Showing papers in "Journal of Applied Physics in 1988"
TL;DR: In this paper, the magnetic properties of Fe•Si•B•M alloys prepared by annealing amorphous alloys made by the single roller method over their crystallization temperature have been investigated for development of new Fe•based soft magnetic alloys.
Abstract: The magnetic properties of Fe‐Si‐B‐M (M: additives) alloys prepared by annealing amorphous alloys made by the single roller method over their crystallization temperature have been investigated for development of new Fe‐based soft magnetic alloys. Excellent soft magnetic properties were obtained by adding the two elements Cu and Nb to Fe‐Si‐B alloys. It was found that these new alloys, called ‘‘FINEMET,’’ have an ultrafine grain structure composed of bcc Fe solid solution. They are suitable for many kinds of magnetic components such as saturable reactors, choke coils, and transformers, because they have superior soft magnetic properties and a high saturation flux density, and because different types of B‐H hysteresis loops are obtained by magnetic field annealing.
2,938 citations
TL;DR: In this paper, the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI (e.g., Cd1−mnxSe, Hg 1−mnsTe) were reviewed.
Abstract: We review the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI (e.g., Cd1−xMnxSe, Hg1−xMnxTe). Crystallographic properties are discussed first, with emphasis on the common structural features which these materials have as a result of tetrahedral bonding. We then describe the band structure of the AII1−xMnxBVI alloys in the absence of an external magnetic field, stressing the close relationship of the sp electron bands in these materials to the band structure of the nonmagnetic AIIBVI ‘‘parent’’ semiconductors. In addition, the characteristics of the narrow (nearly localized) band arising from the half‐filled Mn 3d5 shells are described, along with their profound effect on the optical properties of DMS. We then describe our present understanding of the magnetic properties of the AII1−xMnxBVI alloys. In particular, we discuss the mechanism of the Mn++‐Mn++ exchange, which underlies the magnetism of these materials; we present an analytic formulation for the magnetic susc...
2,895 citations
TL;DR: In this paper, a brief review of the history of ac ionic and electronic conduction in disordered solids is given, followed by a detailed discussion of the simplest possible realistic model: the random free energy barrier model.
Abstract: A brief review of the history of ac ionic and electronic conduction in disordered solids is given, followed by a detailed discussion of the simplest possible realistic model: the random free‐energy barrier model. This model assumes conduction takes place by hopping, where the hopping charge carriers are subject to spatially randomly varying energy barriers. The model is solved in the continuous time random walk and in the effective medium approximation, and it is shown that the two solutions are almost indistinguishable. In the random free‐energy barrier model, the frequency‐dependent conductivity is completely determined by the dc conductivity and the dielectric loss strength. The model correctly predicts all qualitative features of ac conduction in disordered solids, and a comparison to experiment on a large number of solids shows that the model is also quantitatively satisfactory.
832 citations
TL;DR: In this paper, the surface energy of a silicon-on-insulator was evaluated based on crack propagation theory, and it was found that the bond strength increased with the bonding temperature from about 60-85 erg/cm2 at room temperature to ≂2200 erg/ cm2 at 1400°C.
Abstract: Several aspects of a new silicon‐on‐insulator technique utilizing bonding of oxidized silicon wafers were investigated. The bonding was achieved by heating in an inert atmosphere a pair of wafers with hydrophilic surfaces contacted face‐to‐face. A quantitative method for the evaluation of the surface energy of the bond based on crack propagation theory was developed. The bond strength was found to increase with the bonding temperature from about 60–85 erg/cm2 at room temperature to ≂2200 erg/cm2 at 1400 °C. The strength was essentially independent of the bond time. Bonds created during 10‐s annealing at 800 °C were mechanically strong enough to withstand the mechanical and/or chemical thinning of the top wafer to the desired thickness and subsequent device processing. A model was proposed to explain three distinct phases of bonding in the temperature domain. Electrical properties of the bond were tested using metal‐oxide‐semiconductor (MOS) capacitors. The results were consistent with a negative charge de...
