Spin Concentration Research Articles

Decoherence from dipolar interspin interactions in molecular spin qubits

The realization of spin-based logical gates crucially depends on magnetically coupled spin qubits. Thus, understanding decoherence when spin qubits are in close proximity will become a roadblock to overcome. Herein, we propose a method free of fitting parameters to evaluate the qubit phase memory time ${T}_{m}$ in samples with high electron spin concentrations. The method is based on a model aimed to estimate magnetic nuclear decoherence [P. C. E. Stamp and I. S. Tupitsyn, Phys. Rev. B 69, 014401 (2004)]. It is applied to a ground-spin $J=8$ magnetic molecule 1 displaying atomic clock transitions, namely ${{[\mathrm{H}{\mathrm{o}}^{\mathrm{III}}{({\mathrm{W}}_{5}{\mathrm{O}}_{18})}_{2}]}^{9}}^{\ensuremath{-}}$, which remarkably increase ${T}_{m}$ at unusually high electron-spin concentrations. Our approach unveils the causes that limit the coherence reached at the clock transitions in challenging systems such as 1, where recent models fail.

Aluminothermic synthesis of [Ca24Al28O64]4+(4e−) electride ceramic directly from Ca3Al2O6 precursor

Mayenite-derived electride [Ca24Al28O64]4+(4e−) has been successfully synthesized via an aluminothermic reaction of Ca3Al2O6 (C3A), Al2O3, and Al powders at 1070 °C for 10 min using spark plasma sintering (SPS) process in a vacuum. The C3A precursors were directly derived from high temperature calcinating in an ambient atmosphere. The as-synthesized C12A7:e− exhibits an electron density of ∼2.3 × 1021cm−3, a spin concentrations of ∼6.7 × 1019cm−3 and optical absorption bands of 0.5eV and 2.48ev at room temperature. Electronic structure was also evaluated by electron paramagnetic resonance (EPR). The appearance of Dysonian characteristic, a typical feature of good electronic conductors, strongly suggested the formation of conductive mayenite structure. This developed and efficient route not only proposes an modified precursor for the synthesis of high-quality C12A7:e− but also provide more comprehensive insights into mayenite research.

Understanding the Linewidth of the ESR Spectrum Detected by a Single NV Center in Diamond

Spectral analysis of electron spin resonance (ESR) is a powerful technique for various investigations including characterization of spin systems, measurements of spin concentration, and probing spin dynamics. The nitrogen-vacancy (NV) center in diamond is a promising magnetic sensor enabling improvement of ESR sensitivity to the level of a single spin. Therefore, understanding the nature of the NV-detected ESR (NV-ESR) spectrum is critical for applications to nanoscale ESR. Within this work, we investigate the linewidth of NV-ESR from single substitutional nitrogen centers (called P1 centers). NV-ESR is detected by a double electron-electron resonance (DEER) technique. By studying the dependence of the DEER excitation bandwidth on the NV-ESR linewidth, we find that the spectral resolution is improved significantly and eventually limited by inhomogeneous broadening of the detected P1 ESR. Moreover, we show that the NV-ESR linewidth can be as narrow as 0.3 MHz.

Operando Electron Paramagnetic Resonance for Elucidating the Electron Transfer Mechanism of Coenzymes

One of the most important challenges in chemistry with direct implication in biochemistry is probing the mechanism of electron transfer originating from biological molecules. On the basis of protein film voltammetry, mediated electron transfer and molecular adsorption followed by heterogeneous catalysis result in similar responses for steady-state currents; both processes increase the Faradaic current at a low overpotential. This is typical of NAD-dependent alcohol dehydrogenase (ADH), an oxidoreductase enzyme that uses the interconversion of NAD+/NADH coenzyme to catalyze the oxidation of alcohol to aldehyde. We propose a setup based on operando electron paramagnetic resonance (EPR) spectroscopy to investigate the NADH/NAD+ redox reaction and introduce how to probe free electrons on a carbon electrode surface and correlate them with the electrocatalytic mechanism. Since knowledge of the g-factor may provide information about the electronic structure of the paramagnetic center at the carbon surface, it was found that the concentration of unpaired free electrons responds to both applied overpotential and NADH oxidation, enabling measurement of the in situ dynamics of the electron transfer reaction. A new correlation for the spin concentration reveals an increasing number of free unpaired electrons with increasing applied overpotential and NADH oxidation, which corroborates the controversial hypothesis that quinone groups act as electrocatalysts and not as redox mediators toward the oxidation of NADH to NAD+. Furthermore, operando EPR provides useful information in probing the electron transfer dynamics on a carbon surface and may be extended to other chemical systems involving electron transfer reactions.

