摘要:

A steady, collective translation of domain walls has been detected through direct wall observations in metallic ferromagnets subjected to a constant temperature gradient. A 60‐Hz ac external fieldHEis used to reduce the effect of pinning forces on the walls. Three driving mechanisms, Nernst–Ettinghausen mechanism, end‐drive mechanism, and isothermal end‐drive mechanism, are proposed. Three pinning mechanisms, bulk pinning, surface pinning, and end pinning are believed to be effective in these materials. The region in the (dT/dx,H0E) plane corresponding to static walls has a triangular shape. We have generalized the theory to include the three pinning wells, and the corresponding theoretical phase diagrams are shown. The saturation of phase boundary is also discussed.

ISSN:0021-8979    

DOI:10.1063/1.336517

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Ferromagnetic domain walls are observed to move from the hot to the cold end of samples of amorphous (Co92.5Fe7.5)78Mo2B15Si5subjected to a constant temperature gradientdT/dx. An ac magnetic fieldH0Eparallel to the easy axis is used to decrease pinning forces on the walls. The critical temperature gradient (dT/dx)crequired to move walls is of order 102K/mm. The linear decrease of (dT/dx)cwith increasingH0Eindicates that pinning of the walls by the two ends of the sample is dominant over bulk pinning. The dependence of (dT/dx)con sample length and thickness indicates that the Nernst–Ettingshausen drive mechanism is dominant over competing drive mechanisms. The speed of walls has been measured and is found to increase with increasing temperature gradient.

ISSN:0021-8979    

DOI:10.1063/1.336518

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Amorphous Tb‐Fe thin films prepared by dual magnetron cosputtering were exposed to air at 200 °C in order to investigate the evolution of the films as they oxidize. Magnetic properties of the films were measured using a vibrating‐sample magnetometer and torque magnetometer and are interpreted in light of the structure of the films as revealed by Auger electron spectroscopy and composition‐depth profiling. This leads to a detailed and self‐consistent description of the oxidation process. At first a uniform and homogeneous oxidation layer grows from the surface toward the substrate. This layer has a high magnetization and low intrinsic anisotropy and consists of an intimate mixture of oxidized Tb and metallic TbxFe(1−x). The initially high intrinsic anisotropy of the unoxidized region decreases relatively quickly, while the composition changes only slowly as this region shrinks. When the oxidation layer reaches the substrate, two oxide phases (Fe2O3and Tb2O3) begin to grow at the surface exposed to air.

ISSN:0021-8979    

DOI:10.1063/1.336519

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A new rapid solidification processing technique, liquid dynamic compaction (LDC), has been used to make bulk permanent magnets of composition Fe57Co20Nd15B8. In this process, molten metal is spray atomized onto a cooled substrate in a protective atmosphere. Oxidation is minimal. Subsequent heat treatment at 450 °C of the LDC’d material has resulted in isotropic permanent magnets with intrinsic coercivity and remanance approaching 8000 Oe and 6000 G, respectively.

ISSN:0021-8979    

DOI:10.1063/1.336520

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Love‐type surface waves in thin‐film coatings on a piezoelectric half‐space of the (622) crystal class are studied. Silver and gold coatings are used on the piezoelectric half‐space, and numerical results are obtained for the relationship between the velocity and the wave number. Surface waves by thin‐film coatings on both sides of an infinite piezoelectric plate of the (622) crystal class are also studied. The dispersion equation has been solved for a given velocity to obtain the wave number numerically.

ISSN:0021-8979    

DOI:10.1063/1.336521

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Heavily phosphorus or gallium‐doped silicon was grown by liquid‐phase epitaxy and studied by photoluminescence. For the phosphorus‐doped samples grown from In(P) solution, recombination of free electrons to compensating In acceptor levels was observed besides the free electron‐free hole band‐to‐band emission. The gallium‐doped samples showed a luminescence spectrum similar to the one observed in bulk‐dopedp‐type material, indicating a good crystalline quality and low compensation in these samples. The band‐gap shrinkage was found to be larger in heavily gallium‐doped than in boron‐doped silicon, indicating a dependence of this shrinkage on the chemical nature of the dopant atoms.

