摘要:

We have studied the effect of tension and external field on the magnetization process in amorphous positive magnetostrictive Fe‐Si‐B wires. The radial stress created during the in‐rotating water quenching technique of producing these wires causes a radial anisotropy. Using a simple phenomenological model which assumes a continuous distribution for the values of these radial stresses, we fit the observed values of the remanence as a function of the applied longitudinal stress and obtain information about the stress distribution. We also explain in a consistent manner the dependence of the magnetization process on the applied longitudinal stress. On doing so, a value of the saturation magnetostriction constant &lgr;s=28×10−6is obtained for a Fe77.5Si7.5B15amorphous wire. In the stress dependence of the nucleation field for the Barkhausen jump we observe a minimum. A quantitative explanation for this minimum is given.

ISSN:0021-8979    

DOI:10.1063/1.346712

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper discusses the principles of magnetic force microscopy (MFM) and its application to magnetic recording studies. We use the ac detection method which senses the force gradient acting on a small magnetic tip due to fields emanating from the domain structure in the sample. Tip fabrication procedures are described for two types of magnetic tips: etched tungsten wires with a sputter‐deposited magnetic coating and etched nickel wires. The etched nickel wires are shown to have an apex radius on the order of 30 nm and a taper half‐angle of approximately 3°. Lorentz‐mode transmission electron microscopy of the nickel tips reveals that the final 20 &mgr;m is essentially single domain with magnetization approximately parallel with the tip axis. Images of written bit transitions are presented for several types of magnetic media, including CoPtCr, CoSm, and CoCr thin films, as well as &ggr;‐Fe2O3particulate media. In general, the written magnetization patterns are seen with high contrast and with resolution better than 100 nm. A number of magnetic recording applications are discussed, including the investigation of overwrite behavior and the writing characteristics in CoSm media at high data density. Computer calculations were performed to simulate the MFM response to written magnetic transitions. By including the extended geometry of the tip, the nonparallel orientation of the cantilever, and the finite width of the magnetic transitions, good agreement with experiment was obtained. The model calculations correctly predict the experimentally observed change in image contrast that occurs as a function of tip orientation. Computer calculations showing the dependence of resolution on tip geometry are also presented.

ISSN:0021-8979    

DOI:10.1063/1.346713

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Boron diffusivity in single‐crystal diamond has been investigated. To this aim, a novel method using impedance spectroscopy for the study of the atomic diffusivity in wide‐gap semiconductor has been developed, along with a model for the analysis of the dielectric response function. The advantages of this procedure are discussed. Boron diffusivity in diamond has been determined to be 6.9×10−20cm2 s−1at 800 °C. A discussion of the results and a comparison with previous estimates are presented.

ISSN:0021-8979    

DOI:10.1063/1.346714

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Infrared photoluminescence (PL) from InAsBi and InAsSbBi epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been studied. The PL from ternary InAsBi was investigated for Bi concentrations of ≤2.3 at. %. The peak energy decreases at a rate of 55 meV/at. % Bi with increasing Bi concentration. A study of the transmission spectra of these Bi‐containing alloys confirms the above result. The PL peak is assigned to near band edge emission for InAsBi. The value of dEg/dx=−55‐meV/at. % Bi is more than double the previously reported theoretical prediction for the band gap of InAsBi. The PL for the quaternary layer of InAsSbBi is also studied for Sb concentrations of <10 at. % and Bi concentrations of ≤1.5 at. %. Bi incorporation in InAs1−xSbx(0.07<x<0.10) reduces the PL peak energy at a rate of 46‐meV/at. % Bi. These results imply that incorporation of only a few percent of Bi is required in InAs0.35Sb0.65to achieve a band gap of 0.1 eV, equivalent to a wavelength of 12 &mgr;m, desired for infrared detector applications.

ISSN:0021-8979    

DOI:10.1063/1.346715

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present a calculation of the complex dielectric function, &egr;(&ohgr;)=&egr;1(&ohgr;)+i&egr;2(&ohgr;), at energies below and above the fundamental absorption edge of the hexagonal, wurtzite‐type semiconductor CdSe. This model includes theE0,E1, andEidg(indirect) gaps as the main dispersion mechanisms. The model is made to properly account for the excitonic effects at these critical points. Results are in satisfactory agreement with recent ellipsometric measurements over the entire range of photon energies (E=0–5.0 eV). Detailed discussions are presented on the results, with emphasis on the information about the electronic energy‐band structures and their group‐symmetrical selection rules of this material.

