Search

Polar topological domain structures may have potential applications in future memory devices. Exploring their dynamical behaviors is paramount to the device design. Here, the meron–antimeron annihilation processes induced by the electric field in ultrathin ferroelectric PbTiO3 films were studied by phase-field simulations. Two types of annihilation behaviors were identified: The merons with central polarizations parallel to the electric field will directly annihilate with their nearby antimerons; those antiparallel to the electric field will first be switched and then annihilate with antimerons. The annihilation ratio of meron–antimeron pairs (MAPs) decreases with the increase in the meron–antimeron distance. During annihilation processes, the positions of antimerons seldom change and the merons approach to antimerons at some critical electric fields. The annihilation probability of a meron is found to be closely related to its topological charge. Specifically, the restoration of an MAP from a partially annihilated state was observed under the decrease in the electric field. These results may have some indications to the development of polar-meron-based memory devices. [ABSTRACT FROM AUTHOR]

Large compressive strains may introduce giant tetragonality and morphotropic phase boundaries in perovskite BiFeO3 films, where the coexisting tetragonal and rhombohedral phases (T like and R like phases) are identified to exhibit large piezoelectric response. Here, we have further achieved mechanical bending deformations in R like BiFeO3 through its neighboring T like BiFeO3 phases, where a strain gradient of ∼106/m was identified. Aberration-corrected scanning transmission electron microscopy revealed not only the strain distributions but also the atomic scale Fe polar displacement in the gradient R like BiFeO3. In spite of the giant strain gradient, the polarization direction in each R like BiFeO3 unit cell was found mainly along its diagonal direction, suggesting that potential flexoelectric coupling induced polarization in BiFeO3 is smaller than its spontaneous polarizations, while a large built-in electric field can be obtained via the large strain gradient. Our results indicate that the common phase coexistences in oxide materials could be further manipulated to introduce elastic strain gradients and tune the properties for oxide films. [ABSTRACT FROM AUTHOR]

It is known that high-index perovskite ferroelectric thin films exhibit giant permittivity, piezoelectric response, and a particular switching behavior. However, the fine domain configuration in high-index ferroelectric films is not yet clarified, which triggers difficulties to further modulate their electric properties. In this work, we focus on the tetragonal PbTiO3 thin films with thicknesses of 20, 40, 55, and 70 nm deposited on a [101]-oriented KTaO3 substrate. By using piezoresponse force microscopy and state-of-the-art scanning transmission electron microscopy, the stripe a/c domains with alternately wide c and narrow a domains are observed in all these PbTiO3 films. The periodic stripe a/c domains with {101} domain walls extend along the in-plane [ 11 1 ¯ ] or [ 1 1 ¯ 1 ¯ ] direction, which almost completely relaxes the misfit strain between the PbTiO3 films and the KTaO3 substrate. The domain width decreases as the film thickness is reduced following the square root dependence. This results in an increase of ferroelastic a/c domain walls and promotes the enhancement of the piezoresponse amplitude for the thinner PbTiO3 films. In addition, the piezoresponse amplitude of a 20 nm PbTiO3 film is comparable to that of a 40 nm PbTiO3 film, which indicates that the piezoelectric response of ferroelectric films may saturate at a certain film thickness and scarcely increase even after the film thickness reduces further. These results clarify the domain configurations of [101]-oriented PbTiO3 thin films and provide useful information for understanding the relationship between microstructures and piezoelectric properties in ferroelectric films. [ABSTRACT FROM AUTHOR]

Topological structures in ferroelectric materials play a crucial role in the potential applications of high-density memories and are currently the subject of intensive interest. Interfaces with local symmetry breaking have garnered wide attention in designing the topological domains in ferroelectric films by regulating the different boundary conditions. Here, we present multiple topological polar nanodomains near the heterointerfaces in the trilayered systems of BiFeO3/GdScO3/BiFeO3 grown on [110]-oriented TbScO3 substrates. The formation and stabilization of these topological polar states depend on the electrical and mechanical boundary conditions of the BiFeO3 layers. Aberration-corrected transmission electron microscopy observation reveals that the topological polar nanodomains, including nano-scale vortices and flux-closures at the termination of 109° domain walls and the semi-vortices at the end of 180° domain walls, are stabilized in the BiFeO3 layers confined by two orthorhombic structures. Furthermore, the formation of flux-closures near the BiFeO3/GdScO3 interface is influenced by the domain structures in the adjacent BiFeO3 layers, which is preferred by the 180° domain patterns rather than the 109° domain patterns. This work provides further understanding into the influences of boundary conditions on topological polar configurations and would offer guidance for designing novel topological states that enable the development of high-density memory devices. [ABSTRACT FROM AUTHOR]