819 citations
TL;DR: In this article, a crack-free transparent ferroelectric polycrystalline Pb(Zr,Ti)O3 thin films were prepared by spin-coating solutions of complex alkoxides.
Abstract: Crack‐free transparent ferroelectric polycrystalline Pb(Zr,Ti)O3 thin films were prepared by spin‐coating solutions of complex alkoxides. The preparation of stock solution, firing, and annealing of films was described. The coating of the intermediate layer of Al2O3 increased the adhesion between Pb(Zr,Ti)O3 thin films and glass substrates. The crystalline phases of films with varying Zr/Ti ratios were investigated. The dielectric constants were about 260. The remanent polarization and coercive field were 6.6 μC/cm2 and 26.7 kV/cm, respectively. The refractive index of the perovskite Pb(Zr,Ti)O3 films was 2.6 at 6328 A, and the absorption edge was at 3400 A. The quadratic and linear electro‐optic effects were measured with respect to the Zr/Ti ratio from 40/60 to 60/40 for films grown on glass substrates. The quadratic and linear electro‐optic coefficients were about 1×10−18 m2 /V2 and 2.4×10−11 m/V at 6328 A, respectively.
608 citations
TL;DR: In this paper, the authors describe magnetization, resistivity, and x-ray diffraction data that consistently support sharper interfaces in Pd/Co thin-film layered structures (LS) than in Pt/Co LS.
Abstract: rf sputtered Pd/Co and Pt/Co thin‐film layered structures (LS) have perpendicular magnetic anisotropy, when the Co layer is ultrathin (<8 A in Pd/Co and <14 A in Pt/Co). The Co thickness (T) dependence of the anisotropy energy (Ku∼T) and the effective anisotropy field (HK∼1/T) in Pd/Co LS support an interfacial anisotropy as the source of the perpendicular magnetic easy axis. In contrast, the anisotropy is independent of Co thickness for thin Co layers in Pt/Co LS, and thus the mechanism for the perpendicular easy axis is thought to be different. We describe magnetization, resistivity, and x‐ray diffraction data that consistently support sharper interfaces in Pd/Co LS than in Pt/Co LS.
599 citations
TL;DR: In this article, a large variety of experimental data on IILD are discussed and provide newer information and further perspective on crystal self-diffusion, impurity diffusion, and also the important defect mechanisms that control diffusion in AlxGa1−xAs-GaAs, and in related III-V semiconductors.
Abstract: The process of impurity‐induced layer disordering (IILD) or layer intermixing, in AlxGa1−xAs‐GaAs quantum well heterostructures (QWHs) and superlattices (SLs), and in related III‐V quantum well heterostructures, has developed extensively and is reviewed. A large variety of experimental data on IILD are discussed and provide newer information and further perspective on crystal self‐diffusion, impurity diffusion, and also the important defect mechanisms that control diffusion in AlxGa1−xAs‐GaAs, and in related III‐V semiconductors. Based on the behavior of Column III vacancies and Column III interstitials, models for the crystal self‐diffusion and impurity diffusion that describe IILD are reviewed and discussed. Because impurity‐induced layer disordering has proved to be an important method for III‐V quantum well heterostructure device fabrication, we also review the application of IILD to several different laser diode structures, as well as to passive waveguides. We mention that it may be possible to reali...
481 citations
TL;DR: In this paper, the clean surface of a silicon single crystal was prepared with ultraviolet cleaning followed by HF dipping with low concentration HF obtained by dilution by organic free ultrapure water, at room temperature under the atmospheric condition.
