GaMnSb/InGaAs/GaAs heterostructure leds with a ferromagnetic injector layer

A diode structure with a p-n junction and an InGaAs/GaAs quantum well in the space-charge region and a ferromagnetic GaMnSb layer as the p-type semiconductor has been fabricated and studied. The possibility of obtaining high-efficiency electroluminescence (EL) from the structure was demonstrated. It was found that the EL efficiency depends on the growth parameters of the ferromagnetic GaMnSb layer, i.e., the Mn content and layer thickness. The possible mechanisms of EL from the diodes under study were considered. Circularly polarized EL was obtained from the structures. It was shown that the degree of polarization (0.012 in a magnetic field of 0.37 T) remains nearly invariable in the temperature range 10?C50 K and the circular polarization of the emitted light is due to the injection of spin-polarized holes into the quantum well from the ferromagnetic GaMnSb layer.     

Structural studies of graphite intercalation compounds

Electron diffraction through the c-face (layer planes) and scanning electron microscopy (SEM) on the a-face (perpendicular to the layer planes) have been used to study the intralayer crystal structure and the micro-structure of graphite and its intercalation compounds. With the electron diffraction technique, the intra-layer intercalate ordering and the associated order-disorder transformations have been studied in graphitealkali metals (K, Rb, Cs) and graphite-halogens Br₂, IBr, ICl). Reported here is the first observation of order-disorder transformations in the graphite-halogen compounds. Direct evidence is given for the presence of intralayer intercalate ordering in even extremely dilute lamellar and residue compounds. Also presented here is a new a-face surface preparation technique, which involves mechanical polishing and back-sputtering. SEM observations of the a-faces reveal large microstructural differences between highly-oriented pyrolytic graphite, chemically-separated single-crystal graphite and mechanically-separated single-crystal graphite. Significant exfoliation along the c-direction occurs upon intercalation. Evidence is given for the preferential trapping of intercalate at defects in both lamellar and residue compounds. Work supported by United States NSF Grant #DMR 76-12226. This paper is based on a thesis submitted by the author in partial fulfillment for the Ph.D. degree in the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA, 1977 (unpublished).     

Model studies of extracellular electrograms arising from anexcitation wave propagating in a thin layer

Extracellular potentials were calculated for a wave of activation propagating through a thin layer of tissue. Sources were represented on the basis of the bidomain model, with the observation point at the tissue surface. Calculated potentials were found to be insensitive to the length of the wavefront if it passed under the recording electrode provided its length exceeded 1 mm, but to decrease rapidly when the wave passed to a side of the electrode. Contributions of source regions with a lateral displacement from the electrode greater than about 0.3 mm were substantially diminished. The effects of the thickness of the layer and velocity of propagation on amplitude was investigated.     

Experimental studies of magnetically scannable leaky-wave antennashaving a corrugated ferrite slab/dielectric layer structure

The radiation characteristics of a magnetically scannable leaky-wave antenna using a corrugated ferrite slab supported by a Teflon waveguide have been demonstrated experimentally. A corrugated polycrystalline yttrium iron garnet (YIG) slab having the dimensions 150.0 mm×15.0 mm×10 mm has been fabricated. The corrugation depth, corrugation spacing, and number of corrugations are 150.0 μm, 2.0 mm, and 55.0, respectively. Experiments have been carried out in the millimeter-wave frequency range from 40.0 to 50.0 GHz. The main beam direction of the leaky wave shifts continuously about 41.0° at the operating frequency 46.8 GHz by altering the DC magnetic field up to 1.4 T. It is found that the corresponding half-power beamwidth varies from 3.2° to 3.6° and a maximum scanning rate is 1.0°/0.02 T. Experimental results are compared with theory based on the dispersion relation of the ferrite slab/dielectric layer structure     

Structural and optical properties of GaAs(100) with a thin surface layer doped with chromium

The aim of this study is to explore the structural and optical properties of single-crystal GaAs(100) doped with Cr atoms by burning them into the substrate at high temperatures. The diffusion of chromium into single-crystal GaAs(100) substrates brings about the formation of a thin (~20–40 μm) GaAs:Cr transition layer. In this case, chromium atoms are incorporated into the gallium-arsenide crystal lattice and occupy the regular atomic sites of the metal sublattice. As the chromium diffusion time is increased, such behavior of the dopant impurity yields changes in the energy structure of GaAs, a decrease in the absorption at free charge carriers, and a lowering of the surface recombination rate. As a result, the photoluminescence signal from the sample is significantly enhanced.     

Si衬底GaN基多量子阱外延材料的TEM研究

本文采用高分辨透射电子显微技术对在Si衬底生长的GaN基多量子阱外延材料的位错特征、外延层与衬底的晶体取向关系及界面的结晶形态等微观结构进行了分析和研究.结果表明:Si衬底生长的GaN与衬底有一定的取向关系;材料在MQW附近的穿透位错密度达108 cm-2量级,且多数为刃型位错;样品A的多量子阱下方可见平行于界面方向的...     

