Spin Concentration Research Articles

Determination of nitrogen spin concentration in diamond using double electron-electron resonance

Diamond has been extensively investigated recently due to a wide range of potential applications of nitrogen-vacancy (NV) defect centers existing in a diamond lattice. The applications include magnetometry and quantum information technologies, and long decoherence time $({T}_{2})$ of NV centers is critical for those applications. Although it has been known that ${T}_{2}$ highly depends on the concentration of paramagnetic impurities in diamond, precise measurement of the impurity concentration remains challenging. In the present work we show a method to determine a wide range of the nitrogen concentration $(n)$ in diamond using a wide-band high-frequency electron spin resonance and double electron-electron resonance spectrometer. Moreover, we investigate ${T}_{2}$ of the nitrogen impurities and show the relationship between ${T}_{2}$ and $n$. The method developed here is applicable for various spin systems in solid and implementable in nanoscale magnetic resonance spectroscopy with NV centers to characterize the concentration of the paramagnetic spins within a microscopic volume.

The influence of oxygen conditioning effect on the permeation properties of polyaniline membranes

ABSTRACTThe effect of oxygen conditioning on the performance of polyaniline (PANI) membranes is presented and discussed. The presence of the conditioning effect in such kind of polymer matrix was confirmed by measuring a variation in spin concentration using electron paramagnetic resonance (EPR) spectroscopy. The observed decrease in spin concentration indicates the presence of the dissolved oxygen incompletely removed from PANI matrix. After the prolonged contact between oxygen and PANI membrane, a pronounced decrease in membrane’s selectivity was observed, which may be explained by the firm and permanent interaction between oxygen molecules and nitrogen paramagnetic centers of PANI and could be considered as a kind of PANI irreversible doping process.

Water accessibility in a membrane-inserting peptide comparing Overhauser DNP and pulse EPR methods.

Water accessibility is a key parameter for the understanding of the structure of biomolecules, especially membrane proteins. Several experimental techniques based on the combination of electron paramagnetic resonance (EPR) spectroscopy with site-directed spin labeling are currently available. Among those, we compare relaxation time measurements and electron spin echo envelope modulation (ESEEM) experiments using pulse EPR with Overhauser dynamic nuclear polarization (DNP) at X-band frequency and a magnetic field of 0.33 T. Overhauser DNP transfers the electron spin polarization to nuclear spins via cross-relaxation. The change in the intensity of the (1)H NMR spectrum of H2O at a Larmor frequency of 14 MHz under a continuous-wave microwave irradiation of the nitroxide spin label contains information on the water accessibility of the labeled site. As a model system for a membrane protein, we use the hydrophobic α-helical peptide WALP23 in unilamellar liposomes of DOPC. Water accessibility measurements with all techniques are conducted for eight peptides with different spin label positions and low radical concentrations (10-20 μM). Consistently in all experiments, the water accessibility appears to be very low, even for labels positioned near the end of the helix. The best profile is obtained by Overhauser DNP, which is the only technique that succeeds in discriminating neighboring positions in WALP23. Since the concentration of the spin-labeled peptides varied, we normalized the DNP parameter ϵ, being the relative change of the NMR intensity, by the electron spin concentration, which was determined from a continuous-wave EPR spectrum.

Low energy properties of the Kondo chain in the RKKY regime

We study the Kondo chain in the regime of high spin concentration where the low energy physics is dominated by the Ruderman–Kittel–Kasuya–Yosida interaction. As has been recently shown (Tsvelik and Yevtushenko 2015 Phys. Rev. Lett. 115 216402), this model has two phases with drastically different transport properties depending on the anisotropy of the exchange interaction. In particular, the helical symmetry of the fermions is spontaneously broken when the anisotropy is of the easy plane type. This leads to a parametrical suppression of the localization effects. In the present paper we substantially extend the previous theory, in particular, by analyzing a competition of forward- and backward- scattering, including into the theory short range electron interactions and calculating spin correlation functions. We discuss applicability of our theory and possible experiments which could support the theoretical findings.

Coherence Times of Large-Spin Ensemble in Transient Regime

Rabi oscillations in the ensemble of weakly interacting electron or nuclear spins in solids are theoretically studied. A statistical theory which allows for calculation of the coherence times in the transient regime is presented in the general case of arbitrary spin value \(\ge \)1/2. Analytical expressions of the coherence times depending on the spin, temperature, spin concentration, and the Rabi frequency are obtained.

