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Purpose: In recent years, natural dyes have attracted significant attention globally because of growing public awareness of the environment and health hazards associated with synthetic dyes. Natural dyes can provide special aesthetic qualities as well as the ethical significance of a product which is environmentally friendly. By keeping this burning issue in mind, this study aims to explore the dyeing properties of various unexplored environmentally friendly natural dyes. Design/methodology/approach: In this study, the aqueous extract of coconut leaves is used for dyeing purpose. The silk and jute fabrics were dyed with the extract alone as well as in combination with metal salts as mordants by employing pre-, meta- and postmordanting techniques. The dyeing properties of the colored samples were evaluated by measuring their color strength; CIEL*a*b* values; and color fastness to washing, light and rubbing. Findings: A yellow shade was achieved when the fabric samples were dyed solely with the extract. However, shade variations were observed when different mordants and mordanting techniques were applied. In all the cases, metallic salts improved the color fastness properties of dyed samples to washing, light and rubbing especially for the silk fabric. Originality/value: To the best of the authors' knowledge, this is the first report on a natural dye extracted from the leaves of coconut. Leaf as the source of dye has added an extra advantage, as it is reproducible and can be collected easily without harming the plants. The reported dye could be an attractive choice for sustainable and eco-friendly dyeing. [ABSTRACT FROM AUTHOR]

Palladium nanoparticles on ethylenediamine-grafted functionalized chromium-based metal organic framework (Pd-ED-MIL-101) was tested for the hydrogenation of styrene oxide to 2-phenylethanol, the key ingredient of the rose essence. The catalyst was found as an excellent heterogeneous recyclable catalyst for selective hydrogenation of styrene oxide to 2-phenylethanol (100% conversion and ∼100% selectivity) within 2 h in methanol with a catalyst loading only 0.25 mol % palladium at ambient pressure and temperature under molecular hydrogen. If the catalyst loading increases to 0.50 mol % palladium, the conversion time reduces to 1 h. In repeated runs (tested for 5 cycles) showed no loss of activity and selectivity of the catalyst. To the best of our knowledge, the performance of the present catalyst is one of the best compared to all other reported catalysts in terms of conversion, selectivity, reaction time, reaction conditions, purification, catalyst stability, catalyst loading, catalyst recyclability, safety and convenience. [ABSTRACT FROM AUTHOR]

Background: Tinggong is an indigenous rice variety in Aceh Province known for its excellent cooking quality and tolerance to adverse climatic conditions such as drought. However, this local rice has a long lifespan ranging from 150-160 days and is susceptible to Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial leaf blight (BLB). Methods: To improve the performance of Tinggong, the variety was cross-breed with the isogenic line IRBB27 which confers Xa-27 and sd-1 genes. The inheritance of both of these genes and the changes in their agronomic character and the resistance to Xoo were analyzed in the F3 progenies to identify the presence of both Xa-27 and sd-1 genes in the F3 progenies and the implication of their phenotypic characters. Result: The results showed that 58.33% of progenies inherited both Xa-27 and sd-1 genes. Of these, 4 progenies consisting #T5, T6, T29 and T30 are the potential to develop as they show both genotypic and phenotypic improvement. The 4 progenies produce earlier (116-120 days after sowing) with plant height 109-128 cm and more resistance to Xoo (lesion length 2.08-2.42 cm), the weight of grains per hill reached 26.24-34.12 g or yield potential (10.40-43.55%) higher compared to their parent Tinggong. [ABSTRACT FROM AUTHOR]

In this study, the influence of hydrothermal reaction temperatures on V2O5synthesized via a green facile mild hydrothermal method at six different reaction temperatures ranging from 100 to 200 °C, at steps of 20 °C and the physical properties the synthesized samples have been investigated. The x-ray diffraction pattern confirms the stable orthorhombic crystal structure of the synthesized samples at all reaction temperatures. The scanning electron microscopy and transmission electron microscopy images demonstrate the particle-like morphology, and these characterizations affirmed that the particles' size became larger with the increase in the reaction temperatures. To study the functional groups, Fourier-transform infrared investigation has been employed. The bandgap of the synthesized samples has been estimated using UV-vis diffuse reflectance spectra and was found to vary from 2.08 to 2.15 eV, which implies their suitability for absorbing a significant amount of visible light. The photocatalysis of methylene blue with synthesized samples has been carried out to investigate the photocatalytic efficiency. Pure V2O5 synthesized at a lower reaction temperature (100 °C) possesses a lower bandgap and, accordingly, higher photocatalytic efficiency. [ABSTRACT FROM AUTHOR]

There has been recently a worldwide interest in the production and application of natural dyes due to the growing awareness about cleaner surroundings and healthy lifestyle. The new sources of natural dyes increase the scope of textile dying with eco-friendly dyes and able to alleviate the adverse effects in this sector. Reported here is a new natural dye that was extracted from the leaves of date palm using simple aqueous extraction process. The natural dye extract obtained from date leaves was used in dyeing of cotton and silk fabrics with different mordants by applying different mordanting techniques and the properties of the dyed fabrics were evaluated by their color strengths and fastness properties. A reddish shade was observed when used the dye extract only; however, a variety of shades were achieved when different mordants and mordanting technique were used. In most of the cases, impressive color strengths and fastness properties were observed for dyed fabrics. These results are very attractive from a practical point of view for eco-friendly dying. [ABSTRACT FROM AUTHOR]