铁磁性微晶玻璃的制备

采用熔融法制备了SiO_2-Na_2O-CaO-P_2O_5-Fe_2O_3系微晶玻璃。制备过程中磁铁矿晶相在玻璃自然冷却时自然析出,故不需要对玻璃进行核化和晶化等热处理。利用XRD确定了样品晶相组成并计算了样品中晶体的晶格常数和晶粒度,采用振动样品磁强计(VSM)测试了样品的磁性能。结果表明:所制微晶玻璃只含有磁铁矿晶相并具有生物活性;Fe_2O_3质量分数为45%的样品性能最佳,其比饱和磁矩为20.24A·m~2/kg,内禀矫顽力H_(cj)为7kA/m。     

Structural studies of Langmuir-Blodgett films: technology and analysis

Using the Langmuir-Blodgett technique, ultra-thin films of organic molecules can be deposited on suitable substrates with a high degree of precision over the individual layer thickness. The electronic and optical properties of these films are closely related to the molecular orientation within the layer. Some of the techniques used to analyse the structure of the floating and transferred layers are discussed in this short review, with special reference to phthalocyanine films     

Normal modes of a ferromagnetic laser with one Brewster face

Normal modes are determined for a solid-state laser constructed with one Brewster angle face that incorporates a gyrotropic host crystal. It is shown that, depending on the amount of Faraday rotation down the length of the crystal, the modes may be either linearly or elliptically polarized. Values for reflection loss and resonant frequency are determined. These calculations may be used to determine optimum conditions for modulation of amplitude, polarization aspect, and frequency of the output of a YIG laser.     

Real-time MRI-based control of a ferromagnetic core for endovascular navigation

This paper shows that even a simple proportional-integral-derivative (PID) controller can be used in a clinical MRI system for real-time navigation of a ferromagnetic bead along a predefined trajectory. Although the PID controller has been validated in vivo in the artery of a living animal using a conventional clinical MRI platform, here the rectilinear navigation of a ferromagnetic bead is assessed experimentally along a two-dimensional (2D) path as well as the control of the bead in a pulsatile flow. The experimental results suggest the likelihood of controlling untethered microdevices or robots equipped with a ferromagnetic core inside complex pathways in the human body.     

Berezinskii-Kosterlitz-Thouless phase transition in a 2D-XY ferromagnetic monolayer

It has been widely discussed whether long-range magnet-ic order could exist in low-dimensional (d ＜ 3) systems.Early studies,like Hohenberg-Mermin-Wagner theorem based on the Heisenberg model of magnetism,incline to a negative con-clusion,as the thermal fluctuation at any finite temperature prevents the formation of long-range magnetic order[1,2].However,further studies theoretically predicted an unusual long-range magnetic order in the two-dimensional (2D) sys-tems that are described by a so-called 2D-XY model,result-ing from the formation of bound pairs of vortices and anti-vor-tices with opposite chirality[3,4].The induced ferromagnetism is suppressed as the 2D system is heated over a critical temper-ature,accompanied with the destruction of those bound pairs and thus the long-range magnetic order.This mechan-ism of phase transition is known as Berezinskii-Kosterlitz-Thou-less (BKT) formalism[3-5].     

A rotating ferromagnetic sphere as a source of long-wavelength electromagnetic radiation

A ferromagnetic sphere rotating with constant angular velocity ω₁ is considered when the directions of magnetization vector M applied external magnetic field H and rotation frequency ω₁ do not coincide. The intensity of electromagnetic waves radiated by this sphere is found. It is shown that the radiation is strongly anisotropic and nonstationary.     

Linear and nonlinear EMP diffusion through a ferromagnetic conducting slab

The penetration of an EMP field, such as a plane-wave incident upon and a surge-arrestor current terminated at a shielding plate, through a ferromagnetic conducting slab made of iron or steel is investigated. The diffusion of the electromagnetic field in the highly conducting slab is complicated by the presence of the nonlinear saturation of the ferromagnetic permeabilitymu, due to the large amplitude of the incident EMP. Such a saturation, compared to the no-saturation constantmucase, makes the field diffuse faster in the slab and admits a stronger penetration field inside the shielding if the slab is thin and the pulse duration is long, as expected. On the contrary, if the slab is thick and the puslewidth is short, as the practical cases are, the saturation reduces the penetrated field but maintains its time shape. In this report, first we solve analytically the one-dimension plane-wave incidence problem for a slab with a constantmu. Then we use the results to partly predict and to interpret the numerical values obtained by using a finite difference code for the case of a nonlinearmu. These comparisons reveal excellent agreement. Second, we solve the constantmu, cylindrical-wave incidence problem by an approximate but extremely useful analysis, with its validity parameters clearly established. The results, shown to bear a simple relationship to those for the one-dimension problem, enable one to make use of the one-dimension results and predict easily the penetrated fields caused by a cylindrical incident current. Then for the nonlinear-mucase, we justify and extend that relationship by which the behaviors of the cylindrically diffused fields are obtained from those numerical results of the one-dimensional problem.     

