Increase In Domain Size Research Articles

Magnetoresistance of granular ferromagnets—observation of a magnetic proximity effect?

We have observed a superparamagnetic to ferromagnetic transition in films of isolated Ni grains covered by non-magnetic overlayers. The magnetoresistance (MR) of the films was measured as a function of the overlayer thickness. Initially, the granular Ni films exhibited negative MR curves peaked at H=0. As different materials were deposited onto the grains hysteresis developed in the MR. This behavior is ascribed to an increase of the typical domain size because of the magnetic coupling between grains. The strength of the inter-grain coupling is found to correlate with the magnetic susceptibility of the overlayer material. We discuss possible mechanisms for this coupling and suggest that the data may reflect the existence of a magnetic proximity effect (analogous to the well-known effect in superconductivity) in which a ferromagnetic moment is induced in the metallic non-magnetic medium.

Confocal Scanning Laser Microscope Image of Gradient Structure Formed in an Acrylate Copolymer/Fluoro-copolymer Blend

Thin films of poly(2-ethylhexyl acrylate-co-acrylic acid-co-vinyl acetate)/poly(vinylidene fluoride-co-hexafluoro acetone) [P(2EHA-AA-VAc)/P(VDF-HFA)] of 30/70 (by weight) blends without and with addition of 2 wt% fine silica gel were prepared on poly(ethylene terephthalate) (PET) from 20 wt% THF solution. Gradient domain morphology formed in the 30/70 blend was observed with a confocal scanning laser microscope (CSLM). Separate domains composed of P(2EHA-AA-VAc) phase were found in P(VDF-HFA) matrix at various levels of increasing depth with increasing domain size. Thus, CSLM is quite effective in morphological observation of the gradient structure formed in polymer blends, provided the blends are transparent.

Design for low noise double layered perpendicular magentic medium

Noise property and noise origin for double layered perpendicular magnetic recording media were studied in terms of the medium design and fabrication. It was found that medium noise from recording layer increased by introducing a soft magnetic backlayer. This might due to increase of a magnetic domain size of recording layer. In a Co-Cr system, some intermediate layers were found to reduce the medium noise of the recording layer. The still remained noise was thought due to the magnetization irregularity of the head-on like transition in the backlayer that was affected by the recording layer magnetization.

Optical properties of single crystals and vacuum-deposited thin films of a substituted oligo( p-phenylene vinylene)

The optical properties and structural organization of a 5-ring n-octyloxy-substituted oligo( p-phenylene vinylene) have been investigated in the solid state. For this study solution-grown single crystals and vacuum-deposited thin films were used. The unit cell of the solution-grown single crystals was determined to be monoclinic, space group I2 a . The as-deposited oligomer films showed a polycrystalline structure. Annealing the film at a temperature of 120°C resulted in a morphological change, which manifested itself in an increase of crystalline domain size from approximately 4 μm to 20 μm. Both single crystals and thin films exhibit a high photoluminescence quantum yield of 0.5 and 0.7, respectively. In order to determine the relative importance of oxygen and water on photoluminescence quenching, we measured the luminescence decay of a vacuum-deposited film exposed to water and air. It was found that quenching is mainly due to contamination with oxygen from air rather than water and that this contamination is reversible to a great extent. We demonstrate that under intense laser excitation it is possible to obtain stimulated emission from both single crystals and thin films. Non-optimized single-layer light-emitting diodes prepared from the oligomer showed uniform green/yellow light emission with external electroluminescence efficiencies up to 0.15% using Ca as electron-injecting electrode. The electroluminescence efficiency is drastically increased by annealing.

Kinetics of Spinodal Decomposition in Liquid Crystalline Polymers: Processing Effects on the Phase Separation Morphology

Results from a Landau−Ginzburg model which treats the problem of spinodal decomposition of liquid crystalline polymers (LCPs) in solution are presented. Morphological evolution of one conserved order parameter (polymer volume fraction) and one nonconserved order parameter (the Flory orientational order parameter) is considered. Processing effects on morphology including quench temperature, composition, solvent quality, and molecular weight are presented. Simulations of example quenching experiments demonstrate that increased LCP concentration, decreased molecular weight, increased solvation, and decreased quench depth all lead to increased domain size. Implications of the model regarding the optimization of processing conditions for LCP fiber spinning and film casting are discussed.