ISSN:0021-8979    

DOI:10.1063/1.346716

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Room‐temperature optical absorption over a large dynamic range is reported for single‐ crystal undoped yttrium aluminum garnet (Y3Al5O12or YAG). Absorption results are presented for the energy ranges 1.8 to 3.0 and 4.5 to 6.5 eV. For this work, ultraviolet (UV) absorption measurements were performed on four different boules of Czochralski‐grown undoped YAG. Absorption features were observed at 4.8 and 5.6 eV which can be attributed, at least in part, to trace impurity concentrations. Along with the UV measurements, calorimetric absorption results are presented at several laser wavelengths in the visible and near infrared (IR). The calorimetric results suggest a value of 1.5×10−3cm−1for the absorption coefficient of undoped YAG in the red and near IR. From the combination of UV and calorimetric measurements, an empirical estimate of the absorption coefficient from the visible to the UV is presented for undoped YAG. In addition to the absorption spectra, detailed chemical analyses and sample histories are given for the as‐grown optical quality YAG utilized herein.

ISSN:0021-8979    

DOI:10.1063/1.346717

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The reduction of pentavalent vanadium ions in aqueous solutions upon laser irradiation has been confirmed by using optical absorption and fluorescence techniques. X‐ray photoelectron spectroscopy (XPS) study revealed that V2O5was reduced to lower oxides upon laser treatment. Furthermore, the presence of reduced valence states of vanadium has been detected through XPS in vanadium‐containing solids such as V2O5/P2O5glass, thin films prepared separately from V2O5powder and the glass.

ISSN:0021-8979    

DOI:10.1063/1.346718

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Optical absorption measurements of the 2.0‐eV band and photoluminescence measurements of the 1.9‐eV emission, excited by various excitation bands, were carried out on high‐purity silica glasses subjected to &ggr;‐ray irradiation. Two, and possibly three, different forms of nonbridging oxygen hole centers were deconvoluted from the results of the isochronal annealing experiments. The difference in the peak wavelength of the 2.0‐eV absorption and 1.9‐eV luminescence bands among various forms of nonbridging oxygen hole centers is reported.

ISSN:0021-8979    

DOI:10.1063/1.346719

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Quantum‐confinement‐induced shifts in the fundamental absorption edge of isolated CdTe crystallites are reported in CdTe‐glass composite thin films produced using a sequential rf magnetron sputtering process employing two separate sputtering sources. Films ranging in thickness from 0.5 to 4.5 &mgr;m and containing as much as 30 vol % CdTe have been produced, illustrating the versatility of this technique over a more conventional melting approach. Post‐deposition heat treatments were used to produce average crystallite sizes in the range 46–158 A˚. An improved fit to theory at larger crystal sizes is found if a cylindrical crystal morphology is assumed. The effective mass of the confined specie, which governs the shift of the absorption edge with crystal size, is found to be 0.20m0(spherical morphology) and 0.12m0(cylindrical morphology), both of which are greater than the exciton‐reduced mass in bulk CdTe. The data suggests, therefore, that a non‐negligible Coulomb interaction may still exist in crystals even as small as 0.31 times the size of the bulk Wannier exciton diameter. Planar waveguiding has also been demonstrated in these samples as a preliminary step to the production of waveguide‐based nonlinear device structures.

ISSN:0021-8979    

DOI:10.1063/1.346720

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

External bremsstrahlung spectra produced by the complete absorption of beta particles from the decay of32P in compounds, some of them used as nuclear radiation detectors including CdO, NaI, CsI, BiI3, HgI2, PbI2, and HgO, and in thick targets of Ni, Cu, Mo, Cd, Ta, and Pb, are measured using a NaI(T1) detector. The bremsstrahlung energy yields are calculated using the unfolded bremsstrahlung spectra. The effective atomic numbers of compounds for the bremsstrahlung process are interpolated from the energy yield data of elements and compounds. Although the experimental effective atomic numbers of compounds are consistently lower than the theoretical ones, the overall agreement between the experimental values and those derived from the Markwich and Van Greiken expression for the modified effective atomic number [A. A. Markowicz and R. E. Van Grieken, Anal. Chem.56, 2049 (1984)] and from the expression for the mean atomic number, which has commonly been used for samples composed of more than one element, is good within experimental uncertainties. However, the experimentally derived effective atomic numbers are closer to the modified atomic numbers than to the mean atomic numbers. The linear relationship between the total energy yield and the atomic numberZdoes not strictly hold, and hence the equation of Kramers for total bremsstrahlung intensity is approximately valid. The exponent of the atomic number in the Kramers equation is found to be 1.08. The Kramers law is modified to give a better description of the experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.346721

出版商:AIP    

年代:1990

数据来源: AIP