摘要:

The induced in‐plane and local magnetic anisotropies of rf sputtered (Co93Zr7)100−xRExthin films were investigated as a function of RE content for RE=Pr, Nd, and Tb by transverse biased initial susceptibility measurements at both film/air and glass/film interfaces. The deposition was performed in a magnetic field. The films exhibit a very well defined in‐plane anisotropy with negligible long‐range fluctuations and a small coercive fieldHc, in accordance with the experimental data. The overall variations of the transverse susceptibility are related to the ripple. The variations of the local anisotropy with composition were measured. Both the induced anisotropyKuand the local anisotropyKlocincrease with the increasing amount of RE in the layers. A clear relationship betweenKuandKloccould be established. The results are discussed in terms of the single‐ion anisotropy of the rare earth. While the value ofKuis the same at both interfaces, the ripple constants were found to be slightly different. This last result is believed to be related to some local defects, the origin of which is also suggested. Also the coercive force is discussed and explained in terms of a theoretical model. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361259

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The magnetic hysteresis loops of mechanically stressed 15‐nm‐thick Ni film, measured by the magneto‐optical technique, were analyzed using the Stoner–Wohlfarth model. The influence of external stress on the shape of the hysteresis loop is accurately described by stress‐induced uniaxial anisotropy. The energy of the domain structure during magnetization reversal is equivalent to an additional uniaxial anisotropy. The processes of domain appearance and disappearance correspond to two different magnitudes of this anisotropy, while the moment of the change of anisotropy magnitude corresponds to the transformation of the Ne´el walls. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361260

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The aging characteristics of the electrostrictive lead magnesium niobate–lead titanate [(1−x)PMN–xPT] under dc bias field were investigated. It was observed that the amount of aging increases with the PT content for the compositions investigated (x≤0.3). For a fixed composition, the aging rate rises with temperature. It was shown that the aging follows a stretched exponential time law, which is typical for the time‐dependent behavior in polar glass and random field systems. In PMN–PT, the dielectric constant shows a much weaker aging than the piezoelectric coefficient, reflecting the importance of the stress coupling of the defect field to the micropolar region during the aging since the polar vector of the microregions can have both 180° and non‐180° reorientations while only the non‐180° reorientation contributes to the observed piezoelectric effect. Experimental results also reveal that the defect field developed during the aging in these materials under dc bias field is quite different from those in normal ferroelectrics and in Mn‐doped PMN and 0.9 PMN–0.1PT. The direction of the defect electric field is opposite to the direction of the original dc bias field, indicating that the defect field is the result of a direct coupling to the external bias field rather than induced by the polar domains. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361261

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

It was found that the spontaneous polarizationPsin some area of triglycine sulfate (DL‐alanine) crystal with periodic laminar ferroelectric domains cannot be reversed with an applied electric field. By using the nematic liquid‐crystal method, the direct observation of the dynamics of the domain walls in the switching processes has been carried out. It is reasonable to assume that above experimental phenomena are due to the existence of a series of inclined domain walls in the specimen. The experimental methods and some observed preliminary results are reported. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361262

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

GaAs/In0.07Al0.93As tensile‐strained quantum wells were grown on [001] GaAs substrates using molecular‐beam epitaxy. The incorporation of tensile strain is made possible by preparing a 1‐&mgr;m‐thick In0.07Al0.93As relaxed buffer which is followed by the growth of quantum wells. The strain of the GaAs was measured using Raman spectroscopy and photoluminescence. The photoluminescence measurements from wells ranging in thickness from 25 to 100 A˚ reveal that the observed optical transition originates from the electron–light hole recombination for a 100 A˚ well and from the electron–heavy hole recombination if the well thickness is less than 40 A˚. Therefore, a thick Al‐rich InxAl1−xAs relaxed buffer on the GaAs substrate can be used to engineer the relative energy position of the light and heavy holes for GaAs‐based quantum wells. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361263

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Epitaxial Ga2Se3layers were grown on GaP (100) and GaAs (100) by metal–organic chemical vapor deposition and the heterovalent exchange reaction, respectively. Measurements of the sample reflectance were carried out in the spectral range from 70 to 50 000 cm−1(∼10 meV−6.2 eV). The dielectric functions in the far infrared were determined from the reflectance measurements and are dominated by strong phonon features of the substrate and the layers. Substrate related multiphonon absorbances and Fabry–Perot interference dominate the mid infrared range. The spectra in the visible spectral range reveal Fabry–Perot interferences up to 2.6 eV indicating a fundamental band gap energy in the blue spectral range in contrast to the previously reported lower value of 2 eV. Further electronic transition energies were observed at 3.9, 4.7, and 5.0 eV. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361264

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Transmittance periodic oscillations are observed in GaSe and InSe on excitation with optical pulses. Such oscillations are explained in terms of photoacoustic generation of dilatational waves, which become resonant within the crystal. Spectral analysis of those oscillations in samples of different thickness has led to an accurate determination of the longitudinal acoustic‐wave velocity along the crystallographic axisc. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361219

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Differential reflectance modulation measurements in InGaAs/GaAs and GaAs/AlGaAs multiple quantum wells at room temperature are presented and discussed. In the energy range of the excitonic transitions the spectra obtained are strongly related to the first derivative of the reflectance curves. An exhaustive analysis of the line shape is carried out. It is shown how the modulation signal is related to the fluctuations of the alloy composition and of the well width. An estimate of the degree of inhomogeneity is obtained. The potential of the technique in spectral analysis and for homogeneity characterization is discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361265

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We use photoluminescence to study residual transition metal contaminants in GaN layers, which are grown by the sandwich technique either on 6H‐SiC substrate or on sapphire substrate. We observe three no‐phonon lines in the near infrared optical region at 1.3 eV, 1.19 eV, and 1.047 eV caused by 3d transition metals. The appearance of GaN related host modes in the phonon sideband of these emissions proves that the luminescence centers are incorporated in the hexagonal GaN layers. In this paper we especially focus on the luminescence band with the no‐phonon line at 1.047 eV. Temperature dependent photoluminescence measurements reveal an excited state splitting of 8 meV. In photoluminescence excitation spectroscopy we observe a further excited state at 1.6 eV with a fine structure splitting. The appearance of this excited state in the n‐type samples gives evidence that the defect must already exist in its luminescent charge state without illumination. The experimental results on the 1.047 eV emission fit to a4T2(F)→4A2(F) internal electronic transition of a transition metal with a 3d7electronic configuration. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361266

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Optical processes at the absorption edge in Y‐doped BaCeO3films with thicknesses of 160 and 4600 nm have been studied in the temperature region between 20 and 1000 °C. For the first time, optical band‐gap energies of Y‐doped BaCeO3were determined with a room temperature value of 4.1 eV and a temperature coefficient of −3.88×10−4eV/K. It was found that the optical absorption coefficient below the band–band transition exhibits an exponential dependence on photon energy following Urbach’s rule, and the Urbach tail is dependent on oxygen partial pressures, i.e., on lattice defects. The corresponding Urbach edge parameters and their temperature dependence were investigated. The data are discussed within the model of structural and thermal disorder and a characteristic phonon energy of 46 meV was obtained according to this disorder model. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361267

出版商:AIP    

年代:1996

数据来源: AIP