Domain walls in ferroelectric materials attract great interest since they can possess fascinating functionalities. Therefore, it is very important to modulate domain structures. Our recent experiments showed that oxygen vacancy plates could induce charged domain walls with different types. However, the detailed transition behavior between different charged domain walls was not explored. In this work, systematical phase field simulations were performed to reveal the evolution of domain structures with the size and charge density of the oxygen vacancy plate. These results could provide a route to build complex patterns of charged domain walls. [ABSTRACT FROM AUTHOR]

Acoustophoretic assembly uses acoustic waves to move dispersed particles into a geometric pattern. The pattern is typically created in a single step and often relies on wave-forming techniques to achieve the desired pattern geometries. We show that multiple acoustic waves can be applied sequentially in a multi-step process to create particle patterns not achievable by the individual waves alone. We demonstrate this approach in spherical particles using two planar pseudo-standing waves. Applied individually, each of the two waves would create linear particle bands with uniform spacing in between the bands. However, when applied sequentially, the banding pattern created in the first step is further manipulated by the second wave to create non-uniform spacing in between the bands. The experimentally achieved particle pattern geometry agrees well with the theoretical prediction. [ABSTRACT FROM AUTHOR]

The atomic-scale mechanism of domain wall motion in ferroelectrics is commonly accepted to be nucleation and the movement of steps on the domain walls. Although very important in understanding the mechanism of domain wall motion and domain switching, the detailed atomic structures of steps have nevertheless been scarcely explored. In this work, the charged steps of these structures on 180° domain walls in PbTiO3 were investigated using first-principles computations. Contrary to the previous understanding that there is a sudden jump at a step from one atomic plane to an adjacent plane, our computation results suggest that it is actually a gradual transition and the actual steps lie at atomic planes with the approximate Miller indices (3 0 ...). A large polarization rotation was found around the steps, making the polarization distribution Ising–Néel-like. The barriers for the motion of steps along domain walls were found to be much lower than those for which the domain wall is moving as a whole. These findings provide valuable information for further investigations of the domain switching mechanism at the atomic scale. [ABSTRACT FROM AUTHOR]

The atomic-scale mechanism of domain wall motion in ferroelectrics is commonly accepted to be nucleation and the movement of steps on the domain walls. Although very important in understanding the mechanism of domain wall motion and domain switching, the detailed atomic structures of steps have nevertheless been scarcely explored. In this work, the charged steps of these structures on 180° domain walls in PbTiO3 were investigated using first-principles computations. Contrary to the previous understanding that there is a sudden jump at a step from one atomic plane to an adjacent plane, our computation results suggest that it is actually a gradual transition and the actual steps lie at atomic planes with the approximate Miller indices (3 0 ...). A large polarization rotation was found around the steps, making the polarization distribution Ising–Néel-like. The barriers for the motion of steps along domain walls were found to be much lower than those for which the domain wall is moving as a whole. These findings provide valuable information for further investigations of the domain switching mechanism at the atomic scale. [ABSTRACT FROM AUTHOR]

Anomalous Hall effect (AHE) has been studied for ferrimagnetic antiperovskite Mn4-xDyxN films grown by molecular-beam epitaxy. The introduction of Dy changes the AHE dramatically, even changes its sign, while the variations in magnetization are negligible. Two sign reversals of the AHE (negative-positive-negative) are ascribed to the variation of charge carriers as a result of Fermi surface reconstruction. We further demonstrate that the AHE current JAH is dissipationless (independent of the scattering rate), by confirming that anomalous Hall conductivity, σAH, is proportional to the carrier density n at 5K. Our study may provide a route to further utilize antiperovskite manganese nitrides in spintronics. [ABSTRACT FROM AUTHOR]

Determination of atomic and electronic structures of ferroelectric domain walls is crucial to understand and explore their unusual properties. Using first-principles calculations based on the density functional theory, we explored the atomic and electronic structures of 180° domain walls in PbTiO3, in order to understand the origin of Bloch-type polarization components. It is found that Bloch-type polarization components originate from the large displacements of Pb atoms and the Pb-O hybridization at the domain walls. The development of Bloch-type polarization components significantly reduce the domain wall energies and change the Peierls barriers of domain wall motion in different orientations. [ABSTRACT FROM AUTHOR]

