ALBERT

Notes: The working frequency of Mn-Zn ferrites in switching power supply has been increased recently. Therefore, the manufacturing Mn-Zn ferrites with low loss at high frequency is very important. However, there were few reports concerning the core loss of Mn-Zn ferrites.1 It is beneficial to study the parameters affecting the core loss of Mn-Zn ferrites. Therefore, we studied the influence of atmosphere on the hysteresis loss (Wh) and eddy current loss (We) for different compositions in this work. Three compositions, Mn0.70Zn0.21−xFe2.09+xO4 (x=0, 0.01, 0.02), were prepared by traditional ceramic process. The sintering condition is 1385 °C for 4 h. Then, the samples are annealed at 1100 °C for 24 h in different oxygen partial pressure (0.015–1.0 vol %). Experimental results show that both We and Wh have minimum value at different oxygen partial pressure for samples with different composition. Increasing Fe content which raises the Fe++ concentration shifts the We and Wh minimum point to higher annealing oxygen partial pressure. It is mainly due to the oxidation of Fe++ and the transition of conduction mechanism, and it will be further discussed later. We can obtain the lowest core loss for using 10 and 100 kHz are samples with composition x=0 annealed in 0.07 and 0.2 vol % oxygen partial pressure, respectively. Summarily, for application to low loss at different working frequency, it is found that different optimized atmosphere should be controlled during annealing for different composition.

Notes: The effects of elastic strain induced by lattice mismatch on the effective mass and band offset at Γ point are studied in this article. We found that the effective masses (electron, light- and heavy-hole) become anisotropic in a strained layer. The theoretical calculations were made using a method of linear combination of atomic orbitals, and the overlapping integrals are adjusted in accordance with the change of atomic distance. In the kz direction, the effective mass ratios (strain: unstrain) of the electron of InxGa1−xSb/GaSb structure were found to vary from 1 to 3.38 for 0≤x≤1, the corresponding ratios of the light- and heavy-hole are 1 to 3.38 and 1 to 0.99, respectively. In the kx and ky direction, the ratios of the light- and heavy-hole are 1 to 1.02 and 1 to 1.13, respectively. For unstrained and strained interfaces, the band offset ratios of 90:10 and 57:43 (conduction band: valence band) are obtained, respectively. Experimental studies were also performed on the InxGa1−xSb/GaSb strained-layer superlattice sample. It was found that the theoretical calculations agree well with experimental results in this study.

Notes: We obtain undoped n-type GaSb epilayers by low-temperature metalorganic chemical vapor deposition at a low growth temperature of 450 °C reproducibly. Different conduction types of GaSb and different energy levels are compared by photoluminescence spectra. For n-type undoped GaSb, the FWHM of dominant peak and bound exciton are 11 and 1.3 meV, respectively. Because semi-insulating GaSb substrates cannot be obtained, we cannot use the Hall effect to determine the carrier concentration and mobility of the homoepilayer. In order to identify the conduction types of GaSb, ohmic contact and Schottky barrier are made by Au/Ge/Ni and Au, respectively. The concentrations of undoped n-type GaSb homoepilayers obtained from I-V and C-V measurements are 1.44×1017–3.0×1017 cm−3, respectively. The mobility and concentration of undoped p-type GaSb heteroepilayers are 758 cm2/V s and 9.0×1015 cm−3 at 300 K, respectively.

Notes: Undoped GaSb epilayers were grown on GaSb and GaAs substrates using the metalorganic chemical vapor deposition (MOCVD) technique, and photoluminescence (PL). Hall effect measurements were used to characterize the undoped epilayers. For undoped GaSb epilayers, four energy levels revealed by PL spectra are shown to be due to acceptors, using KTdp/dEf va Ef-Ev data obtained from Hall effect results, where p is the hole concentration, Ef and Ev are the Fermi level and the top of valence band, respectively. The acceptor levels lie at 3, 58, 80, and 130 meV above the top of valence band, respectively. The donor level is 15 meV below the bottom of the conduction band. These acceptor levels exist in almost all of the undoped p-type GaSb epilayers grown at high temperature, while the donor level exists only in the undoped n-type GaSb epilayers grown by low-temperature MOCVD. It is found that these levels may be changed using the different growth temperatures.

