Spin Behavior Research Articles

Laser-Assisted Melt Electrospinning of Poly(L-lactide-co-ɛ-caprolactone): Effect of Laser Power on Spinning Behavior and Fiber Structure Formation

Laser-Assisted Melt Electrospinning of Poly(L-lactide-co-ɛ-caprolactone): Effect of Laser Power on Spinning Behavior and Fiber Structure Formation

Numerical study of two-terminal SOT-MRAM

A fully three-dimensional model coupling charge, spin, magnetization, and temperature dynamics is employed to study the switching behavior of the two-terminal spin–orbit torque magnetoresistive random access memory (2T-SOT-MRAM). We demonstrated that free layer (FL) spin-transfer torque (STT) switching is strongly affected by the inclusion of the SOT. The nucleation of the FL magnetization reversal is similar to the conventional three-terminal (3T)-SOT-MRAM. In comparison to the traditional STT-MRAM, the switching times and critical switching voltages are considerably reduced. Furthermore, the full thermal simulations show the significance of the heating process and temperature modeling in MRAM devices as they demonstrate a significantly lower switching time than the one in a constant temperature model.

Impact of Top Electrodes (Cu, Ag, and Al) on Resistive Switching behaviour of Cu-rich Cu2ZnSnS4 (CZTS) Ideal Kesterite.

Cu2ZnSnS4 (CZTS) active material-based resistive random-access memory (RRAM) devices are investigated to understand the impact of three different Cu, Ag, and Al top electrodes. The dual resistance switching (RS) behaviour of spin coated CZTS on ITO /Glass is investigated up to 102 cycles. The stability for all the devices (Cu/CZTS/ITO, Ag/CZTS/ITO, and Al/CZTS/ITO) is investigated up to 103 s in low- (LRS) and high- (HRS) resistance states at 0.2 V read voltage. The endurance up to 102 cycles with 30 ms switching width is showing the stable write and erase current. Weibull cumulative distribution plots suggest that Ag top electrode is relatively more stable for set and reset state with 33.61 and 25.02 shape factors, respectively. The charge carrier transportation is explained by double logarithmic plots, Schottky emission plots, and band diagrams, substantiating that at lower applied electric field intrinsic copper ions dominate in Cu/CZTS/ITO, whereas, at higher electric filed, top electrodes (Cu and Ag) dominate over intrinsic copper ions. Intrinsic Cu+ in CZTS plays a decisive role in resistive switching with Al electrode. Further the impedance spectroscopy measurements suggest that Cu+ and Ag+ diffusion is the main source for the resistive switching with Cu, and Ag electrodes.

Half-metallic ferromagnetism and thermoelectric effect in spinel chalcogenides SrX2S4 (X = Mn, Fe, Co) for spintronics and energy harvesting

Spintronics is an emerging technology in advanced quantum electronics, which has multidirectional applications. In this study, the electronic, magnetic, and thermoelectric characteristics of SrX2S4 (X = Mn, Fe, Co) are computed systematically. The stability in ferromagnetic states is verified by energy released from optimized structures and enthalpy of formation. The Heisenberg model is applied for Curie temperature. The band structures are plotted for both spin ↑ and ↓ configurations, which ensure 100% spin polarization and integer magnetic moments. Furthermore, the metallic behavior in spin ↑ and insulating behavior in spin ↓ confirm half-metallic ferromagnetism. The crystal field energy, direct exchange energy, indirect exchange energy, and exchange constants indicate that ferromagnetism is due to spin of electrons rather than any clusters of transition metals. The effect of thermoelectric parameters on spin functionality of electrons is addressed to enhance the device reliability. The thermoelectric performance is reported by power factor in the temperature span 100–500 K, which is important for energy harvesting.