Determination of atomic and electronic structures of ferroelectric domain walls is crucial to understand and explore their unusual properties. Using first-principles calculations based on the density functional theory, we explored the atomic and electronic structures of 180° domain walls in PbTiO3, in order to understand the origin of Bloch-type polarization components. It is found that Bloch-type polarization components originate from the large displacements of Pb atoms and the Pb-O hybridization at the domain walls. The development of Bloch-type polarization components significantly reduce the domain wall energies and change the Peierls barriers of domain wall motion in different orientations. [ABSTRACT FROM AUTHOR]

Single-phase and oxygen doped Mn2N0.86 thin films have been grown on MgO (111) by plasma-assisted molecular beam epitaxy. The films grow under tensile strain and, remarkably, they show ferromagnetic-like interactions at low temperature and ferromagnetic ordering agreed well with the Bloch-law T3/2 at room-temperature. We further demonstrate the enlarged Mn 3s splitting (6.46 eV) and its possible relation to the observed ferromagnetism. Our study not only provide a strategy for further theoretical work on oxygen doped manganese nitrides, but also shed promising light on utilizing its room-temperature FM property to fabricate spintronic devices. [ABSTRACT FROM AUTHOR]

The first concerned question on the fundamental physics of the resistive switching (RS) effect in metal/Nb-doped SrTiO3 junctions is whether the RS does take place at the whole interface or at some local regions of the interface. Even though several investigations provide the clues of the filamentary nature of the RS, direct evidences are still required. Moreover, there is obvious inconsistency between the possible filamentary feature and the observed capacitance-voltage (C-V) hysteresis loops. Here, we report direct evidences of a filamentary RS effect in Pt/Nb-doped SrTiO3 junctions. The virgin Pt/NSTO junctions show an initial RS effect. The current-voltage (I-V) characteristic of the initial RS and the C-V characteristic in the virgin junctions are interpreted by using the theory of metal/semiconductor contacts. The correspondence between the initial RS and the C-V hysteresis loops is also discussed. The most important is that an electroforming process is observed at a large forward voltage, which is a direct indication of the formation of conductive filaments across the Pt/NSTO interface. Following the electroforming, the Pt/NSTO junctions exhibit a filamentary RS effect. The I-V characteristic of the filamentary RS deviates from the theoretical prediction of metal/semiconductor interfaces. However, the C-V characteristic is almost the same as that of the virgin junctions. This demonstrates that the conductive filaments are formed at local regions of the Pt/NSTO interface and a majority of the interface remains invariant. The results clearly show that a filamentary RS effect occurs in the Pt/NSTO junctions and that the observed C-V hysteresis loops are not correlated to the filamentary RS. © 2014 AIP Publishing LLC. [ABSTRACT FROM AUTHOR]

Topological lattices such as vortices are of importance in both scientific research and application potential. Here, we observed periodic vortex-antivortex pairs in PbTiO3/SrTiO3 multilayered films deposited on orthorhombic (110)-oriented GdScO3 by pulsed laser deposition. Domain patterns of the PbTiO3 layers containing topological structures were analyzed in detail by using advanced transmission electron microscopy. It was found that by increasing the PbTiO3 thickness, a/c domains with extra c domains will form in the triangle a domains in pure flux-closure structures. Atomically resolved high-angle annular dark field-scanning TEM imaging demonstrates that this specific domain structure results in vortex-antivortex pairs at the junctions of extra c domains and the original flux-closure structure, forming a periodic vortex-antivortex array throughout the PbTiO3 layer. These results suggest a pathway for designing new topological structures in ferroelectric films. [ABSTRACT FROM AUTHOR]

We investigate the optical and electrical properties of a series of InAs/GaSb superlattices (SLs) as a function of InAs layer width d, from 21 to 55 Å, with a fixed GaSb layer width of 24 Å, corresponding to SLs with the cutoff wavelengths between 4 and 19 μm. Since the higher electron mass in InAs/GaSb SLs than in mercury cadmium telluride should lead to lower photodiode tunneling currents, we also measured the cyclotron effective mass for a very long wavelength infrared design SLs. For d<40 Å, the SLs were p-type, with hole mobilities of approximately 8 000 cm2/V s. For a high mobility p-type sample no hole cyclotron resonance signal was detected. However, the SLs with d≥40 Å were n-type, with electron mobilities increasing from 865 to 6126 cm2/V s. Cyclotron resonance data on an n-type SL sample yielded an electron cyclotron mass of 0.068 m0, which is three times the InAs bulk value of 0.023 m0. The mass enhancement was only partially accounted for by conduction band nonparabolicity, based on our 8×8 envelope function calculation. [ABSTRACT FROM AUTHOR]