Notes: Single-phase Fe4N and (Fe1−xNix)4N compounds have been synthesized in a continuous form by heat treating iron and iron-nickel alloy sheets at various temperatures under NH3/H2 atmospheres. The Fe4N sheet has a high room-temperature magnetization value of 179 emu/g (2.14 μB/Fe), which is only slightly less than 218 emu/g (2.19 μB/Fe) observed in pure iron. The magnetic moments of the Fe-Ni alloy nitrides decreased monotonically as x was increased, in contrast to those for the starting alloys Fe1−xNix which exhibited a peak value around x=0.05. The decrease in magnetic moment with nickel content in the alloy nitrides was close to the value anticipated by magnetic dilution from nickel. The coercive force is about 5 Oe and is slightly decreased by the Ni substitution. The Fe-nitride offers a significantly improved corrosion resistance over pure iron. Even further improvement is obtained in the (Fe1−xNix)4N system with only slight sacrifice in magnetic moment. The addition of nickel has been found to noticeably improve the mechanical ductility of the normally brittle Fe4N compound. Theses nitrides also exhibit significantly increased electrical resistivity and wear resistance, and may be useful for a variety of technological applications.

Notes: We report here measurements of quasielastic neutron scattering from n-butane at temperatures of 90, 115, 125 and 190 K and in a momentum transfer range of 0.8–2.4 A(ring)−1. These measurements confirm that between 115 and 125 K butane forms a plastic crystal in which the centers of mass of the butane molecules form a crystalline structure, but the individual molecules are free to rotate. At these two intermediate temperatures, there exists both an elastic peak, characteristic of a solid structure, and quasielastic components arising from the rotational motions of the butane molecules. At 90 K, the butane scatters neutrons only elastically, while at 190 K, the butane scatters neutrons only quasielastically. In both the plastic and the liquid phases, the presence of at least two quasielastic processes must be assumed in order to explain the measurements. In the plastic crystal, we associate a broad Lorentzian component with intramolecular reorientations about the central carbon–carbon bond and a second, relatively narrow, Lorentzian component with whole molecule rotations.The latter process gives rise to a rotational quasielastic peak having a width of 400 μeV, which is constant to within the instrumental resolution of 70 μeV at both temperatures and at all measured momentum transfers. In a continuous diffusion model, this width corresponds to a rotational diffusion constant of 0.277 rad2/ps, a value which is about 3.5 times larger than one extracted from a molecular dynamics simulation of n-butane in the plastic phase recently published by Refson and Pawley [Mol. Phys. 61, 669 (1987); 61, 693 (1987)]. On the other hand, the first process, which corresponds to the carbon–carbon reorientation peak, is about 16 meV wide, indicating that this reorientation occurs on a time scale of about 0.1 ps. The absence of this broad peak in the solid butane at 90 K indicates that this fast carbon–carbon reorientation is coupled to an aspect of the structure or dynamics of the plastic phase. In the scattering from liquid butane at 190 K, there is a third, narrow quasielastic peak which also has a Lorentzian energy distribution. This peak width is about 200 μeV and corresponds to a translational diffusion constant of 0.23 A(ring)2/ps, a result in rough agreement with a recent molecular dynamics simulation of liquid butane by Ullo and Yip. [J. Chem. Phys. 85, 4056 (1986)].

Notes: The continuous inversion from a water-in-oil (w/o) microemulsion at low temperatures to an oil-in-water (o/w) microemulsion at higher temperatures within the one-phase channel of water (0.6% NaCl)–n-decane–AOT microemulsion system is investigated by small angle neutron scattering (SANS). At constant AOT (surfactant) weight fraction γ of 12%, the structural evolution as a function of temperature takes place in different forms as the oil-to-water weight fraction α is varied from 15 to 90 %. At low o-w weight fractions (α=15 and 20 %) the microemulsions transform from a water-internal, oil-continuous structure at lower temperatures to an oil-internal, water-continuous droplet structure at higher temperatures jumping across an intermediate region of a lamellar phase (Lα). However, at higher o-w weight fractions (α=80 and 90 %) the evolution goes through a stage of percolation of the water droplets first into extended water clusters, then the structural inversion takes place probably through a transition of these water clusters into an entangled tubular structure. At equal oil-to-water volume ration (α=40%), the structure can be described as bicontinuous at both low and high temperatures. In this case we are able to extract two lengths characterizing the structure from SANS data using different models for the scattering length density fluctuation correlation function of a bicontinuous microemulsion.