Gem-Diethyl Pyrroline Nitroxide Spin Labels: Synthesis, EPR Characterization, Rotamer Libraries and Biocompatibility.

The availability of bioresistant spin labels is crucial for the optimization of site‐directed spin labeling protocols for EPR structural studies of biomolecules in a cellular context. As labeling can affect proteins’ fold and/or function, having the possibility to choose between different spin labels will increase the probability to produce spin‐labeled functional proteins. Here, we report the synthesis and characterization of iodoacetamide‐ and maleimide‐functionalized spin labels based on the gem‐diethyl pyrroline structure. The two nitroxide labels are compared to conventional gem‐dimethyl analogs by site‐directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy, using two water soluble proteins: T4 lysozyme and Bid. To foster their use for structural studies, we also present rotamer libraries for these labels, compatible with the MMM software. Finally, we investigate the “true” biocompatibility of the gem‐diethyl probes comparing the resistance towards chemical reduction of the NO group in ascorbate solutions and E. coli cytosol at different spin concentrations.

Facile fabrication and characterization on alginate microfibres with grooved structure via microfluidic spinning.

Alginate microfibres were fabricated by a simple microfluidic spinning device consisting of a coaxial flow. The inner profile and spinnability of polymer were analysed by rheology study, including the analysis of viscosity, storage modulus and loss modulus. The effect of spinning parameters on the morphological structure of fibres was studied by SEM, while the crystal structure and chemical group were characterized by FTIR and XRD, respectively. Furthermore, the width and depth of grooves on the fibres was investigated by AFM image analysis and the formation mechanism of grooves was finally analysed. It was illustrated that the fibre diameter increased with an increase in the core flow rate, whereas on the contrary of sheath flow rate. Fibre diameter exhibited an increasing tendency as the concentration of alginate solution increased, and the minimum spinning concentration of alginate solution was 1% with the finest diameter being around 25 µm. Importantly, the grooved structure was obtained by adjusting the concentration of solutions and flow rates, the depth of groove increased from 278.37 ± 2.23 µm to 727.52 ± 3.52 µm as the concentration varied from 1 to 2%. Alginate fibres, with topological structure, are candidates for wound dressing or the engineering tissue scaffolds.

Organic Radical-Linked Covalent Triazine Framework with Paramagnetic Behavior.

The production of multifunctional pure organic materials that combine different sizes of pores and a large number of electron spins is highly desirable due to their potential applications as polarizers for dynamic nuclear polarization-nuclear magnetic resonance and as catalysts and magnetic separation media. Here, we report a polychlorotriphenylmethyl radical-linked covalent triazine framework (PTMR-CTF). Two different sizes of micropores were established by N2 sorption and the presence of unpaired electrons (carbon radicals) by electron spin resonance and superconducting quantum interference device-vibrating sample magnetometer analyses. Magnetization measurements demonstrate that this material exhibits spin-half paramagnetism with a spin concentration of ∼2.63 × 1023 spins/mol. We also determined the microscopic origin of the magnetic moments in PTMR-CTF by investigating its spin density and electronic structure using density functional theory calculations.