Effect of tempering on the microstructure and strength of martensitically hardened plain carbon steels

The X-ray interference line profile analysis was applied to plain carbon steels with 0.4 wt.% carbon after martensitic hardening and tempering in order to investigate the mean strains and domain sizes. From these parameters micro residual stresses and dislocation densities have been estimated. The mean strains of the hardened samples are only caused by the stress fields of dislocations. Tempering leads to decreasing mean strains and micro residual stresses as well as increasing domain sizes due to rearrangements and annihilations of dislocations. The hardening contributions of dislocations and carbide particles in the yield strength of the quenched and tempered states which increase with increasing carbon content, are evaluated.

Effects of First‐Order Approximations on Head and Specific Discharge Covariances in High‐Contrast Log Conductivity

The hydraulic head and the specific discharge fluctuations depend nonlinearly on the hydraulic conductivity. However, the methods most commonly used in the stochastic analysis of groundwater flow are based upon the linearization of these relations. In this paper we apply a numerical spectral approach to investigate the range of validity of the small perturbation approximation for head and specific discharge moments in two‐dimensional finite domains. We find that the small perturbation approximation tends to underestimate the variance of large‐scale head and specific discharge fluctuations and error increases with increasing log‐conductivity variance and increasing domain size. The head fluctuations do not appear ergodic even when the small perturbation approximation predicts they will be ergodic. The specific discharge fluctuations, on the other hand, do appear ergodic. The small perturbation approximation performs well in estimating specific discharge variance in the longitudinal direction but significantly underestimates transverse specific discharge variance.

Effect of titanium substitution on the structure and properties of Fe3Al-based intermetallic alloys

Substitutions (0–16 at%) of titanium for iron in Fe3Al-based alloys rapidly solidified by chill-block melt-spinning stabilize the D03 and B2 ordered structures. Rapid solidification results in total suppression of D03 order in binary alloys, whereas alloys containing titanium have D03 structure. D03 and B2 antiphase domain size, lattice parameter and hardness increase with increasing titanium content of the alloy. The deformation mode changes from single (unit) bcc dislocation in binary alloys to two-fold superdislocation configuration in D03Fe3Al-Ti alloys. Mechanical antiphase boundaries are generated by the movement of these imperfect configurations. All the alloys exhibited cleavage tensile failure. The mechanical properties are correlated with the observed structural changes.

Designed Synthesis of Solid State Structural Isomers from Modulated Reactants

A series of new, kinetically stable, crystalline superlattice compounds containing integral number of intergrown dichalcogenide layers were prepared through controlled crystallization of Ti/Se/Nb/Se superlattice reactants with designed compositional modulation. Discussed in this paper is a family of structural isomers with the overall stoichiometry of NbTiSe4. Specifically, the members of this series containing 1/1, 2/2, 3/3, 4/4, 6/6, 8/8, 9/9, 12/12, and 15/15 TiSe2/NbSe2 units as the unit cell of the superlattice were prepared as polycrystalline thin films oriented with the dichalcogenide layers perpendicular to the substrate surface. Low-angle diffraction data collected as a function of time and temperature reveal that the initial layered reactant contracts in the c-axis direction and that the interfaces become smoother during initial interdiffusion. Theta−theta scans show a gradual decrease of the (00l) diffraction line widths of the growing compound as a function of annealing time and temperature indicating an increase in the c-axis domain size. High-angle rocking curve diffraction data show increasing c-axis orientation, suggesting TiSe2/NbSe2 crystal growth perpendicular to the substrate surface upon low-temperature annealing. The end products of this synthetic approach are high quality c-axis-oriented TiSe2/NbSe2 crystalline superlattices with designed structure resulting from relatively low-temperature annealing at 500 °C. A working model for the formation of crystalline superlattices from the modulated reactants is presented which is consistent with the data.