The low-temperature reflectance spectra of a number of GaN epilayers with various impurity/defect concentrations and Hall mobility are systematically investigated in this paper. The interacting excitonic polariton model, considering both excitons A and B, is employed to reproduce the measured reflectance spectra of the GaN films, leading to the determination of the damping coefficients of the propagating polaritons in the films. It is shown that the impurity scattering plays a dominant role in the damping of the excitonic polaritons in the GaN epilayers with higher impurity concentrations at low temperatures, which is additionally supported by the photoluminescence and Hall measurements. [ABSTRACT FROM AUTHOR]

The experiments on the [t1Pt/0.4Co]5/(0.2–5.0)Ru/[0.4Co/t2Pt]5 (thickness unit is nm) multilayers with perpendicular anisotropy (PA) indicate that the interlayer coupling shows an antiferromagnetic (AF) and a ferromagnetic oscillatory behavior with the thickness of Ru spacer layers from 0 to 5.0 nm, and that the AF oscillations display a superposition of two different periods, which are 0.8 and 1.1 nm, respectively. Moreover, we found that the magnitude of AF coupling strength J is closely related to the magnitude of PA caused by varied thickness of nonmagnetic Pt layer. Our experimental results can be explained by Bruno’s electron-optics model. [ABSTRACT FROM AUTHOR]

The magnetization reversal in selected antiferromagnetically coupled multilayers has been studied by solving the Landau-Lifshitz-Gilbert equation. The multilayers are composed of 10 nmt[sub l]/3 nmt[sub 2]/10 nmt[sub 3], where t[sub 1], t[sub 2], and t[sub 3] are soft magnetic material and are separated each other by thin nonmagnetic spacers. Our results suggest that the coupled ternary layers can possess good permanent magnet properties: A coercivity of 5-6 KOe and a hysteresis loop which can become approximately rectangular with an appropriate choice of parameters. The coercivity in such coupled layers originates from the interlayer coupling and the demagnetization field between layers. [ABSTRACT FROM AUTHOR]

On the basis of a micromagnetic model, magnetization reversal in antiferromagnetically coupled (AFC) binary and ternary layers has been represented by computer simulation. Optimization of media parameters of the AFC layers has been done, especially for the effect of parameters, such as anisotropy and coupling magnitude, on the reversal. The results specify that easy axis dispersion rather than random anisotropy and a reasonably small anisotropy magnitude of the recording layer are required for obtaining large coercivity, small saturation field, and thermal stability in the AFC layers. The difference between the AFC binary and ternary structures is discussed briefly. [ABSTRACT FROM AUTHOR]

Sheet flow featured with shallow depth on vegetated slopes plays a key role on the dynamics of soil and water loss, yet the hydrodynamic characteristics of sheet flow pasting a vegetation stem simplified by an emergent cylinder have not been revealed. Laboratory flume experiments were conducted to investigate potential effects of a vegetation stem on velocity components, flow vortexes, and shear stress from time-averaged and time-resolved perspectives. Flow fields on the upstream flow of the cylinder at the symmetry plane were captured by using a high precision Particle Image Velocimetry (PIV, 63 pixel/mm) system. Four flow conditions with flow depths from 0.4 to 0.57 cm and cylinder Reynolds number from 2440 to 3806 were selected to fully evaluate the sheet flow condition. Time-averaged hydrodynamic features were analyzed in terms of streamlines, streamwise velocity, wall-normal velocity, and vorticity. Time-resolved features of two velocity components were then analyzed. Joint probability density functions of the two velocity components exhibited asymmetrical bimodal, indicating two preferred flow states occurred frequently, namely, backflow event and downflow event. Subsequently, analyses by linear stochastic estimation showed that the backflow event was induced by a reverse upstream flow starting from the leading edge of the cylinder and penetrating primary horseshoe vortex, which was motivated by the intermediate-flow mode proposed in previous open channel flow. Meanwhile, the downflow event was induced by a portion of fluid that was unable to penetrate the primary horseshoe vortex and then vertically impinged the flume bed, which was motivated by the downflow mode proposed in this study. As the critical hydrodynamic parameter for local scouring, shear stress was finally sketched. It was suggested that soil control measures should be implemented around the vegetation stem with a radius of 0.1D (D is the cylinder diameter), where the maximum shear stress mostly occurs. The newly defined flow mode could provide deeper insights into the mechanisms of sheet flow and promote the practice of soil erosion control on vegetated hillslopes. [ABSTRACT FROM AUTHOR]