The effect of solvent on the synthesis and physicochemical properties of poly(3,4-ethylenedioxypyrrole)

Poly(3,4-ethylenedioxypyrrole), PEDOP, is a versatile compound, which has attracted significant scientific interest in the recent years. The wide range of its actual and prospective applications underlines the need for a comprehensive study of this material and identification of factors, allowing the physicochemical properties of PEDOP and its derivatives to be tailored for specific purposes. In this paper, we present the results of our investigation of the physicochemical properties of PEDOP, involving electrochemical, spectroelectrochemical and microscopic analysis. The electrochemical synthesis of PEDOP was performed in solvents of varying polarity and protic/aprotic nature, i.e. H2O, CH3CN and CH2Cl2, by means of cyclic voltammetry. Raman spectroscopy was applied in order to investigate the chemical structure of PEDOP synthesised under varying conditions. ESR measurements allowed the observation of changes in spin concentration as a function of applied potential and analysis of the stability of formed radical anions. UV–vis spectroelectrochemistry was applied to determine the value of optical band gap of PEDOP. The surface morphology of fabricated PEDOP layers was investigated via scanning electron microscopy.

Influence of disorder on ageing and memory effects in non-equilibrium critical dynamics of 3D Ising model relaxing from an ordered state

We have performed a numerical investigation of the influence of disorder on the dynamical non-equilibrium evolution of a 3D site-diluted Ising model from a low-temperature initial state with magnetization m0 = 1. It is shown that two-time dependences of the autocorrelation and integrated response functions for systems with spin concentrations p = 1.0, 0.95, 0.8, 0.6 and 0.5 demonstrate ageing properties with anomalous slowing-down relaxation and violation of the fluctuation-dissipation ratio. It was revealed that during non-equilibrium critical dynamics in the long-time regime the autocorrelation functions for diluted systems are extremely slow due to the pinning of domain walls on impurity sites. We have found that the fluctuation-dissipation ratio for diluted systems with spin concentration p < 1 while the pure system is characterized by . The autocorrelation function power-law delay becomes the same as for the time dependence of the magnetization in the critical point and is characterized by exponent . Also, for diluted systems we reveal memory effects for critical evolution in the ageing regime with realization of cyclic temperature change and quenching at .

Physics of coal methane: decisive role of iron compounds

The role of iron in formation of the coal methane is clarified based on the studies performed on the coal samples taken from different mines in Donetsk coal basin. Using Mossbauer spectroscopy, a correlation is found between the iron content and methane capacity of coal seams. By means of electron paramagnetic resonance, it is found that iron increases the concentration of non-compensated electron spins, i.e. dangled bonds at the carbon atoms. These bonds can be occupied by hydrogen atoms as a prerequisite of methane formation. The two-valence iron is shown to be the most effective in the increase of spin concentration. By using the ion mass spectrometry, the modelling of methane formation is carried out on the mechanical mixture of the iron-free reactor graphite, iron compounds and diluted sulphuric acid as a source of hydrogen atoms. The proposed mechanism is also confirmed by methane formation in the mixture of iron compounds and the coal from the mine where the iron and methane are practically absent.

Zeros of Partition Function and Critical Exponents of the 3D Diluted Ising Model

We used a Monte Carlo simulation of the structurally disordered three dimensional Ising model. For the systems with spin concentrations p = 0.95 ,0.8, 0.6 and 0.5 we calculated the correlation-length critical exponent ν by finite-size scaling. Extrapolations to the thermodynamic limit yield ν(0.95) = 0.705(5) ,ν(0.8) = 0.711(6),ν(0.6) = 0.736(6) and ν(0.5) = 0.744(6). These results are compatible with some previous estimates from a variety of sources. The analysis of the results demonstrates the nonuniversality of the critical behavior in the disordered Ising model.

The Effect of Adsorbed Molecules on Electronic Structure and Magnetic Properties of Nanographites

The results of investigation of changes in electronic structure and magnetic properties of multilayer graphene nanoclusters (nanographites) occurring during their interaction with adsorbed chlorine molecules are presented. The found reversible decrease in the density of states of current carriers D(EF) at the Fermi energy EF can be explained by the spin-splitting of edge π-electron states in nanographites induced by the enhancement of electron-electron interactions due to increase of the D(EF) at partial transfer of the electron density from nanographites to chlorine adatoms. The revealed irreversible decrease in the concentration of localized spins indicates that the electron spins of 3p-orbitals of chlorine and unpaired (dundling) σ-orbitals of edge carbon atoms are coupled also at this interaction, i.e. the edge covalent compound of nanographite with chlorine forms. Character of changes in the spin-relaxation rate of π-electrons depending on the amount of adsorbed chlorine molecules and on temperature in chlorinated samples are also consistent with the above model of nanographite-chlorine interaction.