The objective of this study is to probe the effects of boundary layer flow over an exponentially stretching cylinder having nonlinear velocity placed in a porous medium. The modeled partial differential equations are transformed into nonlinear ordinary differential equations by applying suitable similarity transformations. A numerical solution is attained using the finite difference Keller–Box method. The physical parameters and skin friction coefficients are studied on the velocity profile. The fluid velocity and skin friction coefficient decrease with the increase in Re and κ, while a reverse behavior is reported for ɛ. [ABSTRACT FROM AUTHOR]

The excessive energy utilisation worldwide has prompted awareness of finding a new clean energy. Malaysia has large oil palm resources and releases huge amounts of oil palm biomass. Since oil palm biomass is abundantly available in Malaysia, it has the high potential of being utilised as fuel for gasification technology. Although many institutions in Malaysia are undertaking numerous research activities, the gasification technologies are not progressing as expected. The understanding of the potential and challenges faced by Malaysian industries are vital to evaluate the feasibility of gasification technology using oil palm biomass in Malaysia. [ABSTRACT FROM AUTHOR]

A novel hybrid polyester composite comprising jack tree and jute fibers reinforced with eggshell filler is presented addressing the global need for sustainable alternatives to synthetic materials. The comprehensive analysis of physical and mechanical properties, such as tensile strength, impact resistance, hardness, water uptake was carried out using Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). The manual hand layup technique was employed to ensure reproducible composite production. The resulting materials exhibited favorable mechanical properties, with the tensile strength and elongation balanced between jute and jack tree fibers, augmented by the reinforcing effect of the eggshell filler. Jack tree fibers significantly enhanced impact strength, contributing to the overall toughness of the composite. Hardness testing revealed higher crystallinity attributed to jack tree fibers. Water absorption characteristics demonstrated a nuanced interaction between cellulose abundance and fiber mass. FTIR spectroscopy provided molecular insights, while SEM analysis visually depicted the intricate structure of the composite. The amalgamation of jack tree and jute fibers with an eggshell filler not only enhances mechanical prowess but also aligns with global environmental efforts. This research advances sustainable composite materials, offering nuanced insights into the interplay between natural fibers, fillers, and matrices, with implications for eco-friendly solutions in diverse industries. The findings contribute to a greener, more sustainable future in industrial applications. [ABSTRACT FROM AUTHOR]

For a skyrmion lattice phase of chiral magnets, we compare predictions of the Landau-Lifshitz-Gilbert (LLG) and Thiele equations for the current-induced drift velocity for a given constant spin velocity. Instead of integrating the equations over a unit cell, we only perform an angle average, while retaining information on the radial dependence of velocity within the skyrmion. Since the skyrmion-lattice dynamics draws from magnetostatic, chiral, and exchange forces, we find that different scales are involved for the m=-1 and m=-2 skyrmions, a fact that might be useful in "tuning" scales of the drift velocity. We note that the Thiele equation yields less information than the LLG equation and explain why the translation mode has not yet been observed. [ABSTRACT FROM AUTHOR]

Temu Glenyeh (Curcuma soloensis Val.) belongs to the family Zingiberaceae. Although it is synonymous with Curcuma longa L., the two are different species. Given that the morphological characters of this herb overlap with those of other Curcuma species, distinguishing these species on the basis of morphological criteria is difficult. The aim of this study was to determine the genetic variation and relationship of C. soloensis Val. on the basis of molecular characters by using intersimple sequence repeats (ISSRs). The samples consisted of 32 accessions and were obtained from 12 districts in Java Island. Ten ISSR primers were used in amplification. Molecular data were analyzed numerically in the form of binary data. The similarity indexes were obtained on the basis of the Jaccard coefficient by using the UPGMA method. Cluster and principal component analyses (PCA) were performed with the MVSP 3.1 program and UPGMA method. This investigation revealed that the 10 ISSR primers provided 37 ISSR bands comprising 28 polymorphic and nine monomorphic bands. Cluster analysis yielded two large groups, namely A (Curcuma zanthorrizha Roxb.) and B (C. soloensis Val. and Cucurma longa L.) with a coefficient of 0.566. C. zanthorrizha Roxb. (Temulawak) and C. longa L. (turmeric) belonged to the same genus as C. soloensis Val. The 0.70 phenon line showed that two accessions of C. longa L. (CL-1 and CL-3) clumped with all other accessions of C. soloensis Val. from Java. The PCA findings indicated that the characters that played the most prominent role in managing the grouping of C. soloensis Val. accessions were the primers SPS3 (515 and 425 bp), HB12 (207 bp), HB14 (351 bp), P3 (1083 and 651 bp), 811 (345), 817 (502 and 402 bp), and 824 (371 bp). [ABSTRACT FROM AUTHOR]

