摘要:

Fine powders of SnO and Fe2O3were thermally diffused into Y‐Ba‐Cu‐O systems composed of YBa2Cu3O7−&dgr;matrix with orientedcaxes and Y2BaCuO5precipitates. The magnetic hysteresis loops of the system were measured at 77 K as a function of an applied magnetic field direction defined as the angle between the field and thecaxis. The amplitude of the magnetization hysteresis &Dgr;M, which is proportional to the critical current densityJc, was increased by nonmagnetic impurities SnO. On the other hand, &Dgr;Mwas decreased drastically by magnetic impurities Fe2O3although the critical temperatureTcwas hardly decreased. In all the samples, the angular variation of &Dgr;Mshowed a maximum at &thgr;=0° and a minimum around &thgr;=90°. However a local maximum at &thgr;=90°, which is due to the intrinsic pinning, was observed only in the sample with diffused SnO. The intrinsic pinning of the sample with diffused Fe2O3was significantly suppressed and the two‐dimensional pinning property apparently became more pronounced. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358728

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Iron‐rich intermetallic compounds Sm2Fe17−xSixand Sm2Fe17−xSixC (x=0, 1, 2, and 3) were studied. The as‐prepared compounds are single phase with the rhombohedral Th2Zn17‐type structure except for Sm2Fe17C and Sm2Fe16SiC which contain some amounts of &agr;‐Fe. The unit cell volumes and saturation magnetization at room temperature are found to decrease linearly with increasing Si concentrationx. The Curie temperatureTcis found first to increase and then to decrease with increasing Si content. X‐ray diffraction measurements on magnetically aligned powder samples show that the easy magnetization direction of the Sm2Fe17−xSixsamples withx≤2 is planar while that of the sample withx=3 is conical. The Sm2Fe17−xSixC samples withx≤3 exhibit an easyc‐axis anisotropy at room temperature. The anisotropy field is 83 kOe forx=0 and it rises to 110 kOe atx=1, and then drops with increasing Si concentration to 55 kOe atx=3. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358729

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have produced Co1−xPtx(x=0.53 and 0.75) alloy films by dc magnetron sputtering at various substrate temperatures (RT‐300 °C) and sputtering pressures (2–10 mTorr). The magnetic properties of the films were examined by using vibrating sample magnetometry and Kerr hysteresis loop tracer. A (111) texture is observed in the as‐deposited film, and its degree is dependent on the substrate temperature and Ar pressure. The degree of the (111) texture does not affect the magnetic anisotropy. While the magnetic properties of the Co0.25Pt0.75alloy films are not sensitive to heat treatment, the coercivity and the loop squareness of the Co0.47Pt0.53alloy films are drastically increased by annealing. Structural analysis using transmission electron microscopy and x‐ray diffractometry reveals that CoPt(L10) and CoPt3(L12) ordered phases, respectively, are formed, each with a strong (111) texture. By comparing the magnetic properties between the CoPt(L10) and CoPt3(L12) ordered phases in relation to the atomic arrangements in a unit cell, it is concluded that the perpendicular magnetic anisotropy in the sputter‐deposited Co‐Pt alloy system depends mainly on the atomic arrangements of the Co and Pt. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358730

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The pressure dependence of the ‘‘hyperfine magnetic field’’‐Hhpfat the nuclei of the diamagnetic atoms119Sn was investigated in the Heusler alloy Co2MnSn using Mo¨ssbauer absorption spectroscopy with pressures up to 10 GPa at room temperature. The dependence can be fitted by the linear functionHhpfSn(P)/HhpfSn(0)=1+k1⋅Pwith coefficientk1=−0.023 ±0.002 GPa−1, whereHhpfSn(0)=10.5±0.3T. Diamond anvil cells were used for the high pressure generation. A drop ofHhpfSnin the pressure range 0–10 GPa can be explained on the basis of empirical theory developed by Delyagin, Krylov, and Nesterov [JETP76, 8, 1050 (1980)]. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359526

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The Maxwell–Wagner–Sillars (MWS) relaxation is studied for glass‐bead–polystyrene (PS) composites having compositions from 0% to ∼50% in volume, in the range 20 Hz–1 MHz and for temperatures varying from room temperature to 280 °C. For the PS matrix, the complex permittivities and ac conductivities are within the limits of 3.3–3.7 and 2–3×10−9&OHgr;−1 cm−1, respectively, at 1 kHz in a 120–180 °C temperature interval. For the glass, these parameters vary between 20 and 300 for the complex permittivity, and between 9×10−9and 4×10−8&OHgr;−1 cm−1for the ac conductivity, in the same conditions. Good agreement is found between the calculated values of the maximum loss factor frequencies and the experimental ones. The relaxation found in the composite at temperatures above the &agr; relaxation of the PS is ascribed to the trapping of conductive carriers at the interface between the glass spheres and the polymer matrix. This MWS relaxation is showed to have an activation energy of 20 kcal mol−1and a relaxation time of 10−13.6s. From the Argand representations it is observed that the MWS phenomenum deviates from a simple Debye‐like process for composites having glass volume fractions from 12.5% upward. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358731