Tailoring of carbonized polypyrrole nanotubes core by different polypyrrole shells for oxygen reduction reaction selectivity modification

By using methyl orange template, polypyrrole nanotubes were obtained by the oxidative polymerization of pyrrole. The nanotubes were carbonized in inert atmosphere to nitrogen-enriched carbon nanotubes. These were subsequently coated with 20 wt% of polypyrrole prepared in the absence or the presence of anionic dyes (methyl orange or Acid Blue 25). The morphology of all the samples was examined by the electron microscopies, FTIR and Raman spectroscopies. Moreover, X-ray photoelectron spectroscopy and elemental analysis were used to prove the chemical structure and the successful coating process. Electron paramagnetic resonance analysis was used to calculate the spin concentrations. Significant impact of coating method is evidenced with neat polypyrrole coating providing a two-fold capacitance increase compared to uncoated nanotubes, while coating in the presence of Acid Blue 25 decreasing it slightly. With respect to oxygen reduction reaction, coatings irreversibly transformed in the first few cycles in the presence of the products of O2 reduction, presumably hydrogen peroxide, altering the oxygen reduction mechanism. This transformation allows the tailoring of the polymeric shell, over ORR active carbonaceous core, and tuning of the catalyst selectivity and optimization of materials performance for a given application – from alkaline fuel cells to hydrogen peroxide generation.

Peculiarities of non-equilibrium critical behavior of site-diluted 2D Ising model

The results of a numerical Monte Carlo study of features of nonequilibrium critical behavior in a two-dimensional pure and structurally disordered Ising models are presented with realization of evolution from different initial states within the wide range of spin concentrations p = 1.0, 0.95, 0.9, 0.85, 0.8, 0.75, and 0.7. Analysis of the two-time dependences of the autocorrelation function and dynamic susceptibility revealed a substantial influence of the initial states on the aging effects. The violation of the fluctuation-dissipation theorem is studied, and the asymptotic values of the fluctuation-dissipation ratio are calculated.

The critical behavior of the two-dimensional three-state Potts model on a triangular lattice with quenched disorder

The critical behavior of the two-dimensional three-state antiferromagnetic Potts model with quenched disorder on a triangular lattice is investigated by the Monte Carlo method. Static critical exponents for the susceptibility γ, the magnetization β, the specific heat α, and the exponent of the correlation radius ν at spin concentrations p = 0.90; 0.80; 0.70; 0.65 are calculated on the basis of the finite-size scaling theory. The critical exponents are found to be increasing with a rise in disorder without violating the feasibility of scaling equation 2βν+γν=d, while relations γ/ν and β/ν remain unchanged. This behavior of the critical exponents we have come to associate with the weak universality of a critical behavior typical for disordered systems.

Computer simulation of the critical behavior of highly diluted low-dimensional antiferromagnetic systems on a triangular lattice

A computer simulation of the critical behavior of a two-dimensional highly diluted 3-state antiferromagnetic Potts model on a triangular lattice is performed. The calculations are done for systems with periodic boundary conditions at spin concentrations p equal to 0.70 and 0.65. Systems with linear dimensions L×L = N, L = 20–144 are considered. Based on the theory of finite-dimensional scaling, the static critical exponents of heat capacity α, susceptibility γ, order parameter β, and critical index ν for the correlation radius are calculated. It is numerically shown that the calculated critical exponents vary with changes in the spin concentration p, while the ratios β/ν and γ/ν remain unchanged within error, showing a weak universality of the critical behavior of disordered systems.

Non‐affine fiber kinematics in arterial mechanics: a continuum micromechanical investigation

AbstractThere is growing experimental evidence for non‐affine deformations occurring in different types of fibrous soft tissues; meaning that the fiber orientations do not follow the macroscopic deformation gradient. Suitable mathematical modeling of this phenomenon is an open challenge, which we here tackle in the framework of continuum micromechanics. From a rate‐based analogon of Eshelby's inhomogeneity problem, we derive strain and spin concentration tensors relating macroscopic strain rate tensors applied to the boundaries of a Representative Volume Element (RVE), to strain rates and spins within the tissue microstructure, in particular those associated with fiber rotations due to external mechanical loading. After presenting suitable algorithms for integrating the resulting rate‐type governing equations, a first relevance check of the novel modeling approach is undertaken, by comparison of model results to recent experiments performed on the adventitia layer of rabbit carotid tissue.