A new 4D memristive chaotic system with an infinite number of equilibria is proposed via exhaustive computer search. Interestingly, such a new memristive system has a plane of equilibria and two other lines of equilibria. Lyapunov exponent and bifurcation analysis show that this system has chaotic solutions with coexisting attractors. The basins of attraction of the coexisting attractors show chaos, stable fixed-points, and unbounded solutions. Furthermore, the 2D parameter space of the system is explored to find the optimum values of the parameters using the ALO (Ant Lion Optimizer) optimization algorithm. [ABSTRACT FROM AUTHOR]

The present study is about the numerical analysis of Casson fluid's boundary layer slip flow beneath the impact of suction/blowing past a permeable cylinder stretching exponentially. The modeled partial differential equations are transformed to nonlinear ordinary differential equations by applying the appropriate nonlinear transformation. The Keller box procedure, a tool famous for its numerical achievements, is used. The impact of relevant physical parameters like suction, Casson fluid, and Reynolds number and slip parameters on temperature and velocity distribution is studied and shown through graphs. The change in physical quantities like the Nusselt number and the skin friction coefficient with respect to variation of the parameters mentioned earlier was also examined. Their values are given in the form of a table. To ensure authenticity of the numerical procedure, outcomes of the present investigations are compared with previous works, and strong agreement is noticed. [ABSTRACT FROM AUTHOR]

In recent years, studies related to the epoxidation of fatty acids have garnered much interest due to the rising demand for eco-friendly epoxides derived from vegetable oils. From the epoxidation reaction, there is a side reaction involving epoxide and water. This reaction produces a by-product – dihydroxystearic acid (C18H36O4, DHSA). DHSA is one of the chemical precursors in the production of cosmetic products. Therefore, a kinetic model was developed to determine the optimised epoxidation process and concentration of DHSA, where each of the reactions was identified. The kinetic rate, k parameters obtained were: k11 = 6.6442, k12 = 11.0185, k21 = 0.1026 for epoxidation palm oleic acid, and k41 = 0.0021, k51 = 0.0142 in degradation process. The minimum error of the simulation was 0.0937. In addition, DHSA yield optimisation was done through Taguchi method, and the optimum conditions obtained were H2O2/oleic acid – OA unsaturation molar ratio 1 : 1 (level 2), formic acid – FA/OA unsaturation molar ratio 0.5 : 1 (level 1), temperature 35 °C (level 1), and agitation speed 100 rpm (level 1). A high yield of DHSA can be achieved under these conditions. [ABSTRACT FROM AUTHOR]

We propose a magnetic random access memory (MRAM) device in which both the writing and reading processes are realized within a single ferromagnetic (FM) layer. The FM layer is sandwiched between layers of heavy element and oxide to enhance the Rashba spin-orbit coupling (RSOC). When the in-plane FM moments are oriented at some intermediate angle to the current direction, the RSOC effect induces a spin accumulation in the FM layer, which in turn generates a Rashba spin torque field via the s-d exchange interaction. This field acts as the writing field of the memory device. The RSOC also induces a charge accumulation in the transverse direction via the inverse spin Hall effect (ISHE), which can be used to realize the memory read-out. The writing and read-out processes of the proposed memory are modeled numerically via the non-equilibrium Green's function technique. Besides the advantages of Rashba spin torque writing, i.e., no spin injection and symmetrical data-writing process, this single FM layer MRAM design does away with having a giant magnetoresistive or magnetic tunnel junction multilayer structure by utilizing the ISHE for the read-out process. [ABSTRACT FROM AUTHOR]

We study Klein tunneling across a PN junction in monolayer graphene (MLG) and the AB-bilayer graphene (BLG) under the effect of a perpendicular magnetic-field (B-field). In the Klein tunneling process, normally incident electrons in MLG (BLG) are fully transmissive (reflective) upon hitting the junction barrier. When a finite B-field is applied, transmission of the normally incident electrons is suppressed in MLG over an energy range around the PN barrier height, effectively opening an energy gap. This suppression may be attributed to the magnetic deflection arising from Lorentz force, which shifts the transmission profile of the device in the transverse direction. [ABSTRACT FROM AUTHOR]

The axion coupling in topological insulators (TI), which couples electric polarization (magnetization) with the magnetic (electric) field, is known to support a small-distance Casimir repulsion and a large-distance Casimir attraction with a zero-force stable equilibrium between TI plates. By enhancing the reflection properties of the TI interface through mirrors that introduce multiple reflections, we show that it is possible to maintain these trends while tuning the position of the zero-force point and its binding energy: the former by an order of magnitude and latter by over four orders. Moreover, surface charge on the TI allows for intermediate tuning of the zero-force point between coarse settings determined by the axion coupling. [ABSTRACT FROM AUTHOR]