The effects of diluent molecular weight on the structure of thermally-induced phase separation membrane

The effects of molecular weight of a homologous series of diluent on the droplet size of the thermally-induced phase separation membranes were investigated for the mixtures of poly(ethylene glycol) used as a diluent and nylon 12 as a matrix. All the phase diagrams obtained for different molecular weights of the diluent ranging from 200 to 600 showed the upper critical solution temperature type phase boundaries. When molecular weight of PEG was higher than 1000, nylon 12 did not form miscible blends with PEG below the thermal degradation temperature. Interaction energy denssty for each pair was evaluated from the phase separation temperature by the Flory-Huggins theory. The chain end group effects on the interaction energy were also considered using a binary interaction model and a Massa plot. The equilibrium domain size increased as the molecular weight of the diluent increased and then approached an asymptotic value. The increase of the average domain size with the increase of the diluent molecular weight was suppressed to a great extent for a higher content of nylon 12 in the mixture suggesting that there exist specific interactions between PEG and nylon 12.

A Highly Ordered Self-Assembled Monolayer Film of an Azobenzenealkanethiol on Au(111): Electrochemical Properties and Structural Characterization by Synchrotron in-Plane X-ray Diffraction, Atomic Force Microscopy, and Surface-Enhanced Raman Spectroscopy

The synthesis and characterization of p-HS(CH{sub 2}){sub 11}OC{sub 6}H{sub 4}N=NC{sub 6}H{sub 5}, compound 1d, is reported. Compound 1d self-assembles onto Au(111) substrates into highly ordered monolayer films. Self-assembled monolayer films (SAMs) of 1d on Au(111)/mica have been characterized by ellipsometry, surface-enhanced Raman spectroscopy (SERS), and atomic force microscopy (AFM). We also report the characterization of SAMs of 1d on bulk single crystal Au(111) by synchrotron in-plane X-ray diffraction (XRD) measurements. AFM and in-plane XRD suggest that a SAM of 1d is comprised of domains of 1d which form a hexagonal lattice (4.50 {+-} 0.06 A nearest neighbor spacing) that is incommensurate with the underlying Au(111) lattice. A model is proposed to describe the SAM structure. In such a model, small bundles (nearly 80 molecules) of ordered azobenzene moieties that rest over a set of inward tilting alkyl surface tethering groups make up the individual domains. Thermal annealing of the as-deposited SAM of 1d results in a modest increase in domain size from nearly 45 to around 55 A and a change in azobenzene tilt angle from 20-30{degree} to approximately 0{degree} with no change in nearest neighbor spacing. The redox activity of the azobenzene group is significantly affected by monolayer filmmore » structure. Only 2% of the azobenzene groups within a SAM of 1d are electrochemically accessible through cyclic voltammetry in a THF/0.1 M n-Bu{sub 4}NPF{sub 6} electrolyte. 46 refs., 13 figs.« less

The Preparation of Crystalline NbSe2/TiSe2 Superlattices from Modulated Elemental Reactants

ABSTRACTThree new crystalline NbSe2/TiSe2 superlattice compounds with 43.472±0.005A, 80.66±0.03A and 117.9±0.1Å unit cells in thec direction were prepared through controlled crystallization of Ti/Se/Nb/Se superlattice reactants with different compositional layer thicknesses. Theta-theta and rocking curve data were collected using a theta-theta diffractometer to study the evolution of the initially layered reactants into the crystalline superlattices as a function of temperature. Low angle diffraction data demonstrates that the initial layered reactant contracts in the c-axis direction upon initial annealing and suggests that the interfaces become smoother during this initial interdiffusion. High angle rocking curve diffraction data shows the development of caxis oriented NbSe2fTiSe2 crystal growth perpendicular to the substrate surface. Theta-theta scans show a gradual decrease of the (001) diffraction linewidths of the growing compound as a function of annealing time and temperature indicating an increase in the c-axis domain size. High quality caxis oriented TiSe2/NbSe2 crystalline superlattices result from annealing at the relatively low temperature of 500ºC. The rational synthesis of intergrowth compounds from superlattice reactants as described herein will permit the tailoring of physical properties as a function of compositional layer thicknesses and nativeproperties of the parent compounds.