Spin–orbit coupling of Europa’s ice shell and interior

Europa is an icy ocean world, differentiated into a floating ice shell and solid interior, separated by a global ocean. The classical spin–orbit coupling problem considers a satellite as a single rigid body, but in the case of Europa, the existence of the subsurface ocean enables independent motion of the ice shell and solid interior. This paper explores the spin–orbit coupling problem for Europa from a dynamical perspective, yielding illuminating analytical and numerical results. We determine that the spin behavior of Europa is influenced by processes not captured by the classical single rigid body spin–orbit coupling analysis. The tidal locking process for Europa is governed by the strength of gravity-gradient coupling between the ice shell and solid interior, with qualitatively different behavior depending on the scale of this effect. In this coupled rigid model, the shell can potentially undergo large angular displacements from the solid interior, and the coupling plays an outsize role in the dynamical evolution of the moon, even without incorporating the dissipative effects of shell non-rigidity. We additionally discuss the effects of a realistic viscoelastic shell, and catalogue other torques that we expect to be sub-dominant in Europa’s spin dynamics, or whose importance is unknown. Finally, we explore how the choice of tidal model affects the resulting equilibrium spin state.

Day and night: habitability of tidally locked planets with sporadic rotation

ABSTRACT Tidally locked worlds provide a unique opportunity for constraining the probable climates of certain exoplanets. They are unique in that few exoplanet spin and obliquity states are known or will be determined in the near future: both of which are critical in modelling climate. A recent study shows the dynamical conditions present in the TRAPPIST-1 system make rotation and large librations of the substellar point possible for these planets, which are usually assumed to be tidally locked. We independently confirm the tendency for planets in TRAPPIST-1-like systems to sporadically transition from tidally locked libration to slow rotation using N-body simulations. We examine the nature and frequency of these spin states to best inform energy balance models which predict the temperature profile of the planet’s surface. Our findings show that tidally locked planets with sporadic rotation are able to be in both long-term persistent states and states with prolonged transient behaviour: where frequent transitions between behaviours occur. Quasi-stable spin regimes, where the planet exhibits one spin behaviour for up to hundreds of millennia, are likely able to form stable climate systems while the spin behaviour is constant. 1D energy balance models show that tidally locked planets with sporadic rotation around M-dwarfs will experience a relatively small change in substellar temperature due to the lower albedo of ice in an infrared dominant stellar spectrum. The exact effects of large changes in temperature profiles on these planets as they rotate require more robust climate models, like 3D global circulation models, to better examine.

An Optimization Study for the Electrospun Borate Ester Nanofibers as Light‐Weight, Flexible, and Affordable Neutron Shields for Personal Protection

AbstractIn this manuscript, a borate ester solution, as a precursor, is prepared by combining polyvinyl alcohol (PVA) and boric acid (BA). The precursor is then electrospun to form nanofibers. However, the addition of BA has a negative effect on the spinning behavior by changing the conductivity. The solution's quality is enhanced through use of additives such as glycerol, sodium chloride, and acetic acid. The effect of additives on the viscosity and conductivity of solutions, and their spinning behavior, is investigated. By adjusting electrospinning process variables and solution properties, nanofibers are produced. Fourier transform infrared (FT‐IR) analysis is performed to identify the formation of borate ester as a result of the reaction between PVA and BA. Thermal analysis is used to characterize the thermal stability of the fibers. Scanning electron microscopy (SEM) is used to examine the fiber morphology and diameter distribution. The findings are used to determine the best viscosity–conductivity windows for the production of electrospun borate ester nanofibers. Finally, the ability of optimized nanofibers to capture neutrons is evaluated using an Am‐Be neutron source and a BF3 detector set up. The results of the measurements indicate that the incorporation of BA into PVA nanofibers can enhance their neutron shielding capabilities up to 7.3%.