In 2009, T. Mansour, M. Schork, introduce the concept of bridge graphs. A bridge graph B(G1, G2, ... , Gm) = B(G1, G2, ... , Gm; v1, v2, ... , vm) of with respect to the vertices is the graph obtained from the graphs G1; G2; ... ; Gm by connecting the vertices vi and vi+1 by an edge for all I = 1; 2; ... ; m-1. In this paper, we determine hyper-Zagreb index, first multiple Zagreb index, second multiple Zagreb index, Zagreb polynomials and M-polynomial for nano structures of bridge graphs. [ABSTRACT FROM AUTHOR]

Graph theory is vital for modeling and designing any chemical structure or network. Chemical graph theory is helpful to under first and about the structural characteristics of a molecular graph. The molecular graph is a graph in which vertices represent atoms and edges represent the chemical bond between atoms. Among topological descriptors, connectivity invariants are very beneficial and they have a useful part in chemistry. In this article, we study the chemical graphs of carbon graphite and we compute and derive close formulas of eccentricity based topological indices, such as eccentric based first Zagreb index, eccentric based second Zagreb index and eccentric based third Zagreb index of carbon graphite CG(m; n) for 3-layer. [ABSTRACT FROM AUTHOR]

By utilizing the degree of the vertex of the graphs, M-polynomials of book graph obtained and examined in this paper. The various vertex degree dependent indices of book graph can be calculated readily by using the proposed M-Polynomials of the book graph. We also give graphical representation of the calculated topological indices. [ABSTRACT FROM AUTHOR]

For a graph G the duplication operation of a vertex vbya new edge e = uw results in a new graph G'such thatN (u) -- (v, w) and N (w) -- {v, u). The duplication operation of an edge e = uv by a new vertex w results in a new graph G" such that N (w) = {u, v). In this article we have discussed that the properties of a graph, with minimum degree 2 of any vertex, to be super vertex-antimagic total and to be super edge-antimagic total are invariant under the above duplication operations. Also, we have discussed on the existence of the so-called k super vertex-antimagic total vertex modifications and k super edge-antimagic total edge modifications for graphs. [ABSTRACT FROM AUTHOR]

A chemical compound can be represented as a chemical graph. A topological index of a (chemical) graph is a numeric value of a graph which characterize its topology and is usually graph invariant. The Zagreb indices, Randic index and sum-connectivity indices are useful in the study of antiinflammatory activities, boiling point, molecular complexity heterosystems of certain chemical instances, and in elsewhere. In this paper, we calculate the mentioned topological indices of some infinite classes of prophyrin dendrimers. [ABSTRACT FROM AUTHOR]

In this paper a new 5D chaotic system with line equilibrium is designed and described to reveal its extreme multi-stability. Hence, all of the resulting attractors are hidden. The suggested system owns many complex dynamic behaviors in comparison with other chaotic systems. System initial state-associated complex dynamical behaviors are considered and we discover that it possesses an immeasurable number of coexisting attractors, which expresses the occurrence of extreme multi-stability. Besides, we also demonstrate the line equilibrium stability in detail, bifurcation diagrams, Lyapunov exponents, and basins of attraction. Also, in order to analyze the new 5D chaotic system we have considered the permutation entropy technique. Finally, the application of the novel 5D chaotic system with line equilibrium to the problem of chaos synchronization and secure communication through observer design is presented. [ABSTRACT FROM AUTHOR]

Although chaotic flows with special properties in their equilibria have been investigated widely, such an effort about chaotic maps has been neglected. In this note, we introduce a dynamical map with an infinite number of equilibrium points. Such a system doesn't exist in the literature. A complete dynamical analysis is done on this new map which reveals its rich potential in showing chaos and multi-stability. [ABSTRACT FROM AUTHOR]

In this paper, we introduce an interesting new megastable oscillator with infinite coexisting hidden and self-excited attractors (generated by stable fixed points and unstable ones), which are fixed points and limit cycles stable states. Additionally, by adding a temporally periodic forcing term, we design a new two-dimensional non-autonomous chaotic system with an infinite number of coexisting strange attractors, limit cycles, and torus. The computation of the Hamiltonian energy shows that it depends on all variables of the megastable system and, therefore, enough energy is critical to keep continuous oscillating behaviors. PSpice based simulations are conducted and henceforth validate the mathematical model. [ABSTRACT FROM AUTHOR]

Multistability is an essential topic in nonlinear dynamics. Recently, two critical subsets of multistable systems have been introduced: systems with extreme multistability and systems with megastability. In this paper, based on a newly introduced megastable system, a megastable forced oscillator is introduced. The effect of adding a forcing term and its parameters on the dynamical behavior of the designed system is investigated. By the help of bifurcation diagram and Lyapunov exponents, it is shown that the modified oscillator can show a variety of dynamical solutions including limit cycle, torus, and strange attractor. [ABSTRACT FROM AUTHOR]

A heterogeneous palladium(II) catalyst anchored to modified metal-organic framework has been synthesized and characterized. The performance of the catalyst has been tested for the hydrogenation of styrene oxide at ambient temperature and pressure. The catalyst showed an excellent activity and selectivity for the preparation of 2-phenylethanol from styrene oxide with 100% conversion and 98% selectivity. The catalyst is very stable and easily recyclable for several times without loss of activity. [ABSTRACT FROM AUTHOR]