Structural and electrical properties of HfO2 with topnitrogen incorporated layer

A novel technique to control the nitrogen profile in HfO₂ gate dielectric was developed using a reactive sputtering method. The incorporation of nitrogen in the upper layer of HfO₂ was achieved by sputter depositing a thin Hf_xN_y layer on HfO₂, followed by reoxidation. This technique resulted in an improved output characteristics compared to the control sample. Leakage current density was significantly reduced by two orders of magnitude. The thermal stability in terms of structural and electrical properties was also enhanced, indicating that the nitrogen-doped process is effective in preventing oxygen diffusion through HfO₂. Boron penetration immunity was also improved by nitrogen-incorporation. It is concluded that the nitrogen-incorporation process is a promising technique to obtain high-k dielectric with thin equivalent oxide thickness and good interfacial quality     

Dispersion characteristics of magnetostatic surface waves in a two-layer ferromagnetic film

The dispersion characteristics (dispersion and isofrequency curves and dispersion surfaces) of magnetostatic surface waves propagating in an arbitrary direction in a two-layer ferromagnetic film are investigated. The shapes of these curves and surfaces are studied at different ratios between the saturation magnetizations of the ferromagnetic layers, and the conditions for existence of external waves (always forward) and internal waves (forward and backward or only forward) are determined.     

Analysis of coupled microstrip lines on a layered substrate containing a metal ferromagnetic film

A method is described for the numerical analysis of the fundamental electromagnetic waves in an open planar multiconductor transmission line on a layered substrate containing a thin metal ferromagnetic film. Matrices of the inductance and capacitance per unit length of the strip conductors are obtained via rigorous solution of 2D magnetostatic and electrostatic boundary-value problems. Formulas for calculation of the phase velocities of quasi-TEM modes and corresponding amplitudes of currents and voltages on the strip conductors are derived.     

Propagation properties of ferromagnetic insulator guide

In order to realize new ferrite planar devices for applications at millimeter-wavelength frequencies, the authors have developed nonreciprocal ferrite devices schemes for incorporating ferromagnetic layers in dielectric insulator guide geometries. Their research program involves both the calculation and the measurement of device characteristics. For the calculation, a method of effective permeability, in which the permeability is a tensor, is introduced to characterize the ferrite material. The propagation properties of the insular guide are calculated by using a single-mode approach. The calculated results for dispersion, dielectric, and conductivity losses show resonant behavior with the application of a magnetic bias field for a guide configuration in which the ferrite replaces the insular dielectric. Ferrite phase shifters, filters, isolators, and circulators are potential applications of this guide configuration. For the experimental part of the study, wave dispersion and attenuation were measured in a purely dielectric insular guide from 26.5 to 40GHz. In addition to these experiments wave attenuation was measured as a function of magnetic bias field for the case where a hexagonal ferrite platelet was mounted on the ground plane near the insulator guide. General agreement is found between calculated and measured attenuation     

Electromagnetic response of a thin layer

The detectability of a thin layer within a stratified medium is considered. The two limiting cases of a resistive and a conductive sheet are discussed for both TM (transverse magnetic) and TE (transverse electric) excitation. It is shown that the resistive sheet is only `visible? for the TM excitation.     

New nonlinear magnetostatic surface waves in a ferromagnetic (YIG)

The general propagation characteristics of magnetostatic surface waves guided by a single interface of a semi-infinite nonlinear dielectric cover and a ferromagnetic substrate (YIG) have been derived. The nonlinear dielectric cover has intensity dependent refractive indices. The magnetostatic approximation is considered and retardation is ignored in describing the electromagnetic fields in the structure. The used magnetostatic approximation is leading to new waves and might be called nonlinear magnetostatic surface waves. The propagation of these waves is non-reciprocal in contrast to the linear magnetostaic surface waves, which had been only found in the negative direction of propagation.     

Surface magnetoplasma waves in a ferromagnetic semiconductor and their excitation by a magnetic dipole

Natural oscillations of an electromagnetic field at the boundary of free space with a ferromagnetic semiconductor are studied. The corresponding dispersion law and the domain of existence are determined. It is shown that these oscillations can be excited by a magnetic dipole located above the surface of the conducting medium. The fields and energy-flux density of surface waves in free space are calculated.