Sn and electrochemical post‐treatment. Optical transmittance and Mo¨ssbauer spectra were recorded for progressively increased lithiation. Increasingxfrom zero to ∼0.1 did not have any significant effect on the optical data or Mo¨ssbauer spectra, and it is likely that the lithium is located in internal double layers in the film. Further increasingxfrom ∼0.1 to ∼0.2 yielded significant transmittance drops and Mo¨ssbauer spectra unambiguously showing a conversion Sn4+→Sn2+. Hence the optical absorption can be reconciled with intervalency transitions as in other cathodically coloring electrochromic oxides. Electrocrystallization appeared to dominate the electrochemistry atx≳0.2. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363071

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The room‐temperature infrared reflectance of AlN–GaN short period superlattice films has been measured. These superlattice films were deposited by switched atomic layer metalorganic chemical vapor deposition onto GaN or AlN buffer layers deposited on basal plane sapphire substrates. The measured reflectance spectra are compared to calculated spectra using an effective medium theory to model the dielectric function of the superlattice. The optical properties of the individual materials making up the samples are modeled with Lorentz oscillators using only bulk input parameters. The effects of film and substrate anisotropy and off‐normal incidence are included in the calculation. Using this modeling technique, it is possible to obtain thickness estimates for the superlattice film and the buffer layer. The complicated structures seen in the reststrahl region reflectance of these films are also analyzed by comparison to the calculated spectra. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.363072

出版商:AIP    

年代:1996

数据来源: AIP