Abstract: We have tried to develop a new procedure to prepare the clean surface of a silicon single crystal. We successfully prepared the contamination free bare silicon surface with ultraviolet cleaning followed by HF dipping with low concentration HF obtained by dilution by organic free ultrapure water, at room temperature under the atmospheric condition. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet photoelectron spectroscopy measurements proved thus prepared surface has a hydrogen monoatomic layer terminating the dangling bonds of silicon. The hydrogen termination was found to have remarkable passivation effect against surface oxidation reaction. A silicon thin‐film epitaxially grown on the prepared surface was confirmed to have perfect crystal structure and high‐purity level by scanning electron microscopy, reflection high‐energy electron diffraction, Raman spectroscopy and secondary ion mass spectroscopy.
451 citations
TL;DR: In this article, an effective mass model for n-doped semiconductors is proposed for n−doped polysilicon, where the Al atoms act as pointlike Coulomb scatterers and are screened by the electrons acco...
Abstract: ZnO:Al coatings were prepared by rf magnetron sputtering of ZnO together with dc magnetron sputtering of Al onto rapidly revolving unheated substrates under weakly oxidizing conditions. Optimized films had ∼1% luminous absorptance, ∼85% thermal infrared reflectance, and ∼5×10−4 Ω cm electrical resistivity at a thickness of ∼0.3 μm. The Al content was ≲2 at. %, as determined by Rutherford backscattering spectrometry. Transmission electron microscopy and electron diffraction showed ∼50‐nm average crystallite size and a hexagonal wurtzite structure. Spectrophotometric transmittance and reflectance were recorded in the 0.2–50‐μm wavelength interval, and the complex dielectric function was evaluated by computation. The optical data were explained from an effective mass model for n‐doped semiconductors. The Al atoms are singly ionized, and the associated electrons occupy the bottom of the conduction band as free‐electron gas. The Al ions act as pointlike Coulomb scatterers and are screened by the electrons acco...
437 citations
TL;DR: In this article, a model for the plasma enhanced chemical vapor deposition of amorphous hydrogenated silicon (a•Si:H) in rf and dc discharges is presented.
Abstract: A model for the plasma enhanced chemical vapor deposition of amorphous hydrogenated silicon (a‐Si:H) in rf and dc discharges is presented. The model deals primarily with the plasma chemistry of discharges sustained in gas mixtures containing silane (SiH4). The plasma chemistry model uses as input the electron impact rate coefficients generated in a separate simulation for the electron kinetics and therefore makes no a priori assumptions as to the manner of power deposition. Radical densities and contributions to film growth are discussed as a function of gas mixture, electrode separation, and locale of power deposition, and comparisons are made to experiment. A compendium of reactions and rate constants for silane neutral and ion chemistry is also presented.
431 citations
TL;DR: A method of localized stimulation of the human brain by a pair of coils positioned outside the head so that time‐varying magnetic fields pass through the head in the opposite directions around a target results in an increased current flow at the target.
Abstract: A method of localized stimulation of the human brain is proposed. The basic idea is to concentrate induced eddy currents locally in the vicinity of a target in the cortex by a pair of coils which are positioned outside the head so that time‐varying magnetic fields pass through the head in the opposite directions around a target. The eddy currents induced at the target are expected to flow together, which results in an increased current flow at the target. Spatial distributions of induced eddy currents are calculated in cubical and spherical volume conductor models by a finite element method. The results show that the current vectors make themselves two vortexes which flow together at the target. The current density at the target makes a peak which is higher by 2–3 times than current densities at nontarget regions. The validity of the proposed method is demonstrated by experiments using frog nerve‐muscle preparations.
TL;DR: In this article, the authors measured coercive field and switching voltage versus thickness in PbZr0.54Ti0.46O3 thin (0.15-0.50 μm) films, together with switching times and current transient shapes versus field and temperature.