Multi-layer networks are quite fundamental to study structural and functional properties of various biological systems. In this study, a two-layer neuronal network is considered and the interactions between the spiral pattern in one layer and a homogeneous state in the other layer, under the effect of inter-layer bidirectional connection are investigated. Spiral wave has been confirmed to play a significant role in many complex systems. In this regard, in laminar structured systems in particular, it is crucial to study the dynamics of the spiral wave affected by the inter-layer interactions. Here, for each layer (sub-network), a regular network with eight-neighbor connection is designed. For the local dynamics of each neuron, the magnetic Fitzhugh–Nagumo (FN) neuronal model is introduced. The results show that depending on the level of interactions between the two layers, four different types of collective electrical activity can occur. When the inter-layer connection is weak, the layer with spiral pattern does not change while the homogeneous state of the other layer is broken by a blurred spiral pattern. As the inter-layer connection is strengthened, the dynamics of the spiral wave changes significantly, leading to unstable spiral wave and spiral turbulence. However, by a further increase in the inter-layer coupling strength, the spiral wave does not exist at all. [ABSTRACT FROM AUTHOR]

A new 4-D memristive chaotic flow is proposed in this paper. Dynamical investigation of the proposed system shows some specific properties. The system has a line of equilibria which are unstable in some limited intervals and stable at other intervals. Investigating bifurcation diagram of the system shows an inverse period-doubling route to chaos. Also, different initiation in plotting bifurcation diagram shows its multistability. In some intervals of the parameter, two Lyapunov exponents of the system are positive, and the attractor is hyper-chaotic. However, in some other ranges of parameters, only one Lyapunov exponent is positive, and the attractor is chaotic. Basin of attraction of the system is studied which shows a vast region of attraction for the chaotic attractor. Entropy analysis of the system provides a viewpoint into the unpredictability of the system. [ABSTRACT FROM AUTHOR]

The counterpropagating edge states of a two-dimensional topological insulator (TI) carry electrons of opposite spins. We investigate the transport properties of edge states in a two-dimensional TI which is contacted to ferromagnetic leads. The application of a side-gate voltage induces a constriction or quantum point contact (QPC) which couples the two edge channels. The transport properties of the system are calculated via the Keldysh nonequilibrium Green's function method. We found that inter-edge spin-flip coupling can significantly enhance (suppress) the charge current when the magnetization of the leads are anti-parallel (parallel) to one another. On the other hand, spin-conserving inter-edge coupling generally reduces the current by backscattering regardless of the magnetization configuration. The charge current and the conductance as a function of the bias voltage, also exhibit similar trends with respect to spin-flip coupling strength, for both parallel and anti-parallel configurations. Hence, gate voltage modulation of edge states via a QPC can provide a means of modulating the spin or charge current flow in TI-based spintronics devices. [ABSTRACT FROM AUTHOR]

We present an overview of gauge fields in spintronics, focusing on their origin and physical consequences. Important topics, such as the Berry gauge field associated with adiabatic quantum evolution as well as gauge fields arising from other non-adiabatic considerations, are discussed. We examine the appearance and effects of gauge fields across three spaces, namely real-space, momentum-space, and time, taking on a largely semiclassical approach. We seize the opportunity to study other 'spin-like' systems, including graphene, topological insulators, magnonics, and photonics, which emphasize the ubiquity and importance of gauge fields. We aim to provide an intuitive and pedagogical insight into the role played by gauge fields in spin transport. [ABSTRACT FROM AUTHOR]

The insertion of a tunnel barrier between a ferromagnetic (FM) metal source lead and a semiconductor (SC) layer has proved effective in achieving high spin injection efficiency at the FM-SC interface. We investigate the spin transport across a FM-I (insulator)-SC interface, under the influence of a Schottky barrier which arises in the SC layer close to the interface. The spin transport in the presence of an applied voltage is calculated via the nonequilibrium Green’s function (NEGF) tight binding model. The NEGF formalism systematically accounts for: (i) the spatial profile of the Schottky barrier, (ii) the coupling between the FM lead and the SC layer, and (iii) the effect of the entire semi-infinite lead, which can be reduced to a self-energy term. We investigate several parameters (e.g., doping concentration, built-in potential and applied bias) which affect the Schottky barrier profile, and hence the spin current across the FM/I/SC system. It is shown that the spin polarization of current can be significantly improved by having a low Schottky barrier height, but a high built-in potential. A high doping density increases the current density by decreasing the Schottky barrier height and the depletion width, but at the cost of reduced spin polarization. [ABSTRACT FROM AUTHOR]