Tidal stripping and post-merger relaxation of dark matter haloes: causes and consequences of mass-loss

We study the properties of distinct dark matter halos (i.e., those that are not subhalos) that have a final virial mass $M_{\mathrm{vir}}$ at $z = 0$ less than their peak mass ($M_{\mathrm{peak}}$) in the Bolshoi-Planck cosmological simulation. We identify two primary causes of halo mass loss: relaxation after a major merger and tidal stripping by a massive neighbouring halo. Major mergers initially boost $M_{\mathrm{vir}}$ and typically cause the final halo to become more prolate and less relaxed and to have higher spin and lower NFW concentration. As the halo relaxes, high energy material from the recent merger gradually escapes beyond the virial radius, temporarily resulting in a net negative accretion rate that reduces the halo mass by $5-15\%$ on average. Halos that experience a major merger around $z = 0.4$ typically reach a minimum mass near $z = 0$. Tidal stripping mainly occurs in dense regions, and it causes halos to become less prolate and have lower spins and higher NFW concentrations. Tidally stripped halos often lose a large fraction of their peak mass ($> 20\%$) and most never recover (or even reattain a positive accretion rate). Low mass halos can be strongly affected by both post-merger mass loss and tidal stripping, while high mass halos are predominantly influenced by post-merger mass loss and show few signs of significant tidal stripping.

Optimization of Temperature Sensitivity Using the Optically Detected Magnetic-Resonance Spectrum of a Nitrogen-Vacancy Center Ensemble

Temperature sensing with nitrogen vacancy (NV) centers using quantum techniques is very promising and further development is expected. Recently, the optically detected magnetic resonance (ODMR) spectrum of a high-density ensemble of the NV centers was reproduced with noise parameters [inhomogeneous magnetic field, inhomogeneous strain (electric field) distribution, and homogeneous broadening] of the NV center ensemble. In this study, we use ODMR to estimate the noise parameters of the NV centers in several diamonds. These parameters strongly depend on the spin concentration. This knowledge is then applied to theoretically predict the temperature sensitivity. Using the diffraction-limited volume of 0.1 micron^3, which is the typical limit in confocal microscopy, the optimal sensitivity is estimated to be around 0.76 mK/Hz^(1/2) with an NV center concentration of 5.0e10^17/cm^3. This sensitivity is much higher than previously reported sensitivities, demonstrating the excellent potential of temperature sensing with NV centers.

REVERSIBLE CHANGES OF EDGE Π-ELECTRONIC STATES OF MULTILAYER GRAPHENE NANOCLUSTERS UNDER INFLUENCE OF ADSORBED CHLORINE MOLECULES

The reversible decrease in the density of states of current carriers D(EF) at the Fermi level EF for nanographites - structural blocks of activated carbon fibers, at their interaction with adsorbed chlorine molecules, has been found. It has been shown that this effect can be explained by the spin-splitting of edge π-electronic states in nanographites induced by the enhancement of electron-electron interactions due to increase in the D(EF) at partial transfer of the electron density from adsorbent to adsorbate. The revealed irreversible decrease in the concentration of localized spins at nanographite chlorination indicates that the spins of electrons of unsaturated (dangling) σ-orbitals of edge carbon atoms and those of chlorine 3p-orbitals are coupled at this interaction, i.e. the edge covalent compound of nanographite with chlorine forms.

Preparation and Characterization of Alphitobius diaperinus Melanin

Melanin with a high antioxidant and sorption activity comparable to that of synthetic dioxyphenylalanine (DOPA)-melanin was isolated from the biomass of the darkling beetle Alphitobius diaperinus. The pigment was extracted with a solution of potassium hydroxide, followed by precipitation with concentrated hydrochloric acid and hydrolysis of the resulting precipitate with the same acid. The electron paramagnetic resonance (EPR) signal of melanin was characteristic of eumelanins with a spin concentration of 4.9 × 1017 spin per 1 g of dry weight. The melanin concentration that induced 50% inhibition of peroxidation was 9.2 μg/mL (the analogous concentration of DOPA-melanin was 8.0 μg/mL). The maximum of methylene-blue binding to the beetle melanin was 700 mg of dye per 1 g of dry weight of the preparation. The lipid-free melanin preparation exhibited antiradical activity.