Abstract: We have measured coercive field and switching voltage versus thickness in PbZr0.54Ti0.46O3 thin (0.15–0.50 μm) films, together with switching times and current transient shapes versus field and temperature. The results show activation fields of order 120 kV/cm at room temperature, threshold voltages below 1.3 V, and switching speeds faster than 100 ns, demonstrating that fast, nonvolatile memories can be constructed that are compatible with standard silicon or GaAs integrated circuit voltage levels, without the need for an internal voltage pump. The displacement current transient data yield 2.5 as the dimensionality of domain growth if one‐step intial nucleation rate is assumed, and are compatible with the theory of Ishibashi, yielding imaxtmax/Ps=1.65±0.23, in comparison with the predicted 1.646. The switching time exhibits an activation field dependence upon both voltage and temperature through a single reduced parameter (TC−T)(VTC),−1 in accord with the theory of Orihara and Ishibashi.
TL;DR: In this article, the magnetic anisotropy of Co ultrathin films sandwiched by Au was investigated and it was shown that the easy magnetization direction becomes perpendicular to the film plane for Co thicknesses lower than 11 A.
Abstract: We present experimental and theoretical investigations on the magnetic anisotropy of Co ultrathin films sandwiched by Au. Ferromagnetic resonance experiments revealed the presence of a large perpendicular surface anisotropy that makes the easy magnetization direction become perpendicular to the film plane for Co thicknesses lower than 11 A, as is observed in magnetization measurements. In order to explain this surface anisotropy, we propose various models, taking into account the imperfections of the films. For thicknesses below 11 A, there is a large increase of the coercive field with decreasing thickness. This effect is tentatively interpreted in a model of propagating Bloch walls, where the interfacial roughness plays an important role.
TL;DR: In this paper, the authors present a laser-target scaling model which permits approximate prediction of the dependence of ablation pressure, mechanical coupling coefficient, and related parameters in vacuum upon single-pulse laser intensity (I), wavelength (λ), and pulse width (τ).
Abstract: We present a laser‐target scaling model which permits approximate prediction of the dependence of ablation pressure, mechanical coupling coefficient, and related parameters in vacuum upon single‐pulse laser intensity (I), wavelength (λ), and pulse width (τ) over extremely broad ranges. We show that existing data for vacuum mechanical coupling coefficient for metallic and endothermic nonmetallic, surface‐absorbing planar targets follows this empirical trend to within a factor of 2 over 7 orders of magnitude in the product (Iλ(τ)1/2). The comparison we present is valid for intensity equal to or greater than the peak‐coupling intensity Imax, where denseplasma formation mediates laser‐target coupling. Mechanical coupling coefficients studied ranged over two orders of magnitude. The data supporting this trend represent intensities from 3 MW/cm2 to 70 TW/cm2, pulse widths from 1.5 ms to 500 ps, wavelengths from 10.6 μm to 248 nm, and pulse energies from 100 mJ to 10 kJ. With few exceptions, data approximating one‐dimensional or planar expansions were selected. Previously, meaningful scaling of ablation pressure parameters with I, λ, τ was not possible because existing data concentrated in a small range of these parameters. Our own data, obtained in the low‐ and midrange of (Iλ(τ)1/2), completes the experimental picture. Since this new data was derived from five separate experiments with specialized character and purpose, detailed accounts of this work will appear separately. In this paper, we summarize the experimental conditions and selectonly those data which are relevant to the scaling issue. We find that laboratory‐scale laser experiments can often give impulse coupling data which agree with results from much higher‐energy experiments without much error, and at much lower cost. We review a theory of vacuum laser ablation, specialize it to a quantitative description of mechanical coupling, and show that the resulting model provides a simple physical description which comes quite close to the observed empirical trend. This is accomplished with minor elaborations of the theory as originally presented to account for the temperature dependence of plasma ionization states, while adhering to the premise that a simple and generally applicable treatment of laser impulse production should be available. The theoretical model can quantitatively predict vacuum ablation pressure foropaque targets without adjustable parameters to the factor‐of‐2 accuracy in which we are interested. Other published scaling models omit one or more of the important variables, lack broad applicability, or deviate more noticeably from the observed trend.