The electronic properties of armchair graphene nanoribbons (AGNRs) can be significantly modified from semiconducting to metallic states by applying a uniform perpendicular magnetic field (B-field). Here, we theoretically study the band gap modulation induced by a perpendicular B-field. The applied B-field causes the lowest conduction subband and the topmost valence subband to move closer to one another to form the n=0 Landau level. We exploit this effect to realize a device relevant magnetoresistive (MR) modulation. Unlike in conventional spin-valves, this intrinsic MR effect is realized without the use of any ferromagnetic leads. The AGNRs with number of dimers, Na=3p+1[p=1,2,3,...] show the most promising behavior for MR applications with large conductance modulation, and hence, high MR ratio at the optimal source-drain bias. However, the MR is suppressed at higher temperature due to the spread of the Fermi function distribution. We also investigate the importance of the source-drain bias in optimizing the MR. Lastly, we show that edge roughness of AGNRs has the unexpected effect of improving the magnetic sensitivity of the device and thus increasing the MR ratio. [ABSTRACT FROM AUTHOR]

We theoretically study the spin dependent transport through a magnetic double tunnel junction system, which consists of a nonmagnetic metal island sandwiched by two ferromagnetic electrodes. The transport model in both cotunneling and sequential tunneling regimes is based on the master equation, and systematically incorporates the effects of both intraisland spin-flip (SF) and SF during tunneling between the electrode and the island. We found that the tunnel magnetoresistance (TMR) in the cotunneling regime is impervious to either the intraisland SF or the tunneling SF effect. On the other hand, in the sequential tunneling regime, the TMR decreases with the increasing intraisland SF rate Γ and tunneling SF probability η (η<0.5). However, when the tunneling SF is much stronger, i.e., η>0.5, the TMR is enhanced by increasing the tunneling SF probability. The increase in the temperature suppresses the cotunneling TMR, whereas the sequential tunneling TMR is found to be more robust to temperature variation. [ABSTRACT FROM AUTHOR]

Sequential transport through a semiconductor quantum dot (QD) weakly coupled to two collinear magnetic leads is analyzed theoretically based on the master equation method. The transport model considers two discrete energy levels in the dot, i.e., the lowest unoccupied εe (electron) and the highest occupied εh (hole) energy levels, with associated Coulomb correlation energies Ue and Uh, respectively, and the spin-flip effect within the dot. The charge and spin currents and the tunneling magnetoresistance are evaluated in the sequential tunneling regime. It was found that when both energy levels, εe and εh, contribute to the tunneling transport, there is enhancement of the current as well as tunneling magnetoresistance, compared to the case of a single-level QD transport considered previously. The tunneling transport through the two levels of the QD also results in additional bias-dependence: it was observed that spin accumulation and magnetoresistance of the system are particularly suppressed by spin flip within the bias range corresponding to single QD occupancy. [ABSTRACT FROM AUTHOR]

A theoretical model is proposed to analyze both bulk and interfacial spin depolarization effects on the magnetoresistance (MR) of nanoscale spin valves (SVs). The model is based on the spin coupled Boltzmann transport equations where the momentum spin relaxation arising from spin flip and non-spin-flip scattering are considered. In the boundary conditions we include the parameter q which denotes the interfacial spin flip probability, while bulk spin depolarization is characterized by the ratio r of spin flip to non-spin-flip scattering times. We consider a typical Fe/Cr/Fe pseudo-SV trilayer, and calculate the current for parallel and antiparallel alignments, to deduce the MR. A decreasing trend in MR is observed with an increase in either r or q, with the dependence on q being more pronounced. We also studied the combined effect of interfacial diffusive scattering (described by parameters Ns and D↑) and spin flip scattering. We found that although diffusive scattering generally results in an improvement in MR, this is more than offset by the MR suppression effect arising from spin flip scattering. [ABSTRACT FROM AUTHOR]

We present a numerical simulation of current-induced magnetization switching (CIMS) in pseudospin-valve (PSV) structures exhibiting perpendicular anisotropy. The PSV structures consist of a reference layer of Co/Pt and Co/Ni multilayers and a free layer composed of Co/Ni multilayers. The spin torque induced by the passage of a spin-polarized current is modeled by means of a modified Landau–Lifshitz–Gilbert equation, which incorporates two additional spin-torque terms. Numerical micromagnetic simulations of the magnetization switching process predict a critical current density of the order of 107 A/cm2, a value consistent with available experimental results. In addition, we investigate the influence of the current sweep rate and the ratio of the in-plane and out-of-plane torque coefficients on the stability of the magnetization switching process. Our analysis provides a useful guide for optimal utilization of the CIMS effect in perpendicularly magnetized multilayers, for use in prospective spintronic applications. [ABSTRACT FROM AUTHOR]

We investigate the spin transfer torque arising from a perpendicular-to-plane current in a ferromagnetic (FM)-nonmagnetic-FM trilayer. Our analysis is based on the spin drift-diffusion model, modified for the case of noncollinear magnetization, i.e., with arbitrary angle θ between the magnetization orientation of the two FM layers. By solving the electrochemical potential and spin accumulation across the trilayer, we obtain the θ dependence of the magnetoresistance and spin transfer torque in the free FM layer. The optimal magnetization orientation θmax and the corresponding maximum torque τmax are investigated as a function of the FM layer thicknesses. Based on the analysis, we propose that (i) the free (fixed) FM layer thickness be set at approximately the transverse (longitudinal) spin relaxation lengths, and (ii) the relative FM orientation be biased at some intermediate angles instead of the conventional collinear configuration, in order to maximize the current-induced magnetization switching effect. [ABSTRACT FROM AUTHOR]