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Inclined incidence of a shear horizontal elastic wave on a periodic structure of piezoelectric layers with metallized interfaces is considered. The layers are supposed to be made from the identical crystal of hexagonal symmetry but have alternating widthsd1,d2. Due to the condition of fixed electropotential, each interface provides the reflection proportional to the parameter of electromechanical couplingq2. The interference of the reflected waves in the periodic structure causes the existence of the Bragg resonances in the reflection‐transmission spectrum so that ‖R‖max≊1 for a sufficiently large number of layers. Sinceq2≪1, the considered reflection spectrum exhibits some specific features such as high selectivity, modulation of the heights of the Bragg maximums depending on the valued1/(d1+d2), and the extinction effect. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358732

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Barium‐strontium‐titanate (Ba0.5Sr0.5)TiO3thin film capacitors fabricated by a spin‐on technique were studied. At room temperature the films have high dielectric constant &egr;, ranging from 22 to 151 at 1 MHz. Complex impedance spectroscopy was used in order to measure the frequency dependence of their dielectric properties. Cole–Cole reactance versus resistance of experimental data in the frequency range 10 Hz–10 MHz show semicircular behavior indicative of current leakage. The current leakage is proportional to the dielectric constant and in particular the lowest leakage current we measured at 1 MHz was 3×10−5A/cm2on samples with &egr;=22. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358733

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Room‐temperature photoreflectance measurements of a GaAs/Al0.2Ga0.8As single‐quantum well structure showed well defined Franz–Keldysh oscillations in the neighborhood of the GaAs and Al0.2Ga0.8As band‐edge energies. That experiment investigated the origin of the Franz–Keldysh oscillations by sequential etching and photoreflectance analysis of the grown layers and showed that the phase of the Franz–Keldysh oscillations shifted as the upper Al0.2Ga0.8As barrier was etched, with eventual phase reversal when roughly half of the upper barrier was removed. Here, these phase shifts are determined accurately using a novel Kramers–Kronig approach and they are interpreted in terms of optical interference effects using both a simple two‐ray model and a multiple‐reflection treatment incorporating a calculation of the Seraphin coefficients. The results also enable the thickness of the layers removed to be determined. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358734

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Erbium photoluminescence at room temperature and at 77 K has been observed from porous silicon doped with erbium from a spin‐on silica gel film. Erbium incorporation into silicon dioxide at the surface of porous silicon and rapid thermal processing at temperatures higher than 1223 K were found to be a necessary prerequisite for erbium‐related luminescence in porous silicon. No erbium diffusion into monocrystalline silicon from the spin‐on films was observed. The depth‐dependent erbium concentration in the bulk of porous silicon was determined by secondary‐neutral‐ and secondary‐ion‐mass spectrometry depth profiling. The laterally resolved erbium distribution in the porous silicon was derived from energy‐dispersive x‐ray analysis. Possible mechanisms of erbium‐related luminescence in porous silicon are discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358735

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thermal donor formation in silicon at 390, 420, and 450 °C has been investigated and correlated with IR vibrational absorption bands observable at room temperature. It is suggested that oxygen is clustering in different structures giving rise to absorption bands at 975, 988, 1000, 1006, and 1012 cm−1. The bands at 975, 988, and 1000 cm−1are related to the three first appearing double donors as studied by low‐temperature infrared spectroscopy. The 1012 cm−1band is related to the most frequently appearing type of structure and is suggested to correspond to a different type of donor, possibly the shallow thermal donors or the new thermal donors. The development of the new bands with heat treatment time shows a complex behavior. The early stages of thermal donor formation as studied at 390 °C are not governed by ordinary long‐range oxygen diffusion but by a transformation process of pre‐existing clusters corresponding to the 1012 cm−1band. At 450 °C the cluster transformation process appears in parallel with an aggregation of oxygen atoms diffusing to the clusters. Another group of vibrational bands appears in the range 724–745 cm−1. These bands develop simultaneously with the 975–1012 bands and are suggested to be related to a different vibrational mode of the oxygen atoms in the clusters. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358736

出版商:AIP    

年代:1995

数据来源: AIP