Besides the negative longitudinal magnetoresistance (MR), planar Hall effect (PHE) is a newly emerging experimental tool to test the chiral anomaly or nontrivial Berry curvature in Weyl semimetals (WSMs). However, the origins of PHE in various systems are not fully distinguished and understood. Here we perform a systematic study on the PHE and anisotropic MR (AMR) of Td-MoTe2, a type-II WSM. Although the PHE and AMR curves can be well fitted by the theoretical formulas, we demonstrate that the anisotropic resistivity arises from the orbital MR (OMR), instead of the negative MR as expected in the chiral anomaly effect. In contrast, the positive MR indicates that the large OMR dominates over the chiral anomaly effect. This explains why it is difficult to measure negative MR in type-II WSMs. We argue that the measured PHE can be related with the chiral anomaly only when the negative MR is simultaneously observed. [ABSTRACT FROM AUTHOR]

Besides the negative longitudinal magnetoresistance (MR), planar Hall effect (PHE) is a newly emerging experimental tool to test the chiral anomaly or nontrivial Berry curvature in Weyl semimetals (WSMs). However, the origins of PHE in various systems are not fully distinguished and understood. Here we perform a systematic study on the PHE and anisotropic MR (AMR) of Td-MoTe2, a type-II WSM. Although the PHE and AMR curves can be well fitted by the theoretical formulas, we demonstrate that the anisotropic resistivity arises from the orbital MR (OMR), instead of the negative MR as expected in the chiral anomaly effect. In contrast, the positive MR indicates that the large OMR dominates over the chiral anomaly effect. This explains why it is difficult to measure negative MR in type-II WSMs. We argue that the measured PHE can be related with the chiral anomaly only when the negative MR is simultaneously observed. [ABSTRACT FROM AUTHOR]

Investigates the effect of copper, aluminum, silver doping into the platinum spacer layers on the perpendicular anisotropy and magneto-optical Kerr effect of cobalt multilayers. Experimental details; Results and discussion.

Presents information on a study which performed magneto-optical experiments on free and bound electrons in gallium (Ga) nitrogen (N) films and GaN/aluminum GaN heterojunctions. Experimental procedure; Results and discussion; Conclusion.

We present a microwave B-field scanning imaging technique using a diamond micro-crystal containing a nitrogen vacancy center that is attached to a fiber tip. We propose a pulsed modulation technique, enabling the implementation of a variety of pulsed quantum algorithms for state manipulation and fast readout of the spin state. A detailed mapping of the magnetic B-field distribution of a helical antenna with sub-100 μm resolution is presented and compared with numerical simulations. This fiber based microwave B-field probe has the advantages of minimized invasiveness and small overall size and will boost broad interest in a variety of applications where near field distribution is essential to device characterization, to name a few, antenna radiation profiling, monolithic microwave integrated circuit failure diagnosis, electromagnetic compatibility test of microwave integrated circuits, and microwave cavity field mode mapping. [ABSTRACT FROM AUTHOR]

The electronic structures of a representative rare earth monopnictide (i.e., DySb) under high magnetic field (i.e., in the ferromagnetic state) are studied from both experimental and theoretical aspects. A non-saturated extremely large positive magnetoresistance (XMR) is observed (as large as 3.7 × 104% at 1.8 K and 38.7 T), along with the Shubnikov-de Haas oscillations that are well reproduced by our first principles calculations. Three possible origins of XMR are examined. Although a band inversion is found theoretically, suggesting that DySb might be topologically nontrivial, it is deeply underneath the Fermi level, which rules out a topological nature of the XMR. The total densities of electron-like and hole-like carriers are not fully compensated, showing that compensation is unlikely to account for the XMR. The XMR is eventually understood in terms of high mobility that is associated with the steep linear bands. This discovery is important to the intensive studies on the XMR of rare earth monopnictides. [ABSTRACT FROM AUTHOR]

The exchange bias (EB) effect and magnetic domain structures of FeMnC/FeMn bilayers prepared by a facing target sputtering system were studied. Unusual doubly shifted hysteresis loops were observed in a series of FeMnC/FeMn bilayers when different magnetic fields were applied to induce the exchange bias. The temperature dependences of the double shifted loops were measured and the ferromagnetic resonance measurement reveals the existence of EB. The correlation between the microscopic domain structures and the magnetization reversal processes was discussed, which suggests that the domain structure distribution of the antiferromagnetic layer is responsible for the loop shift. [ABSTRACT FROM AUTHOR]