Spin dynamics in graphene-like nanocarbon, graphene and their nitrogen adatom derivatives

Ulterior computational device is atomic electron in which information route would be precision spin gyration. This demands to investigate spin dynamics in realistic graphene. Our scenario presents spin transport data obtained using electron spin resonance spectroscopy, over 123–473 K for graphene, graphene-like nanocarbon (GNCs) and their nitrogen (N)-doped derivatives. Variations in dispersion widths and anisotropy in effective g-factor indicated modifications in spin–lattice, and spin–spin relaxation time, for both systems after N loading. Particularly, for GNCs contributions of orbital moments to spin inhomoginities are reduced. It resembles with variations observed for spin–orbit coupling constant and spin-flip factor. Flip of spin is more favorable, for N-GNCs, due to retardation in momentum- and spin relaxation rate. Nitrogen narrowed down mid gap states in GNCs and has profound impact on modifications in pseudo chemical potential with reduced density of states, effective magnetic moment, and spin and defect concentration. The variations in spin parameters are opposite, especially, for N-graphene. The spin susceptibility indicated that, there are ~ 10 non-interacting spins per 100 carbon atoms in graphene, and GNCs which is reduced by 50%, especially, for spin correlated, N-GNCs. Atomically engineered spin degrees of constraints are useful for spintronic applications.

Computer Simulation of Critical Behavior of Two-Dimensional Weakly Diluted Antiferromagnetic Potts Model on a Triangular Lattice

The critical behavior of a two-dimensional weakly diluted antiferromagnetic Potts model with spin states q = 3 on a triangular lattice is computationally simulated. The systems with periodic boundary conditions were calculated, when spin concentrations p were 1.0 and 0.9. Systems with linear dimensions L × L = N and L = 9–144 were considered. Static critical exponents of heat capacity α, the susceptibility γ, the order parameter β, and critical exponent ν for a correlation radius are calculated based on a theory of finite-dimensional scaling.

Multinuclear Detection of Nuclear Spin Optical Rotation at Low Field.

We describe the multinuclear detection of nuclear spin optical rotation (NSOR), an effect dependent on the hyperfine interaction between nuclear spins and electrons. Signals of 1H and 19F are discriminated by frequency in a single spectrum acquired at sub-millitesla field. The simultaneously acquired optical signal along with the nuclear magnetic resonance signal allows the calculation of the relative magnitude of the NSOR constants corresponding to different nuclei within the sample molecules. This is illustrated by a larger NSOR signal measured at the 19F frequency despite a smaller corresponding spin concentration. Second, it is shown that heteronuclear J-coupling is observable in the NSOR signal, which can be used to retrieve chemical information. Multinuclear frequency and J resolution can localize optical signals in the molecule. Properties of electronic states at multiple sites in a molecule may therefore ultimately be determined by frequency-resolved NSOR spectroscopy at low field.

Effects of Superaging and Percolation Crossover on the Nonequilibrium Critical Behavior of the Two-Dimensional Disordered Ising Model

A Monte Carlo study of the specific features of the nonequilibrium critical behavior has been performed for the two-dimensional “pure” and structurally disordered Ising models in the course of their evolution from the low-temperature initial state at spin concentrations p = 1.0, 0.9, and 0.8. It is shown for the first time that the pinning of domain walls by structural defects leads to the anomalously strong slowing down in the evolution of the autocorrelation function characterized by the superaging effect with exponents μ = 6.25(5) and μ = 6.75(5) for the model with the spin concentrations p = 0.9 and 0.8, respectively. The pure model exhibits the conventional aging with the exponent μ = 1. It is found that the superaging effects in structurally disordered systems lead to vanishing of the limiting fluctuation−dissipation ratio X∞, whereas X∞ = 0.751(24) for the pure model.