TL;DR: In this paper, a new theory involving a random field at the interface which causes the antiferromagnet to break up into domains, whose size is inversely proportional to the exchange field offset is described.
Abstract: Exchange anisotropy refers to a group of phenomena which appear in ferromagnetic‐antiferromagnetic sandwiches, particularly to a field offset in the hysteresis loop. After a brief review of experiment and earlier theory, a new theory is described involving a random field at the interface which causes the antiferromagnet to break up into domains, whose size is inversely proportional to the exchange field offset. The theory is extended by considering the temperature dependence and also the topological properties of the domains, in particular nonzero winding numbers which increase the size of the domains and give them added stability. The metastability of such structures provides an explanation of the magnetic ‘‘training’’ effect observed in multiple cycles of the hysteresis loop.
TL;DR: In this article, a computer simulation model was developed to conduct micromagnetic studies of thin magnetic films, where each grain is a single domain particle whose magnetization reverses by coherent rotation.
Abstract: A computer simulation model has been developed to conduct micromagnetic studies of thin magnetic films. Thin‐film media are modeled as a planar hexagonal array of hexagonally shaped grains. Each grain is a single domain particle whose magnetization reverses by coherent rotation. The computation utilizes coupled gyromagnetic dynamic equations with phenomenological Landau–Lifshitz damping. In particular, the effects of particle interactions are investigated. The effect of media microstructure on magnetic hysteresis is examined as well as the effect of intergranular exchange coupling. The difference between planar and completely random orientation of the crystalline anisotropy axes is discussed. Recorded transitions are simulated by allowing a pair of perfect transitions to relax. With no intergranular exchange coupling, the transitions show profound irregularity and zig‐zag structure. Intergranular exchange coupling produces more uniform transitions with increased zig‐zag structure amplitude. For a closely ...
TL;DR: In this paper, the average grain size of the crystallized amorphous silicon films depends on the annealing temperature and the deposition conditions, and the final grain size is also influenced by the annaling temperature with the largest grain size obtained at low-annealing temperatures.
Abstract: The crystallization of undoped amorphous silicon films deposited by low‐pressure chemical vapor deposition in the temperature range 580–530 °C and annealed from 550 to 950 °C has been studied by transmission electron microscopy. The average grain size of the crystallized films depends on the annealing temperature and the deposition conditions. The nucleation rate of new grains during annealing decreases as the deposition temperature decreases from 580 to 545 °C and/or when the deposition rate increases. The final grain size is also influenced by the annealing temperature with the largest grain size obtained at low annealing temperatures. A simple model is described which explains the dependence of grain size on the annealing temperature. An average grain size of 500 nm has been obtained in a 200‐nm film deposited at 545 °C and annealed at 550 °C.
TL;DR: In this article, a cubic discretization procedure of the micromagnetic energy functional is used to carry out numerical studies of the magnetization process in ferromagnetic cubes and their switching behavior is calculated for particle sizes in the range from 100 to 550 A.
Abstract: A cubic discretization procedure of the micromagnetic energy functional is used to carry out numerical studies of the magnetization process in ferromagnetic cubes. Equilibrium magnetization configurations and their switching behavior are calculated for particle sizes in the range from 100 to 550 A. In the model calculations the particles are assumed to have uniaxial crystalline anisotropy with an anisotropy constant of 18 500 erg/cm3, a saturation magnetization of 370 emu/cm3, and an exchange constant of 10−6 erg/cm. For particle sizes smaller than 520 A the remanent state has a flowerlike magnetization configuration. Beyond 520 A this state is replaced by a vortex structure about the easy axis. For particles smaller than 450 A switching occurs by approximately uniform rotation of the flower state. The switching fields are larger than the corresponding Stoner–Wohlfarth value. Beyond 450 A the application of an external field leads to the formation of a vortex configuration. The switching of the vortex con...
