摘要:

The techniques of ferromagnetic (FMR) and electron paramagnetic resonance have been applied in studies of a specimen of Pittsburgh No. 8 bituminous coal. The specimen has been found to be magnetically very heterogeneous, with paramagnetic Mn2+and Fe3+, free radicals, and at least one ferromagnetic specie which is identified and characterized in the present paper. The temperature dependence of the spectral line shapes indicates the occurrence of a phase transition at 123 K for a finely ground powder sample and at 121 K for a hand‐picked fragment; these temperatures are characteristic of the Verwey transition magnetite, and confirm its presence in both samples. Linewidth data provide an upper limit of 0.07 &mgr;m on the particle size in the powdered sample. The chemical composition of the magnetite in the powdered sample is estimated, on the basis of the observed transition temperature, to be between Fe2.988O4and Fe2.997O4. Spectra of the residue and the glass extract obtained after treatment of the powdered sample with HCl confirm the identification of magnetite, and indicate that it is not embedded in the organic matter in the coal, but should be easily removed either by acid treatment or magnetic separation. The results of this study suggest the potential usefulness of the FMR technique in the identification and physical and chemical characterization of ferro‐ and ferrimagnetic minerals in coals.

ISSN:0021-8979    

DOI:10.1063/1.334525

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Optical birefringence in liquid‐phase‐epitaxial‐grown (LPE) Bi‐substituted iron garnet films was investigated with annealing. The optical birefringence was found to be composed of a stress‐induced part and a growth‐induced part. The growth‐induced optical birefringence &Dgr;ngwas about 5×10−4at &lgr;=1.15 &mgr;m. &Dgr;ngand the growth‐induced magnetic anisotropyKgdisappeared after the annealing. Time constants for changes of &Dgr;ngandKgby the annealing were nearly the same and orders of a few hours at 1100–1150 °C. A deformation of the microscopic structure around bismuth ions seems to be responsible for both &Dgr;ngandKg. The large growth‐induced optical birefringence in Bi‐substituted iron garnet films plays an important role to achieve high efficiency TE‐TM mode conversion in magneto‐optical waveguides.

ISSN:0021-8979    

DOI:10.1063/1.334526

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The ferromagnetic resonance spectrum of a layered magnetic thin film is expected to show a number of standing spin‐wave resonances with a wavelength that matches the thickness of the film. For the case of perpendicular resonance such spectra were calculated for some typical films in which magnetic layers are alternated with weaker magnetic layers. Some useful approximations are discussed. The results of the calculations are compared with experimental perpendicular spectra measured on films in which fifty Permalloy layers alternate with Ni layers.

ISSN:0021-8979    

DOI:10.1063/1.334527

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The Mo¨ssbauer linewidth broadening of superparamagnetic particles of ferric hydroxysulfate, near the point where the paramagnetic lines begin to appear, has been investigated as a function of temperature. This behavior is explained by a geometric picture of an assembly of magnetically ordered single‐domain particles whose magnetic moments move within an asymmetric double‐well potential. A relaxation model is presented which combines the conventional theory of superparamagnetism with an exponential distribution of energy barriers.

ISSN:0021-8979    

DOI:10.1063/1.335471

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Simple mechanical models can be useful in investigating the structural dependence of the piezoelectric activity of uniaxially oriented polyvinylidene fluoride. An experimentally observed strong nonlinear relationship between the mechanical load and the transverse piezoelectric coefficientd32is presented. This new behavior is discussed on the basis of a parallel arrangement of crystalline and amorphous regions perpendicular to the orientation axis. The coefficientd32changes its sign also, the deformation being less than 3% in all cases. A mechanical series model is applied for the coefficientd31whose behavior is very linear with the applied mechanical load. Furthermore,d32shows a significant time dependence after a change in the mechanical load applied. These nonlinear effects depend upon structural features such as crystal perfection and were attributed to processes occurring in the crystalline regions and in their interfaces with the amorphous surrounding, respectively. Also, the technical importance of these effects is obvious.

ISSN:0021-8979    

DOI:10.1063/1.334528

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Time‐resolved site‐selection spectroscopy techniques using a pulsed tunable dye laser were used to investigate the spectral structure and dynamics of Eu3+ions in six oxide and one fluoride glass hosts. Network modifier ions were found to be important in determining the details of the spectral structure which can be related to the amount of local order in the glass. As the relative order increases, the fluorescence lifetime was found to decrease and the energy transfer rate increase. The transfer rate was found to vary linearly with the predicted ion‐ion interaction rate for the oxide glasses. Differences in the temperature and excitation wavelength dependences of the energy transfer rates were found for the different samples.

ISSN:0021-8979    

DOI:10.1063/1.334529

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new method is described for the calculation of the refractive index of semiconductors at energies below the lowest band gap, in which a model form of the imaginary part of the dielectric function is assigned and the refractive index is obtained, without introducing any empirical parameter. It provides good insight into the physics of the problem and a quantitative account of refractive index dispersion as well. Double‐beam reflectance measurements were made for the refractive index of four InP and GaAs samples. Results are presented for Si, Ge, AlAs, GaP, GaAs, and InP and show very good agreement with this model.

ISSN:0021-8979    

DOI:10.1063/1.334530

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Cathodoluminescence (CL) has been used to investigate the nature ofn‐type InP directly underneath AuGeNi ohmic contacts subjected to various heat treatments. The study of this contact system by CL has shown directly that the quality of the underlying InP is significantly modified up to distances of several microns from the contact interface. These changes are brought about by the interaction of the contact components with the semiconductor. Contrary to the widely accepted view, no evidence ofn+doping of the InP by Ge was observed in any of the contacts examined. Possible explanations for the observed reduction in CL efficiency obtained from the InP close to the contact interface are discussed.

ISSN:0021-8979    

DOI:10.1063/1.334531

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Optical coupling by absorption and reflection of a wafer during rapid thermal anneals (RTA) determines the temperature transients during heating, and the behavior of thermally activated processes. It is shown experimentally that the heating rate and temperatures during the early phases of a RTA cycle depend on the doping of the wafer being heated. High doping is accompanied by high free carrier absorption which results in a relatively rapid increase in temperature. Differences of heating rates of 50 °C/sec and temperatures several hundred degrees centigrade are obtained in the first 5 sec of a RTA cycle for N+and N−wafers and significant effects on the heating rate of heavily implanted wafers are also seen. Experiments were carried out using thermocouples, optical pyrometer and also by observing the lateral solid‐phase growth of silicon on sapphire (SOS). A simple theoretical description is given for the enhanced heating rate for N+and heavily implanted wafers.

ISSN:0021-8979    

DOI:10.1063/1.334532

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The doping of polycrystalline silicon films is known to structurally change the material, producing larger grains after annealing. The grain growth is especially enhanced during high‐temperature doping using a PBr3or POCl3dopant source. In this paper, we report our observation of the PBr3‐doping induced epitaxial growth in polycrystalline silicon films deposited on silicon substrates and on the silicon in windows etched in the oxide. Epitaxial films contained twins induced by the microcrystals at the substrate‐film interface. Models are proposed to explain possible mechanisms for grain growth of undoped and PBr3‐doped polysilicon films. Also proposed are possible explanations for the observed microcrystalline growth at the epitaxy‐substrate interface and in the epitaxial film itself.

ISSN:0021-8979    

DOI:10.1063/1.334533

出版商:AIP    

年代:1985

数据来源: AIP