We represent the spin-dependent transport across a pseudospin-valve structure as described by the spin drift-diffusion (SDD) theory by an effective two-current model, in which the spin relaxation effects are globally absorbed into the two effective branch resistances. Our approach has eliminated the need for “spin flip” resistances interconnecting the two spin branches, which have the disadvantage of artificially localizing the effects of spin relaxation to arbitrary spatial points. We confirm the accuracy of our effective two-current model with the full numerical SDD solution. Based on our model, we found that (i) the overall magnetoresistance (MR) is much more sensitive to the spin relaxation effect in the nonmagnetic (NM) layer, compared to that in the ferromagnetic (FM) layers, and that (ii) the effective spin relaxation length λE in the NM layer is intrinsically linked to the conductivity σN,F of the NM and FM layers. We found that λE=λN/(η)1/2, where λN is the nominal spin relaxation length in the NM layer and η=(σN/σF). The analytical link between spin relaxation and conductivity explains the previously described anomalous suppression of MR, when the conductivity ratio η exceeds a certain critical value ηC. [ABSTRACT FROM AUTHOR]

We performed a theoretical study and analysis of the effect of modifying the layer thicknesses of a current-perpendicular-to-plane (CPP) spin valve multilayer on its magnetoresistance (MR) ratio. An increase in the ferromagnetic (FM) layer thickness results in (i) an increase in the spin-dependent component of its total resistance, thereby resulting in higher MR, but also leads to (ii) greater spin relaxation in that layer and (iii) an anomalous MR effect in the high resistance regime, both of which suppress the MR ratio. The interplay of these effects results in a complex MR dependence on FM thickness, instead of the simple monotonic MR increase predicted by the two-current model. It also explains the existence of an optimum FM thickness for maximum MR ratio, as evidenced by experimental data. Finally, we consider the MR dependence on the strength and spin selectivity of interfacial resistances, which can either arise naturally or be engineered in the spin valve structure. The study of the combined effects of the FM layer thickness and resistivity, the MR suppression in the high resistive limit, and the competitive spin-dependent scattering in the bulk and at the interfaces is essential for optimizing the structure and material of a practical CPP spin valve to achieve the maximum MR ratio. [ABSTRACT FROM AUTHOR]

We propose a ballistic, coherent transmission system that utilizes the magnetic and electric barriers as Boolean input variables to realize functions similar in principle to the conventional logic gates. For practical implementation of these functions, we propose to use a device construct based on the high-electron-mobility transistor (HEMT) with ferromagnetic (FM) and nonmagnetic (NM) metal gates deposited on top of the HEMT heterostructure. This device system can be manipulated to realize multiple logic functions such as OR, AND, and their inverse by applying different magnetic and electric field configurations on the FM and the NM gates. The charge transport simulation is based on the single particle effective mass Hamiltonian and ballistic charge transport. The calculation results demonstrate clear binary outputs corresponding to various logic functions, with “high” (“low”) state having transmission probability of T>90% (T<10%). [ABSTRACT FROM AUTHOR]

We present a micromagnetic model which incorporates eddy current and spin transfer torque effects due to the passage of a spin-polarized current in the current-perpendicular-to-plane (CPP) geometry. Eddy current effects are modeled by solving Faraday’s and Poisson’s equations self-consistently with the Landau-Lifshitz-Gilbert (LLG) equation, whereas spin transfer torque is modeled by including the Slonczewski spin torque term in the LLG equation. We consider a 50 nm cubic Co element, which forms the free layer of a pseudo-spin-valve structure. With a typical damping parameter of α=0.5, the eddy currents act to accelerate the magnetic reversal process. The spin torque effect can also assist the reversal process but at high current densities exceeding Jext=108 A/cm2 onwards. At these current densities, spin transfer torque also causes a substantial reduction in the coercivity. [ABSTRACT FROM AUTHOR]

We present a drift-diffusion transport model to evaluate the spin-injection efficiency η and magnetoresistance (MR) ratio in a ferromagnetic (FM) metal-semiconductor (SC)-FM metal trilayer structure. This model takes into account the differential interfacial resistances (IR) for spin-up and spin-down electrons and spin relaxation within the SC layer. The electrochemical potential μ for both spin directions is analytically solved and expressions for η, spin polarization of current P, and the MR ratio are derived. The presence of IR at the FM-SC boundary is crucial for generating a large spin splitting of μ, and consequently a high injection efficiency η. The IR needs to fulfill the requirements of (i) of a large magnitude comparable to the resistance of the SC layer and (ii) high asymmetry with respect to the two spin directions. To increase η from 1% to 30%, we require a large IR of 10-5 Ω cm2 and a spin asymmetry of 10:1. There are more stringent requirements for achieving a high MR ratio. An IR of 10-5 Ω cm2 and FM contact polarization Pc of 80% will only yield an MR ratio of 10%. We require a much larger IR ⩾10-4 Ω cm2 or virtually half-metallic contacts, i.e., Pc of ∼100% to achieve high MR ratio exceeding 50%. [ABSTRACT FROM AUTHOR]