TL;DR: In this article, the authors describe information which has been obtained on point defects detected in various types of GaAs materials using electron paramagnetic resonance as well as electrical and optical techniques, concluding that native defects are not simple intrinsic defects, with the exception of the antisites, but complexes formed by the interaction of such defects between themselves or with impurities.
Abstract: We describe information which has been obtained on point defects detected in various types of GaAs materials using electron paramagnetic resonance as well as electrical and optical techniques. From a comparison of their characteristics and those of simple intrinsic defects (As and Ga interstitials, vacancies and antisites) it is concluded that native defects are not simple intrinsic defects, with the exception of the antisites, but complexes formed by the interaction of such defects between themselves or with impurities. Particular emphasis is given to the As antisite complexed with an As interstitial, the so‐called EL2 defect which plays a major role in the electrical properties of bulk materials. Differential thermal analysis, positron annihilation, and x‐ray diffraction demonstrate that bulk materials contain a large concentration of vacancy‐related defects and As precipitates located along dislocations which play the role of gettering centers. Presumably, bulk materials also contain other As clusters of various sizes although only the smallest ones (EL2) have been detected. All these As clusters are sources of As interstitials which play an important role in thermal treatments. As to semi‐insulating materials, their electrical properties result mainly from the compensation between the double donor, called EL2, associated with the As antisite and the double acceptor ascribed to the Ga antisite.
TL;DR: Theoretical expressions for the internal and external electromagnetic fields for an arbitrary electromagnetic beam incident upon a homogeneous spherical particle are derived, and numerical calculations based upon this theoretical development are presented in this paper.
Abstract: Theoretical expressions for the internal and external electromagnetic fields for an arbitrary electromagnetic beam incident upon a homogeneous spherical particle are derived, and numerical calculations based upon this theoretical development are presented. In particular, spatial distributions of the internal and near‐surface electric field magnitude (source function) for a focused fundamental (TEM00 mode) Gaussian beam of 1.06 μm wavelength and 4 μm beam waist diameter incident upon a 5‐μm‐diam water droplet in air are presented as a function of the location of the beam focal point relative to the sphere center. The calculations indicate that the internal and near‐surface electric field magnitude distribution can be strongly dependent upon relative focal point positioning and may differ significantly from the corresponding electric field magnitude distribution expected from plane‐wave irradiation.
TL;DR: The physics and technology of a relatively new, short-time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper.
Abstract: The physics and technology of a relatively new, short‐time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper. Low‐cost, minimum overall thermal budget, low‐power consumption, and high throughput are some of the attractive features of RIP. The discussion of RIP, in the context of other thermal processes, history, operating principles, different types of RIP systems, various applications of RIP using single processing steps, and novel applications of RIP, including in situ processing and multistep processing, is described in detail. Current trends are in the direction of RIP‐dominated silicon integrated circuit fabrication technology that can lead to the development of the most advanced three‐dimensional integrated circuits suitable for applications such as parallel processing and radiation hardening. RIP is not only a superior alternative to furnace processing, but it is also the only way to perform certain crucial steps in the processing of compound semiconductor devices such as high‐mobility transistors, resonant tunneling devices, and high‐efficiency solar cells. Development of more accurate temperature measurement techniques and theoretical studies of heat transfer and other fundamental processes are needed. Dedicated equipment designed for a specific task coupled with in situ processing capabilities will dominate the future direction of RIP.
TL;DR: In this article, a secondary ion mass spectrometry technique for compositional analysis of matrix elements is described, which consists of detecting the molecular ions CsM+ rather than M± ions under Cs+ primary ion bombardment.
Abstract: We describe a new secondary ion mass spectrometry technique for compositional analysis of matrix elements. It consists of detecting the molecular ions CsM+ rather than M± ions (M is the matrix element to be analyzed) under Cs+ primary ion bombardment. The linear behavior of the CsM+ ion yield makes the analysis independent of the matrix effect. An application to in‐depth quantitative compositional analysis for AlGaAs/GaAs multilayer structures is given. The compositions were determined with an absolute accuracy better than 2% and the depth resolution was smaller than 100 A.