Spin moment cancelation of high Curie temperature Ir doped ZrO2 gradual atomic change

This paper presents the structural, magnetic properties, and spin moment cancelation phenomenon of the zirconium oxide with a gradual change of zirconium for Iridium. The density functional theory (DFT) is shown to be a key feature of magnetic properties of solid materials treatment. It is shown that a small adjustment of the spin moment (less than 6%) is allowed. The Zr1-xIrxO2 crystal structure deformation leads to a magnetic compensation that occurs at x=0.06. Spin and orbital moments behaviors are discussed. The stability of the alloy compounds is confirmed by energy calculations. The material presents ferromagnetic stability and an indirect exchange coupling with a hybridization effect that permitted the evolution from a non-magnetic to a host material with magnetic properties. The Ir orbitals are set at the Fermi level and are spin polarized which indicates a half metallic behavior then makes the material a good candidate for spintronics’ applications.

Morphology of the abdominal segmental glands and spinning behaviour of Stenus larvae (Coleoptera, Staphylinidae)

We focus on the morphology of the “segmental glands” and their openings in third instar Stenus larvae. The location of the openings was similar in both studied species, with paired rosette-like structures present on the head, all thoracic segments and abdominal segments 1–9. No such openings could be found on the antennae, the maxillary palps, the urogomphi, and the legs as suggested in some older publications. We presume that the glands up to abdominal segment 7 are “adhesive” glands. They are compound glandular units consisting of a secretory syncytium with a common reservoir and a canal cell. The common reservoir is connected through a single efferent duct with the opening of the gland. Glands of abdominal segments 8 and 9 show differences in their length, number of reservoirs, the orientation of the efferent canal, the inner structures of the gland openings towards the exterior and the shape and content of the secretion vesicles indicating that they are silk glands for cocoon building. The spinning behaviour has been observed during the building of the hatching and pupation retreats. The larva first attaches to the substrate with its pygopod, secretes silk droplets from silk gland openings and pulls out a silk filament from the tip of its urogomphi. Whereas L1 and L2 instars produce an open single-layered net, L3 build a closed bi-layered cocoon.

Effects of artificial diet rearing during all instars on silk secretion and gene transcription in Bombyx mori (Lepidoptera: Bombycidae).

Silkworms (Bombyx mori) reared on artificial diets during all instars have the advantages of simplicity and efficiency, year-round production, and reduced risk of poisoning. However, low silk yield remains a challenge, limiting its industrial application. To address this issue, the spinning behavior, nutrient absorption, and transcriptomics of silkworms were investigated. Compared with silkworms reared on mulberry leaves during all instars, those fed with artificial diets showed significantly lower cocoon weight, cocoon shell weight, cocoon shell rate, and silk gland tissue somatic index at the end of the fifth instar (P < 0.01). The spinning duration and crawling distance of silkworms reared on artificial diets were also significantly lower than those reared on mulberry leaves (P < 0.01). Regarding nutrient absorption, the dietary efficiency indexes of silkworms fed with artificial diets were significantly lower than those fed with mulberry leaves, except for the efficiency conversion of digesta to cocoon (P < 0.01). Further RNA-Seq analysis revealed 386 differentially transcribed genes between the 2 groups, with 242 upregulated and 144 downregulated genes. GO enrichment analysis showed that differential transcriptional genes were mainly enriched in organic acid metabolism, oxidation-reduction, and drug catabolism. KEGG enrichment analysis showed that differential transcriptional genes were mainly enriched in genetic information processing and metabolism pathways. Our findings provide new insights into the silk secretion and can serve as a reference for future research and application of silkworms fed with artificial diets.

Synthesis and Characterization of a One-Dimensional Malleable Spin-Crossover Polymer Complex Modified by Methoxy Polyethylene Glycol.