We calculate, based on the effective mass Hamiltonian, the spin dependence of ballistic transport through a two-dimensional electron gas (2DEG) under the influence of an electric U and a pair of magnetic B barriers with finite spatial width. The spin polarization of electron transmission P is strongly dependent on the degree of asymmetry in the magnetic barriers. An asymmetry in the B barrier widths and heights which conserves the magnetic vector potential A along the conduction path leads to a low P of less than 1% in the high transmission region. If conservation of A is broken, much higher P values of up to 30% is achievable but at the cost of increasing the energy threshold Eth. Finally, we suggest a scheme which utilizes a thin break in the 2DEG conduction path to achieve a comparable modulation of P of 25%, while conserving A and maintaining Eth at moderate electron energies. [ABSTRACT FROM AUTHOR]

We present a model of tunneling magnetotransport across a ferromagnetic single electron transistor (FM-SET). The model applies the “orthodox” theory and the Master equation method to describe the stochastic nature of separate tunneling events. The coherent transport of an individual charge through a tunnel barrier is modeled by a free-electron Hamiltonian through a trapezoidal barrier, and a two-band model within the FM electrodes. Single electron charging effect is incorporated into both stochastic and coherent parts of the model. The calculated tunneling resistance R[sub t] is dependent on the thickness and voltage-dependent profile of the tunnel barriers. A bias modulation of the tunneling magnetoresistance (TMR) is obtained with the same period as the Coulomb staircase pattern. This modulation is present even for “homogeneous” FM-SETs, where each junction is of the same material composition. By contrast, previous studies based on the Julliere model predict total suppression of TMR modulation for such FM-SETs. The TMR modulation is found to be highly dependent on barrier thickness and the material composition of the junctions, implying further adjustable parameters for optimal TMR ratio. Finally, the bias modulation of TMR persists at high temperatures, even though the Coulomb staircase steps have been virtually smeared out. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which calculated the retention time of charges stored on a memory node of a multiple-tunnel junction (MTJ) memory device using a computationaly inexpensive approximation. Basic equations for MTJ; Cotunneling contribution of the current; Retention time in actual memory circuit; Conclusions.

This paper deals with a new modified hyperchaotic van der Pol–Duffing (MVPD) snap oscillator. Various dynamical properties of the proposed system are investigated with the help of Lyapunov exponents, stability analysis of the equilibrium points and bifurcation plots. The existence of the Hopf bifurcation is established by analyzing the corresponding characteristic equation. It is also proved that the MVPD oscillator shows multistability with coexisting attractors. Various numerical simulations are conducted and presented to show the dynamical behavior of the MVPD system. To show that the system is hardware realizable, we derive the discrete model of the MVPD system using the Euler's method and using the hardware–software cosimulation, the proposed MVPD system is implemented in Field Programmable Gate Arrays. It is shown that the output of the digital implementations of the MVPD systems matches the numerical analysis. [ABSTRACT FROM AUTHOR]

We analyze the topological Hall conductivity experienced by conduction electrons whose spins are strongly coupled to axially symmetric spin textures, such as magnetic vortex and skyrmion of types I and II, theoretically by gauge theory, and numerically via micromagnetic simulations. The numerical results are in agreement with the theoretical predictions. Divergence between the two is seen when the vortex/skyrmion core radius is comparable or larger than the element size, and when the skyrmion configuration breaks down at high Dzyaloshinskii-Moriya interaction strength. [ABSTRACT FROM AUTHOR]

We investigate the magneto-Coulomb (MC) effect in a ferromagnetic single electron tunneling transistor (FM-SETT), with asymmetric junction resistances and FM electrodes. The MC effect enables the conductance of the FM-SETT by an applied magnetic B-field in addition to the usual gate-bias modulation. Under optimal biasing of the asymmetric FM-SETT near the sawtooth edge of its gate oscillation, the sensitivity γB=dI/dB can be enhanced by a factor α, where α=R1/R2 denotes the junction resistance asymmetry. The enhanced B-field modulation is, however, susceptible to thermal smearing effects. Finally, an asymmetry in the magnetic properties of the FM leads results in a complex magnetoconductance response, with distinct conductance states. [ABSTRACT FROM AUTHOR]

We investigate the tunnel magnetoresistance (TMR) of the double barrier magnetic tunnel junction, where a quantum dot (QD) with discrete electron and hole energy levels is sandwiched between ferromagnetic leads. The effects of the symmetry of the coupling between the leads and the dot on both the TMR and spin accumulation (SA) are studied for voltage ranges corresponding to the QD’s single and double occupancies. When the QD is singly occupied, both the TMR and SA assume at their minimum values for symmetrical junctions with identical coupling strengths. For the doubly occupied QD, the opposite occurs with the highest TMR and SA being observed for symmetrical junctions with identical coupling strengths. The TMR is found to be strongly correlated with the spin accumulation in the QD. [ABSTRACT FROM AUTHOR]