TL;DR: The kinetics and chemistry of SiSiO2 interface trap annealing were examined in detail in this paper, with several process variables as parameters: oxide thickness, anneal ambient, temperature, bulk carrier type, metallization damage, and orientation.
Abstract: The kinetics and chemistry of Si‐SiO2 interface trap annealing are examined in detail Measurements of interface trap density Dit as a function of anneal time were performed with several process variables as parameters: oxide thickness, anneal ambient, temperature, bulk carrier type, metallization damage, and orientation Experiments were carried out using rapid thermal processing and capacitance‐voltage measurements of aluminum gate metal‐oxide‐semiconductor capacitors Anneal temperature and crystal orientation have the strongest effect on the kinetics 〈100〉 interfaces can be described by a power‐law temporal variation; 〈111〉 kinetics are slightly more complicated In both cases the experimentally observed anneal behavior is in conflict with the commonly used second‐order surface recombination model We propose a two‐reaction model involving atomic hydrogen dimerization and hydrogen/interface trap reactions This model sucessfully predicts anneal kinetics over a temperature range of 170–500 °C, representing a 106 dynamic range in anneal rates The difference in anneal behavior between 〈111〉 and 〈100〉 interfaces is explained by postulating different trap anneal mechanisms for the Pb0 and Pb1 defect centers This hypothesis is supported by trap production kinetics induced by extended anneals
TL;DR: In this article, the relative intensity of a 1400 cm−1 band against a 1530 cm− 1 band was found to decrease with an increase of sp3 content in amorphous carbon (a•C) films.
Abstract: Raman spectra of diamondlike amorphous carbon (a‐C) films prepared under atmosphere with various hydrogen gas content have been measured as a function of excitation wavelength. The Raman spectral profiles vary with excitation wavelength depending on electronic absorption spectra associated with π‐π* electronic transitions. Dependence of Raman spectra on excitation wavelength is interpreted in terms of π‐π* resonant Raman scattering from aromatic rings with various sizes rather than polyene chains. The relative intensity of a 1400 cm−1 band against a 1530 cm−1 band is found to decrease with an increase of sp3 content in a‐C films. It is shown that the relative intensity can be used as a parameter for sp3 content.
TL;DR: In this article, the effect of milling intensity on the glass formation has been studied for the first time, showing that deep eutectics do not play any role, contrary to amorphization by melt spinning.
Abstract: Amorphous Ni‐Zr powders have been prepared by mechanical alloying from crystalline elemental powders. The glass‐forming range has been determined by x‐ray diffraction, differential scanning calorimetry and saturation magnetization measurements. From 27 to 83 at. % Ni the powders become amorphous. This shows that deep eutectics do not play any role, contrary to amorphization by melt spinning. Crystallization temperatures, crystallization enthalpies, and wave numbers Qp, obtained from x‐ray diffraction investigations, are compared with the data received for rapidly quenched samples. In addition, the effect of the milling intensity on the glass formation has been studied for the first time. If the intensity is too high, crystalline intermetallic phases are formed. On the other hand, the powder needs an extended milling time to become completely amorphous if the milling intensity is too low. Conclusions on the actual temperature of the individual particle during mechanical alloying and on the glass‐forming process are drawn from these results.
TL;DR: In this article, the magnetic and invar properties of RFe10T2 compounds have been studied and an analysis of the magnetocrystalline anisotropy in these materials is given.