ISSN:0021-8979    

DOI:10.1063/1.336522

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Rate equations for the densities of free excitons and excitons bound to two different neutral acceptors in silicon are solved for steady state in the absence of saturation. These rate equations explicitly include terms for forward and reverse tunneling of bound excitons from one type of neutral impurity to another. Both tunneling rates are calculated using a simple model of an exciton in a one‐dimensional semi‐infinite double potential well. The steady‐state solutions of the rate equations yield an expression for the ratio of the bound exciton luminescence intensity as a function of the impurity concentrations. The relative photoluminescence intensities for the systems Si: (B, In), Si: (Al, In), Si: (Ga, In), Si: (B, Al), Si: (B, Ga), and Si: (Al, Ga) are calculated for the relevant free‐exciton capture cross‐section ratios. This model predicts no exciton tunneling for any of the above systems for the low‐impurity concentration range of 1012–1013 cm−3. For those systems with large differences in the bound exciton energy levels such as Si: (B, In), Si: (Al, In), and Si: (Ga, In), and having indium concentrations exceeding 1015 cm−3, it predicts quenching of shallow impurity bound exciton luminescence because the forward exciton tunneling rate from the shallow level to the deep level of indium dominates and the reverse exciton tunneling rate from indium to the shallow impurities is negligible. For the systems with small differences in the bound exciton energy levels such as Si: (B, Al) and Si: (B, Ga), the theory predicts enhancement of shallow impurity bound exciton luminescence beyond certain concentrations depending upon the free‐exciton capture cross‐section ratios because in these cases the reverse exciton tunneling rate dominates. For the system Si: (Al, Ga) in which the difference in the bound exciton energy levels is very small, gallium bound exciton luminescence dominates when the gallium concentration exceeds 1016 cm−3.

ISSN:0021-8979    

DOI:10.1063/1.336523

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A simple method is demonstrated for obtaining the thermal diffusivity of solids, by measuring the phase lag between a front and rear illumination, at a single chopping frequency. The method is tested using some semiconductor and glass samples.

ISSN:0021-8979    

DOI:10.1063/1.336524

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The thermal decomposition of disilane (Si2H6) in a hydrogen or helium flow has been used for the deposition of hydrogenated amorphous‐silicon (a‐Si:H) films on the surface of Corning 7059 glass substrates at 450–500 °C. The reaction product consists of monosilane and trisilane in addition to the unreacted disilane and ethylsilane (the major impurity in commercial disilane). The concentration of Si2H6in the reaction mixture has been found to strongly affect the deposition rate and the photoconductivity ofa‐Si:H films. At a given Si2H6concentration, the deposition rate ofa‐Si:H films increases exponentially with temperature. At a given substrate temperature, the AM1 conductivity ofa‐Si:H films increases with increasing Si2H6concentration and approaches 10−5&OHgr; cm−1at Si2H6concentrations higher than about 4%, and the conductivity ratio in better films is about 105. The conductivities of CVDa‐Si:H films have been found to show negligible change under illumination over a period of several days. The optical band gap ofa‐Si:H films has been determined to be 1.65–1.68 eV. The doping ofa‐Si:H films with arsenic and boron has been carried out, and their activation energies determined.

ISSN:0021-8979    

DOI:10.1063/1.336525

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

The absorption of CO2laser radiation inp‐type GaAs is dominated by direct free‐hole transitions between states in the heavy‐ and light‐hole bands. For laser intensities on the order of 10 MW/cm2, we report that the absorption associated with these transitions in moderately Zn‐doped GaAs (∼1017cm−3) begins to saturate in a manner predicted by an inhomogeneously broadened two‐level model. At higher laser intensities surface melting occurs initially at localized sites in moderately doped material and more uniformly in heavily Zn‐doped samples (≳1018cm−3). As the energy density of the CO2laser radiation is progressively increased further, the surface topography of the samples shows signs of ripple patterns, high local stress, vaporization of material, and exfoliation of solid GaAs fragments. Electron‐induced x‐ray emission data taken on the laser‐melted samples show that there is a loss of As, compared to Ga, from the surface during the high‐temperature cycling. By irradiating the samples in air, argon, and vacuum, we find that the vaporization rates are directly influenced by the ambient environment, particularly by the interaction of oxygen with the molten GaAs. Secondary ion mass spectrometry measurements are used to study the diffusion of oxygen from the native oxide and the incorporation of oxygen in the near‐surface region of the GaAs samples that have been melted by a CO2laser pulse. We find that oxygen incorporation does occur, and that the amount and depth of the oxygen incorporation depends on the laser energy density, number of laser shots, and ambient environment. For samples that are irradiated in argon or vacuum, we find that removal of the native oxide can be accomplished with CO2laser pulses. Similar measurements are performed on Si‐implanted GaAs, and results are reported for the redistribution of the implanted silicon atoms, the deviations from stoichiometry, and the incorporation of oxygen in the resolidified layer.

ISSN:0021-8979    

DOI:10.1063/1.336526

出版商:AIP    

年代:1986

数据来源: AIP