Very low‐grade metamorphism of the Taveyanne greywacke, Glarus Alps, Switzerland

ABSTRACTDetailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic Eocene‐Oligocene Taveyanne greywacke of the Glarus Alps, Eastern Switzerland. Presented data indicate an increase of metamorphic grade from zeolite facies to prehnite‐pumpellyite and pumpellyite‐actinolite facies. Low‐grade outcrops contain laumontite, minor corrensite and pumpellyite (assemblage type 1), whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite (type 2), prehnite—pumpellyite‐(Al)—white mica (type 3), a single outcrop shows pumpellyite‐actinolite facies (type 4). From the zeolite to prehnite‐pumpellyite/pumpellyite‐actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain ≤1 mm) in type 1, to a few millimetres in type 2, and to a whole thin section in type 3. MetamorphicP‐Tconditions were determined by a combination of chlorite thermometry, fluid inclusion and vitrinite reflectance data. Peak temperatures range from 170‐190d̀ C for zeolite facies to 270‐310d̀ C for prehnite‐pumpellyite and pumpellyite‐actinolite facies. For the higher temperature range, pressures of 2‐3 kbar are derived indicating a geothermal gradient of 24‐32d̀ C km‐1. The well‐constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed. The best correspondence to the temperatures determined here is for the Cathelineau calibration. In addition, in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites.

Local atomic structural changes on structural relaxation in a Pd 82Si 18 amorphous alloy

The microstructural changes on low temperature annealing of amorphous Pd 82Si 18 ribbon specimens were observed using high-resolution electron microscopy and the results were correlated with the structural relaxation. At the initial stage of annealing up to 573 K, atomic medium-range order (MRO) develops and grows. At temperatures higher than 573 K but below the glass transition temperature, the MRO domains grow to f.c.c. nanocrystals which change the profile of the electron diffraction pattern, especially of the second halo ring. According to nano-beam elemental analysis on annealing using sputter-deposited Pd 82Si 18 thin films, the Si content in the MRO domains and nano-precipitates decreases as the domain or particle size increases. It is concluded that the atomic free volume introduced during amorphization is annihilated by atomic rearrangement in the formation and development of the MRO domains, and the chemical order must be developed in the dense random packing (DRP) matrix by the diffusion of Si from MRO into the matrix. The structural relaxation corresponds to these local atomic structural changes.

Micrograin structure influence on electrical characteristics of sputtered indium tin oxide films

The relationship between micrograin structures and electrical characteristics of sputtered indium tin oxide (ITO) films was investigated. Micrograin structures were observed by a high resolution scanning electron microscope. Electrical characteristics were evaluated by four point probe resistance measurement and Hall effect measurement. Low resistivity ITO films had domain structures. One domain consisted of many sputter grains having the same orientation. The resistivity decreased with increasing domain size. The domain boundary might cause scattering for conduction electrons. Therefore, larger domain ITO films had a higher Hall mobility. The minimum resistivity was 1.8×10−4 Ω cm, deposited at a sputtering voltage of −250 V and a 250 °C deposition temperature. The electron conduction mechanism in domain structured ITO films was taken into consideration.

A harmonic/anharmonic energy partition method for lattice statics computations

A method of lattice statics analysis is developed. Consideration of anharmonic effects is restricted to finite regions surrounding lattice defects. All displacements of the crystal are expressed as the effect of unknown forces applied to a perfect harmonic lattice of infinite extent. Displacements are related to the unknown applied forces by means of the Green function of the perfect harmonic lattice, so that equilibrating forces need only be applied to the anharmonic region. The unknown forces are determined so as to maximize the complementary energy of the crystal, which yields a lower bound to the potential energy. The method does not require the explicit enforcement of equilibrium or compatibility conditions across the boundary between the harmonic and anharmonic regions. The performance of the method is assessed on the basis of selected numerical examples. The rate of convergence of the method with increasing domain size is found to be cubic. This is one or two orders of magnitude faster than rigid boundary methods based on the harmonic and continuum solutions, respectively.