A novel one-dimensional malleable spin-crossover (SCO) complex {[Fe(MPEG-trz)3](BF4)2} has been successfully synthesized by molecular self-assembly between 4-amino-1,2,4-triazoles (MPEG-trz) grafted with a long flexible chain methoxy polyethylene glycol (MPEG) and metallic complex Fe(BF4)2•6H2O. The detailed structure information was illustrated by using FT-IR and 1H NMR measurements, while the physical behaviors of the malleable SCO complexes were systematically investigated by using magnetic susceptibility measurements using superconductivity quantum interference device (SQUID) and differential scanning calorimetry (DSC). This new metallopolymer exhibits a remarkable spin crossover transition behavior, between two spin quantum states (Fe2+ ions): high spin (HS) state (quintet state) and low spin (LS) state (singlet state), at a specific critical temperature with a slender hysteresis loop of 1 K. DFT computations revealed the partial rules of HOMO-LUMO energy levels and spin density distributions of different four-position substituted [Fe(1,2,4-triazole)3]2+ derivatives with different length of repeat units in polymer complexes. This can go a step further to depict the spin and magnetic transition behaviors of SCO polymer complexes. Furthermore, the coordination polymers possess an excellent processability due to an outstanding malleability, which can be easily shaped into a polymer film with spin magnetic switching properties.

On the behaviour of spin–orbit connection of exoplanets

Star–planet interactions play, among other things, a crucial role in planetary orbital configurations by circularizing orbits, aligning the star and planet spin and synchronizing stellar rotation with orbital motions. This is especially true for innermost giant planets, which can be schematized as binary systems with a very large mass ratio. Despite a few examples where spin–orbit synchronization has been obtained, there is no demographic study on synchronous regimes in those systems yet. Here we use a sample of 1,055 stars with innermost planet companions to show the existence of three observational loci of star–planet synchronization regimes. Two of them have dominant fractions of subsynchronous and supersynchronous star–planet systems, and a third less populated regime of potentially synchronized systems. No synchronous star–planet system with a period higher than 40 days has been detected yet. This landscape is different from eclipsing binary systems, most of which are synchronized. We suggest that planets in a stable asynchronous spin state belonging to star–planet systems in a supersynchronized regime offer the most favourable conditions for habitability. An analysis of 1,055 planets around main sequence stars identifies three subsamples of star–planet synchronization: subsynchronized, dominant for periods shorter than 6.2 days; supersynchronized, for periods longer than 13.5 days; and a transitional regime in between. Synchronized systems are a minority, contrary to eclipsing binaries.

Resveratrol loaded native silk fiber-sericin hydrogel double interpenetrating bioactive wound dressing facilitates full-thickness skin wound healing

Wound repair is challenging for traditional wound dressings. New bioactive dressings need to be developed urgently. Herein, we reported a highly bioactive silk protein wound dressing (SPD) with natural silk fiber-sericin hydrogel interpenetrating double network structure, which combines the dual characteristics of natural silk and sericin hydrogel. Silk fiber scaffolds were secreted directly from silkworms bred by regulating their spinning behaviors. Sericin in SPD is obtained by dissolving silkworm cocoons at high temperature and high pressure, while it remains intact activities to self-assemble a hydrogel. To explore the effect of SPD, we first systematically evaluated its physicochemical properties and biological activities in vitro. The SPD exhibits high porosity, prominent mechanical strength, pH-responsive degradability, and excellent anti-oxidation and cell compatibility. Besides, SPD can load and maintain long-term drug release. Based on the satisfactory performance of SPD in vitro, effective in vivo treatment was achieved in a mouse full-thickness wound model, as demonstrated by a significantly accelerated wound healing process, promote the regeneration of hair follicles and sebaceous glands, increased expression of vascular endothelial growth factor, and reduced inflammation. Further, resveratrol was loaded into SPD to enhance the effects of anti-oxidation and anti-inflammation for wound healing. Our investigation shows that SPD with excellent physicochemical and biological properties applied in a murine full-thickness skin wound model resulted in remarkable and efficient acceleration of healing process, which may inspire the design of new, effective, and safer medical materials for tissue regeneration.