Notes: High-resolution, fast optical hole-burning results are reported for the amorphous system cresyl violet in ethanol glass at 1.3 K. Holes are burned and detected using a novel technique which allows precise detection of narrow (∼0.03 cm−1 ), shallow (∼1%) holes 10 μs to 50 ms after their generation. The technique is described in detail along with careful tests demonstrating the validity of its results. The hole width is observed to increase linearly with time when plotted against log time. Using the four time correlation function description of optical hole burning, the time-dependent increase in hole width (spectral diffusion) is shown to arise from a broad distribution of fluctuation rates in the glass with the probability of having a fluctuation at rate R proportional to 1/R. The 10 μs to 50 ms data is combined with hole-width data spanning the range 100 ms to 10 000 s and with two-pulse picosecond photon echo data. The two-pulse photon echo linewidth is calculated by extrapolating the fluctuation rate distribution obtained from the hole-width data to short times. The results are in excellent agreement with experimental echo results. The combined data from the two sets of hole-burning experiments provides a detailed description of the glass dynamics over nine decades of time, 10 000 s to 10 μs. Together with the two-pulse photon echo results, the data provide information on the glass dynamical behavior over seven decades faster in time as well. The net result is a description of the dynamics in low-temperature ethanol glass on time scales spanning 16 decades.

Notes: Extensive light scattering measurements, including the intensity, turbidity, and linewidth, on a three-component microemulsion system consisting of mixtures of water, decane, and a surfactant sodium di-2 ethylhexylsulfosuccinate (AOT) (WDA), have been made. The critical and several off-critical mixtures have been studied along constant microemulsion droplet volume fraction lines in the one-phase region over a very large temperature range. In the vicinity of the lower phase separation temperature Tp the intensity data are very well accounted for by the standard theory of critical binary fluids using a single value for the short range correlation length ξ0=(13.5±1.5) A(ring). By combining a mode-coupling theory including the background effects and a linear model equation of state applicable in the critical region, we have been able to fit the dynamic light scattering data using a Debye cutoff length q−1D which is equal to the constant average diameter of microemulsion droplets. Furthermore, we find clear evidence for a crossover from critical to single particle behavior in both static and dynamic light scattering data. A crossover temperature Tx has been identified at which qDξ(Tx)=1. Analyses of the dynamic light scattering data show that qD, which can only be measured far away from Tp, in fact plays a decisive role in controlling the critical dynamics in the whole temperature range.

Notes: In this article, the nonlinear characteristics of magnetostatic forward volume wave (MSFVW)-based guided-wave magnetooptic Bragg cell modulators in bismuth-substituted yttrium iron garnet-gadolinium gallium garnet waveguides using nonuniform bias magnetic field are reported. First, the dispersion characteristics of the MSFVW under nonuniform bias magnetic field are analyzed, and the explicit expression for its bandwidth is determined. The transmission measurements of the MSFVW show that owing to the nonuniform magnetic field, the bandwidth is significantly increased. Next, the results of noncollinear magnetooptic (MO) Bragg diffraction experiments using the MSFVW in the frequency range from 2.0 to 4.0 GHz are presented. Two types of nonlinear process, namely, the four-magnon decay and modulation instabilities, are observed. However, the MO experiments at the carrier frequency of 2.85, 3.10, and 3.25 GHz suggest that the decay instabilities did not play a significant role in the MO interaction because of the larger degree of phase mismatch induced by the satellite waves generated during the nonlinear processes. We find that despite the presence of the decay instabilities, the MO Bragg diffraction characteristics still comply with that predicted by the coupled-mode theory before the nonlinear processes evolve into the modulation instabilities. Once the four-magnon modulation instabilities set in at the threshold powers, the MO Bragg diffraction will incur a drop in diffraction efficiency by as much as 9%. This feature results from perturbation of the satellite waves of smaller wave numbers induced in the modulation instabilities that lead to the MO phase mismatch. A model is established to describe the combined contributions of the initial MSFVW and the excited satellite waves associated with the modulation instabilities to the MO Bragg diffraction characteristics. © 2000 American Institute of Physics.