C-ion irradiation was performed on PtMn-based spin valves and the effects of ion irradiation on magnetoresistance (MR) and on the exchange field were investigated. When ion irradiation was performed prior to post-annealing, the exchange field was substantially enhanced after annealing, especially for an annealing temperature below 240 °C. The enhancement could be related to the formation of PtMn(C) phase, which might accelerate the formation of ordered PtMn phase and might increase the anisotropy of PtMn. Although the majority of C ions located in capping layers Ta and PtMn, small amounts of C ions may go into the interface of CoFe/Cu/CoFe, leading to a small MR. [ABSTRACT FROM AUTHOR]

Tunneling giant magnetoresistance (MR) of the Fe-Al[sub 2]O[sub 3] nanogranular films has been observed over a wide range of Fe volume fraction x and it took a maximum of 4.4% at room temperature for the film with x=0.45 at H=10 kOe. Furthermore, the field dependence of MR of the samples is well described by the form proportional to the square of the magnetization. Moreover, an estimate of the magnetic anisotropy energy density K[sub u] increases with the decrease of x, yielding a value 2 orders of magnitude greater than the value for bulk Fe when x=0.23. The Bloch's law, M[sub S](T)=M[sub S0](1-BT[sup b]), can also hold for all the samples but with nonbulk parameters dependent on the Fe volume fraction. These results reveal a percolation effect on the magnetic properties, as well as the conductance, in such nanogranular films. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

On the basis of a micromagnetic model, magnetization reversal in two antiferromagnetically coupled ferromagnetic layers (10 nm t[sub 1]/0.9 nmM/t[sub 2] nm films with t[sub 2]=2, 3, 4, 5 nm, here t[sub 1] and t[sub 2] are the top and bottom layers, respectively, and M the spacer) with the same random anisotropy arrangement can be represented by a computer simulation. The calculation indicates that the appearance of a full antiferromagnetic coupling at remanence requires the antiferromagnetic coupling constant j=-3.5 erg/cm[sup 2] for the 10 nm t[sub 1]/0.9 nmM/3 nm t[sub 2], films and it needs a large j value if t[sub 2] increases for the case of K[sub u2]=K[sub u1]=1x10[sup 6] erg/cm[sup 3] and M[sub s1]=M[sub s2]=400 emu/cm[sup 3]. H[sub c] follows the equation H[sub c]=-0.755j/M[sub s]t[sub 1] (j<0). Why the calculated H[sub c] values deviate from H[sub c][sup max]=-j/M[sub s]t[sub 1] is discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The TbCo/Si multilayers prepared by the rf magnetron sputtering system with various Si thickness have been investigated. X-ray diffraction, magnetic measurement and Kerr rotation have been performed. No antiferromagnetic coupling was found for the system. With the thickness of Si layer t[sub Si] increasing, the perpendicular anisotropy constant K[sub u], and the saturation magnetization M[sub s] decreased rapidly. It was assumed that Co[sub 2]Si and Tb had been formed in the interfacial zone between TbCo and Si layers due to the interlayer diffusion. The decreasing of M[sub s] is attributed to the decreasing of the effective thickness of magnetic layer. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Low-temperature heat capacity is systematically investigated in various glassy and crystalline polymorphs of a wide range of metallic glasses. We reveal that the boson heat capacity peak beyond the Debye level arises from both excess phonon scattering and background electronic excitation, and the two contributions are strongly coupled and also material-dependent. It is interesting to observe that the boson heat capacity peaks obey an inversely linear correlation between their heights and characteristic positions, which is mainly dominated by phonic anomalies. This indicates a universal structural softening among the studied glasses when the boson peak occurs. We further suggest a possibility that the linear evolution of the fast boson peaks can probe into the slow structural softening across the glass transition, and the two dynamic processes are controlled by the short-time shear modulus associated with local soft regions in fragile glasses. [ABSTRACT FROM AUTHOR]

Floating asymmetric circle and circle GaN microdisks are fabricated by using standard semiconductor techniques. Unidirectional ultraviolet whispering gallery mode lasing results from floating asymmetric circle GaN microdisks under optical pumping conditions at room temperature. The characteristics of the unidirectional whispering gallery mode lasing, including the lasing emission direction, threshold, emission intensity, and lasing mode number, are studied. A 2D finite difference time domain simulation on optical field distribution confirmed the resonance mechanism of whispering gallery mode lasing. This work is crucial for enhancing collection efficiency and facilitating the coupling of the electronic and photonic devices. [ABSTRACT FROM AUTHOR]