Anomalous Spin Textures in a 2D Topological Superconductor Induced by Point Impurities

AbstractTopological superconductors are foreseen as good candidates for the search of Majorana zero modes, where they appear as edge states and can be used for quantum computation. In this context, it becomes necessary to study the robustness and behavior of electron states in topological superconductors when a magnetic or non‐magnetic impurity is present. The focus is on scattering resonances in the bands and on spin texture to know what the spin behavior of the electrons in the system will be. It is found that the scattering resonances appear outside the superconducting gap, thus providing evidence of topological robustness. Non‐trivial and anisotropic spin textures related to the Dzyaloshinskii–Moriya interaction are also found. The spin textures show a Ruderman–Kittel–Kasuya–Yosida interaction governed by Friedel oscillations. It is believed that the results are useful for further studies which consider many‐point‐impurity scattering or a more structured impurity potential with a finite range.

Molecular Photoinduced Charge Separation: Fundamentals and Application

Abstract We have designed and synthesized a number of donor-acceptor linked systems to elucidate the science of photoinduced charge separation. In particular, porphyrin-fullerene and polymer-fullerene linked molecules have been found to be very useful as model systems for addressing issues in excited-state generation, charge separation, and charge dissociation. We have also proposed a new concept, “dynamic exciton” to establish new comprehensive photochemistry dealing with manipulation of locally excited state, charge-transfer state, and charge-separated state involving mutual transformation. Simultaneously, it is pivotal to adopt time-dependent dynamic effects on electron and spin behaviors entangled with movement of atomic nuclei (i.e., vibration, rotation, and fluctuation) and their collective motion into molecular donor-acceptor systems. Versatile dyes for dye-sensitized solar cells as well as donor/acceptor molecules for bulk heterojunction organic solar cells have also been tailored toward better understanding the underlying mechanism as well as improving their photovoltaic performances. Meanwhile, giant dipole moment produced from donor-acceptor linked molecules by light has been successfully utilized to regulate the membrane potential of living biological cells. This is the first example of the use of charge-separated state in optogenetics and is promising as neuronal therapy by light.

Investigations for the use and recyclability of the ionic liquid [MTBDH][AcO] as a solvent in air‐gap‐wet spinning process

AbstractThe direct dissolution of cellulose offers a pathway to production of regenerated textile fibers. However, fiber production in the Lyocell process requires a high recyclability of the solvent. Some compounds from the class of ionic liquids (IL) may have higher dissolving capacities together with a higher thermal stability than the conventional N‐methylmorpholin‐N‐oxide (NMMO), which makes them more valuable in an industrial process. A promising representative of such an advanced solvent for Lyocell process, 7‐Methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene acetate ([MTBDH][AcO]) was investigated in this study. A series of 21 consecutive cellulose dissolving and spinning trials via dry‐jet wet spinning was conducted with the same batch of solvent. In the spinning trials, the cellulose was regenerated into water consisting spinning bath. The solvent was recycled by removing the water from the spin bath via distillation in reduced pressure. Due these drastic changes in the water content of the IL during the whole process, the hydrolytic stability is an important aspect to assess the recyclability of the IL and viability of the whole process. The chemical composition of the IL was monitored by means of NMR spectroscopy. Although there was an increase of hydrolysis level of the solvent, cellulose could be dissolved constantly and spun to obtain staple fibers. The spinning behavior deteriorated slowly along the additional cycles, along with a measured increase in zero‐shear viscosity of the spinning dope. Nevertheless, the physical properties of the obtained fibers were barely influenced by the changes of the ionic liquid.

Disordered topological graphs enhancing nonlinear phenomena.

Complex networks play a fundamental role in understanding phenomena from the collective behavior of spins, neural networks, and power grids to the spread of diseases. Topological phenomena in such networks have recently been exploited to preserve the response of systems in the presence of disorder. We propose and demonstrate topological structurally disordered systems with a modal structure that enhances nonlinear phenomena in the topological channels by inhibiting the ultrafast leakage of energy from edge modes to bulk modes. We present the construction of the graph and show that its dynamics enhances the topologically protected photon pair generation rate by an order of magnitude. Disordered nonlinear topological graphs will enable advanced quantum interconnects, efficient nonlinear sources, and light-based information processing for artificial intelligence.