Rayleigh scattering in Sr0.61Ba0.39Nb2O6

Rayleigh scattering (λ=488 nm) is observed in single-crystal Sr0.61Ba0.39Nb2O6 (SBN:61). In particular, the scattered intensity is measured as a function of temperature across the ferroelectric–paraelectric phase transition. The results show that the scattered intensity can vary by as much as two orders of magnitude in passing through the transition. The particular form of the intensity-vs-temperature curve is found to depend on the poling history of the crystal. The unpoled crystal exhibits a rapid change from strong scattering below the transition (ferroelectric state) to weak scattering above the transition (paraelectric state). The measured inflection point is near 63 °C upon heating and near 58 °C upon cooling. In this case the scattering is predominantly attributed to the presence of high-density ferroelectric domains, which vanish above the transition. If the crystal is thermally poled (by cooling through the transition with an electric field applied), it shows no measurable domain scattering but does exhibit strong central-peak behavior at 65 °C upon heating and 59 °C upon cooling. Despite repeated cycling through the transition, the previously thermally poled crystal consistently displays central-peak behavior. The results suggest that thermal poling in SBN followed by thermal depoling produces a significant increase in the average ferroelectric domain size when compared to the unpoled crystal.

Chlorite crystallinity: an empirical approach and correlation with illite crystallinity, coal rank and mineral facies as exemplified by Palaeozoic and Mesozoic rocks of northeast Hungary

Abstract Fairly strong (r= 0.75–0.85) positive linear correlations were found between crystallinity indices (peak widths) measured on the first two basal reflections of chlorite and those of illite–muscovite in <2‐μm fractions of a representative shale–slate–phyllite series from Palaeozoic and Mesozoic formations of northeast Hungary. The metamorphic grade ranges from late or deep diagenesis through anchizone to epizone conditions. Chlorite crystallinity values measured on air‐dried and ethylene‐glycol‐solvated samples suggest that the effects of expandable interlayers are negligable, especially in the higher grade (∼temperature) part of the series. However, the greater scattering of crystallinity values for the chlorite 001 reflection compared to those of the 002 reflection may be related to the effects of minor amounts of interlayered and/or discrete smectite and/or vermiculite. With increasing metamorphic grade and advancing equilibrium recrystallization, the chlorite compositions in different samples become more homogenous. No correlation exists between crystallinity and changes in chlorite composition as estimated from the intensity ratios of basal reflections. Hence an increase of domain size and a decrease of lattice distortion with increasing grade (∼temperature) may be decisive factors affecting chlorite crystallinity.Chlorite crystallinity can be applied as a reliable regional, statistical technique complementary with, or instead of, the illite crystallinity method. The illite and chlorite crystallinity scales used here are related to Kübler's epi‐, anchi‐ and diagenetic zones and correlated with coal rank, conodont colour alteration and mineral facies data. As the effects of the detrital white mica can be observed even in the <2‐μm fractions of anchizonal metapelites, the anchizone boundaries determined solely on the base of ‘fixed’illite crystallinity values may vary with amounts of detrital and newly formed muscovite–illite. Hence a complex approach utilizing more than one method for determination of grade is preferred for petrogenetic purposes, even if relationships between crystallinity scales, coal rank and mineral facies also vary strongly in different tectonic settings and lithologies.

Effect of molybdenum substitution on B2 antiphase domain formation in rapidly solidified FeAlMo alloys

Studies at Sheffield have shown that the increase in B2 ordering temperature obtained with increase in aluminium content in rapidly solidified FeAlX (X = Cr, Mo) alloys results in an increase in B2 antiphase domain (APD) size. The present contribution concerns the effect of increasing molybdenum substitution for iron in such systems, which is shown to increase the ordering temperature but decrease the B2 APD size. The results are discussed in terms of the extension of solid solubility of molybdenum by rapid solidification, molybdenum segregation to the antiphase boundaries, and molybdenum diffusion in these alloys.

垂直磁気ヘッド主磁極膜の磁区構造制御法

The effect of domain structures of main-pole films on reproducing sensitivities were investigated for various single pole type perpendicular magnetic heads. The reproducing sensitivity of the heads made of a Co-Zr-Nb single layer becomes unstable and decreases with the increase of closure domain size when the track width narrows and the anisotropy field Hk decreases. On the other hand, when the wall of closure domains can be pinned by grooving at the only edge of a main-pole film, the magnetization rotates without any disturbance in main domains. Using this novel domain control method, closure domains become smaller even for smaller Hk, an d a stable and highly sensitive single-pole head can be obtained.