Flux-closure domain structures in ferroelectric thin films are considered to have potential applications in electronic devices. It is usually believed that these structures are stabilized by the depolarization field and the contact with electrodes tends to screen the depolarization field and may limit their formation. In this work, the influence of oxide electrodes (SrRuO3 and La0.7Sr0.3MnO3) on the formation of flux-closure domains in PbTiO3 thin films deposited on (110)-oriented GdScO3 substrates by pulsed laser deposition was investigated by Cs-corrected transmission electron microscopy. It is found that periodic flux-closure domain arrays can be stabilized in PbTiO3 films when the top and bottom electrodes are symmetric, while a/c domains appear when asymmetric electrodes are applied. The influence of asymmetric electrodes on the domain configuration is proposed to have a connection with their different work functions and conductivity types. These results are expected to shed light on understanding the nature of flux-closure domains in ferroelectrics and open some research possibilities, such as the evolution of these structures under external electric fields. [ABSTRACT FROM AUTHOR]

Reports on the behavior of the variation of the polar angle of the average magnetic moment in a terbium (Tb)/iron (Fe) multilayer as a function of temperature. Determination of the polar angle; Distribution of Tb and Fe concentrations.

Presents a study that investigated the static thermomagnetic recording properties of manganese-bismuth-aluminum thin films. Analysis of the magnetic-domain structures of the thin films; Examination of the write/erase cycles on the thin films; Effect of annealing on the write/erase performance of the thin films.

Reports the effect of aluminum doping into MnBiSi films on the structure and magneto-optical properties of the parent. Background to the study; Experimental details; Results and discussion.

Reports on the temperature dependence of the magnetic properties and interface magnetism of cobalt/platinum multilayers. Experiment conducted; Illustration of the temperature dependences of magnetizations; Conclusions.

Deals with a study wherein a type of domain structure observed in the annealed bismuth aluminum manganese silicon oxide films was described. Methods; Results; Discussion.

Presents a study that produced manganese (Mn)-bismuth (Bi)-aluminum thin films by sequential evaporation of the constituents. Temperature dependencies of the Kerr rotation angle; Composition dependencies of the absolute reflectivity; Factor that will make thin films retain the pure MnBi hexagonal structure.

Examines the accuracy of the local-density or local-spin-density approximations when applied to transition metals. Data on the calculated cohesive strategies of the transition metals; Issues which confront those who wish to employ band theory in studies of magnetism.

Exotic domain states, like vortex, offer the promise of superior properties and the potential disclination strain is a key factor for their formation in ferroelectrics. Here we show that large scale arrays of four-state vortex domains can be obtained in rhombohedral BiFeO3 thin films grown on PrScO3 substrates by pulsed laser deposition. Cs-corrected scanning transmission electron microscopy demonstrates that each vortex domain is comprised of four ferroelectric variants with two 180° domain walls and two 109° domain walls. Atomic mappings of the lattice distortions unit cell by unit cell reveal that the cores of the vortex might be charged. The strains are mainly concentrated on domain walls. The formation mechanism of such large scale vortex-like states was discussed. [ABSTRACT FROM AUTHOR]

An instrument used for measuring multiple scintillators' light output and energy resolution was developed. The instrument consisted of a light sensor array which was composed of 64 discrete SiPMs (Silicon Photomultipliers), a corresponding individual channel readout electronics system, and a data processing algorithm. A Teflon grid and a large interval between adjacent SiPMs were employed to eliminate the optical cross talk among scintillators. The scintillators' light output was obtained by comparing with a reference sample with known light output. Given the SiPM temperature dependency and the difference among each SiPM, a temperature offset correction algorithm and a non-uniformity correction algorithm were added to the instrument. A positioning algorithm, based on nine points, was designed to evaluate the performance of a scintillator array. Tests were performed to evaluate the instrument's performance. The uniformity of 64 channels for light output measurement was better than 98%, the stability was better than 98% when temperature varied from 15 °C to 40 °C, and the nonlinearity under 511 keV was better than 2%. This instrument was capable of selecting scintillators and evaluating the packaging technology of scintillator arrays with high efficiency and accuracy. [ABSTRACT FROM AUTHOR]