RF coil efficacy for efficient spin control in low field magnetic resonance experiments

At low magnetic fields (<1 T), the low loss of radio frequency (RF) coils can cause RF pulses, in magnetic resonance (MR) experiments, to suffer from long rise and fall times. When severe, long rise and fall times can result in RF pulses with undesirable and/or unexpected shapes, lengths, and amplitudes leading to inadequate spin control during an MR experiment. Experimentally, the lack of spin control becomes evident in the shape of the nutation curve and the inversion efficiency, the degree to which full inversion is accomplished following a 180° pulse. Lowering the quality factor (Q) of tuned coil is shown to reduce the duration of the rise and fall times. The effects of long rise and fall times on the spin behavior during an MR experiment is explored. It is shown that the inversion efficiency can be used to provide a threshold that ensures high fidelity pulses with adequate spin control.

Study of mesophase pitch based carbon fibers: Structural changes as a function of anisotropic content

This study investigates the synthesis of mesophase pitch (MP) with varying anisotropic (mesophase) content of 19–74% by thermal soaking of isotropic coal tar pitch for different time intervals at 410 °C without using any catalyst/additive and pre-treatment processing. These mesophase pitches were converted into continuous pitch fibers by melt spinning process, then stabilized in air and carbonized at 1000 °C to obtain the carbon fibers. The anisotropic (mesophase) content increases with increasing soaking time period from 11 to 15 h and as a result, alter the various microstructural properties of carbon fibers. Physio-chemical and microstructural properties of prepared MP were systematically studied with TGA, FTIR, Raman spectroscopy, XRD and 1H‐NMR. The overall result suggested enhancement in aromaticity and naphthenic hydrogen with increased anisotropy. Rheological studies were carried out to understand the spinning behavior of MPs. Furthermore, transformation of mesophase pitch into carbon fibers at 1000 °C, showed a decline in the microcrystal properties due to the evolution of gases which create disorderness in the lattice structure. It was observed that the increased anisotropic content improves the microstructure of the mesophase pitch and their resultant carbon fibers as the microstructure attained during mesophase formation is retained during its carbonization.

Quantifying the Variation in the Number of Donors in Quantum Dots Created Using Atomic Precision Advanced Manufacturing

Atomic-precision advanced manufacturing enables unique silicon quantum electronics built on quantum dots fabricated from small numbers of phosphorus dopants. The number of dopant atoms comprising a dot plays a central role in determining the behavior of charge and spin confined to the dots and thus overall device performance. In this work, we use both theoretical and experimental techniques to explore the combined impact of lithographic variation and stochastic kinetics on the number of P incorporations in quantum dots made using these techniques and how this variation changes as a function of the size of the dot. Using a kinetic model of PH3 dissociation augmented with novel reaction barriers, we demonstrate that for a 2 × 3 silicon dimer window the probability that no donor incorporates goes to zero, allowing for certainty in the placement of at least one donor. However, this still comes with some uncertainty in the precise number of incorporated donors (either one or two), and this variability may still impact certain applications. We also examine the impact of the size of the initial lithographic window, finding that the incorporation fraction saturates to δ-layer-like coverage as the circumference-to-area ratio decreases. We predict that this incorporation fraction depends strongly on the dosage of the precursor and that the standard deviation of the number of incorporations scales as ∼√n, as would be expected for a sequence of largely independent incorporation events. Finally, we characterize an array of 36 experimentally prepared multidonor 3 × 3 nm lithographic windows with scanning tunneling microscopy, measuring the fidelity of the lithography to the desired array and the final location of PHx fragments within these lithographic windows. We use our kinetic model to examine the expected variability due to the observed lithographic error, predicting a negligible impact on incorporation statistics. We find good agreement between our model and the inferred incorporation locations in these windows from scanning tunneling microscope measurements.