Abstract: The structures and the magnetic properties of some novel ternary compounds were studied. These compounds have the approximate composition RFe10T2, where T represents Cr, V, Ti, Mo, W, or Si. The structure of all these compounds can be derived from the tetragonal ThMn12 structure type, but the crystallographic position occupied by the different T atoms is not the same. Most of the compounds have a homogeneity range represented by RFe12−xTx. This homogeneity range is fairly large in the case of T=V and strongly asymmetric for T=Ti and W. A structure determination is given for a representative member of the RFe10Si2 family. This structure determination is compared with results obtained previously for T=Mo and V, in which latter compounds the site occupancy of the T component is completely different from that in RFe10Si2. A survey is given of the magnetic and invar properties of RFe10T2 compounds. Special attention is paid to an analysis of the magnetocrystalline anisotropy in these materials.
TL;DR: In this article, the ac field dependence of the polarization and strain responses of three different compositions of doped lead zirconate titanate ceramics were measured for samples in both the poled and depoled states.
Abstract: The ac field dependence of the polarization and strain responses of three different compositions of doped lead zirconate titanate ceramics were measured for samples in both the poled and the depoled states. The results indicate that a reversible domain wall excitation exists which contributes to the weak‐signal response of these materials. Irreversible domain wall motion can be excited within the frequency range measured by applying a field above a threshold field, which is much smaller than the coercive field. Therefore, the weak‐signal linear dielectric, piezoelectric, and elastic coefficients of these materials may not provide a suitable description of their behavior when the external applied field exceeds this threshold field. All the observed phenomena can be explained by thermally activated domain wall fluctuations and nucleations.
TL;DR: In this article, a model of twinned dendritic Terfenol-D was proposed, in which the magnetization of one twin jumps between two directions while the remaining twin undergoes a continuous rotation of the magnetisation.
Abstract: Large ‘‘jumps’’ in the magnetostriction have been observed in twinned single crystals of Tb03Dy07Fe19 (Terfenol‐D) for magnetic fields parallel to the crystalline [112] direction The interpretation of these large magnetostriction discontinuities is based upon a model of twinned dendritic Terfenol‐D in which the magnetization of one twin jumps between two [111] directions while the magnetization of the remaining twin undergoes a continuous rotation of the magnetization The field dependence of the magnetization and magnetostriction of cubic single crystals with λ111≫λ100 was calculated using an expression which included the anisotropy constants K1 and K2 and compressive loads along [112] With K1=−06 J/m3 and K2=−20 J/m3 (values appropriate for Terfenol‐D near room temperature), magnetization ‘‘jumping’’ is predicted For the twinned crystal, the jump in the magnetostriction was calculated to be greater than 1000 ppm Because of this large magnetostriction, it is possible to configure a device to p
TL;DR: In this paper, a magnet over a type II superconductor where the magnetic field at the superconducting disk exceeds Hc1 is described and shown to be stable over a flat disk; a complete Meissner effect would make this position unstable.
Abstract: Levitation of a magnet over a type II superconductor where the field at the superconductor exceeds Hc1 is described and shown. The penetration and pinning of the flux lines in the superconductor cause the position of the magnet to be stable over a flat disk; a complete Meissner effect would make this position unstable. Furthermore, the observed dependence of the height of levitation on such variables as the thickness of the superconducting disk and the size of the magnet are consistent with a model described in this paper based on the energy cost of flux penetration through vortices and inconsistent with a Meissner effect model.
TL;DR: In this article, a new approach to ionizing radiation detection is proposed, where the amount of ionization produced in a detector medium is measured by the heat generated as the charged carriers are drifted across the device under an applied voltage.
Abstract: A new approach to ionizing radiation detection is proposed. The amount of ionization produced in a detector medium is measured by the heat generated as the charged carriers are drifted across the device under an applied voltage. The amount of energy generated can be orders of magnitude larger than that deposited by the radiation itself. A dramatic increase in detector mass can be achieved compared to simple calorimetric particle detectors for equivalent energy thresholds. It is possible to obtain a sensitivity level sufficient for single‐carrier detection. The principle of operation has been demonstrated with an experimental device operated at a temperature of 1.8 K, and improved performance is expected at lower temperatures.