An inherent correlation between the strain rate sensitivity and α relaxation of metallic glasses (MGs) is observed. This correlation can be attributed to the secondary term which incorporates the nonaffine displacements of atoms in the analytical expression of the elastic modulus of amorphous solids. The observed correlation supports the proposition that stress and temperature play equivalent role in the glass transition of MGs. Besides, an ideal liquid state of MGs is observed in the supercooled liquid region when they are deformed below a critical loading rate. This observation would benefit the application of MGs in the fabrication of micro parts for MEMS (Micro Electro-Mechanical Systems). [ABSTRACT FROM AUTHOR]

Aluminum films were grown on SrTiO3 (100) substrates using a plasma-assisted molecular beam epitaxy system. We found that the intensity of defect emission coming through the Al films was enhanced to two fold. Although the surface plasmon energy is far from the defect emission, off-resonance enhancement is still possible from Al/SrTiO3. Moreover, the samples with Al films exhibits ferromagnetism, with wasp-waist hysteresis loops and exchange bias effects. The ferromagnetism may be attributed to the charge transfer between Al and the SrTiO3 matrix. This work is valuable in developing SrTiO3 which is a promising material used in optical and magnetic related application. [ABSTRACT FROM AUTHOR]

We report the linear thermal expansion behaviors of a Zr-based (Vitreloy 1) bulk metallic glass in its as-cast, annealed and crystallized states. Accompanying the glassliquid transition, the as-cast Vitreloy 1 shows a continuous decrease in the thermal expansivity, whereas the annealed glass shows a sudden increase. The crystallized Vitreloy 1 exhibits an almost unchanged thermal expansivity prior to its melting. Furthermore, it is demonstrated that the nucleation of crystalline phases can induce a significant thermal shrinkage of the supercooled liquid, but with the growth of these nuclei, the thermal expansion again dominates. These results are explained in the framework of the potential energy landscape, advocating that the configurational and vibrational contributions to the thermal expansion of the glass depend on both, structure and temperature. [ABSTRACT FROM AUTHOR]

An experimental study of the hole effective mass was conducted in a series of five remotely doped InSb quantum wells under biaxial compressive strain. From cyclotron resonance measurements at 4.2 K, an increase in hole effective mass was observed with increasing hole density in otherwise similar structures from 0.045me at 2.1×1011 cm-2 to 0.083me at 5.1×1011 cm-2. The smallest effective mass (0.017me) was observed in the quantum well with the largest compressive strain (1.05%) and narrowest well width (7 nm). Our measurements are in qualitative agreement with theoretical expectations. [ABSTRACT FROM AUTHOR]

In this paper different approximate boundary conditions (BC) describing a thin fiber-matrix interphase are used to study ultrasonic wave scattering from a multiphase fiber embedded in a solid matrix. To facilitate the analysis of scattering from a multilayered fiber, a matrix differential equation is derived for elastic fields in a cylindrical medium with radially-dependent properties. From this equation the transfer matrix for each intermediate layer between the fiber core and matrix, relating the stress and displacement fields on the inner and outer boundaries of the layer, is obtained. To describe the effect of the interphase the first- and second-order asymptotic and the spring boundary conditions are derived using an asymptotic expansion of the transfer matrix for a thin fiber-matrix interphase. Analysis performed for different models of spring boundary conditions shows the advantage of preserving the interphase gap connected by springs versus the spring BC defined on an infinitely thin interface, after eliminating the interphase layer and filling the remaining gap by matrix or fiber material. In the last two cases the geometry of the system changes due to change of the scattering surface radius, leading to error in the scattering amplitude. Numerical examples are given for scattering cross sections of longitudinal and shear waves from a multiphase SiC fiber in titanium. It is shown that the spring BC can be used to represent a thin interphase layer with elastic moduli smaller than those of the fiber. © 1997 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The scattering of an elastic wave obliquely incident on a multilayered cylinder in a solid is studied using a transfer matrix approach. Scattering of longitudinal and shear waves with arbitrary polarizations are considered. To facilitate the derivation of the solutions for scattering in the multilayered cylindrical system, a 6×6 transfer matrix is introduced for each cylindrical layer to relate the stresses and displacements on the inner and outer boundaries of that layer. A total transfer matrix relating the elastic field in the surrounding matrix to that in the cylinder core is obtained as a product of individual transfer matrices of intermediate layers. Numerical examples are given for a coated multiphase SiC fiber in a titanium matrix. Frequency and angle dependencies of specularly reflected and forward-scattered waves, and of the total scattering cross section, are calculated for different fiber-matrix interphase properties. © 1996 Acoustical Society of America. [ABSTRACT FROM AUTHOR]