Peculiarities of Non-Equilibrium Critical Behavior for 3D Diluted Ising Model with Evolution from Low-Temperature Initial State

The Monte Carlo description of aging properties in nonequilibrium critical behaviour of 3D site-diluted Ising model is considered with evolution from ordered initial state with wide range of spin concentrations. At first, it was shown, that pinning of domain walls on defects leeds to a sharp change of aging properties in diluted systems in comparison with pure system. Therefore, the asymptotic value of the fluctuation-dissipative relation becomes equal to null for diluted systems, while for pure system = 0.784(5).

Phosphazene-cored star polymer bearing redox-active side groups as a cathode-active material in Li-ion batteries

A new hexa-armed star polymer bearing 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-pending polymer chains emanating from a phosphazene core (P2) was prepared and used as the cathode material in Li-ion battery assembly. The properties of the assembled battery (BP2) were compared with those of BL2 assembled using its linear counterpart (L2). Their spin concentrations investigated via solution electron spin resonance (ESR) measurements were found to be almost the same. The charge/discharge capacities and energy densities of BP2 were considerably higher than those of BL2. However, they exhibited comparable charge/discharge efficiencies and their discharge capacities dropped to similar percentages of their initial values.

Effect of Localized Spin Concentration on Giant Magnetoresistance in Molecular Conductor TPP[FexCo1−x(Pc)(CN)2]2

We studied the effect of the localized spin concentration on the giant magnetoresistance (GMR) and the charge order (CO) in the phthalocyanine (Pc) molecular conductors TPP[FexCo1−x(Pc)(CN)2]2 (TPP = tetraphenylphosphonium), in which the localized spin concentration can be controlled by adjusting the Fe concentration x. Resistivity studies indicated that the CO state was stabilized by localized spins. The negative magnetoresistance was observed even in the region of a localized spin concentration of as low as about 5%. In the high-concentration region, the negative magnetoresistance changed into a positive one at low temperatures. This result shows that a magnetic field stabilizes the CO state, unless the magnetic field is sufficiently strong to break the antiferromagnetic order of the localized spins.

High yield and facile microwave-assisted synthesis of conductive H2SO4 doped polyanilines

The microwave-assisted synthesis of polyaniline (PANI) was performed using ammonium persulphate (APS) as oxidizing agent in 0.5 M–2.5 M concentration range of aqueous sulphuric acid (H2SO4) at 93 W applied microwave power of 10 min duration. The microwave (MW) synthesized PANIs had 3 times higher yield in comparison to PANI samples prepared using a classical method, CS (0 W MW power) at the same temperature for 10 min synthesis duration period. Fourier Transform Infrared (FTIR) and UV–Vis spectroscopies confirmed the formation of PANI structure in all products. The influence of H2SO4 acid dopant on the spin concentration of MW and CS H2SO4 doped PANI samples were examined by EPR spectroscopy, while the morphological characteristics were investigated by using scanning electron microscopy (SEM). XRD results showed amorphous phases in both MW and CS H2SO4 doped PANI samples. Conductivity measurements revealed ∼1.5 times higher conductivity values for MW H2SO4 doped PANI samples in comparison with PANI samples prepared by the CS method under same condition. The influence of sulfate anion in comparison to chloride anion as a dopant on morphological, dopant levels and conductivity properties of MW PANI samples were also investigated.

Non-equilibrium critical vortex dynamics of disordered 2D XY-model

Vortex dynamics and clustering in non-equilibrium critical relaxation of disordered 2D XY-model are investigated for different initial states. Time dependencies of vortex concentration and clusters sizes are studied for different spin concentrations. The anomalous slow down of clustering in disordered system are explained by pinning of vortices on defects. The calculated temperature dependence of transverse stiffness allows to estimate critical temperature Tbkt and applicability of spin-wave approximation for disordered system.

DNP with Trityl Radicals in Deuterated Polyethylene

Chemically doping with trityl radicals was performed in fully deuterated polyethylene. The behavior of paramagnetic centers has been investigated by ESR X-band spectrometer. The highest deuteron polarization was 8% at 2.5 T and 1 K with a spin concentration of [Formula: see text] spins/g.

Effect of Sm3+-Gd3+ co-doping on dielectric properties of Mn-Zn ferrites synthesized via combustion route

Nanocrystalline Mn0.4 Zn0.6SmxGdyFe2-(x+y)O4where x and y = 0.01,0.02,0.03,0.04 and 0.05 were synthesized by Solution combustion method. The as prepared samples were characterized by X-ray diffractometer (XRD), Transmission electron microscopy (TEM) and Vibrating sample Magnetometer (VSM) at room temperature. From the XRD the crystallite size were found increases with the increase of Sm3+-Gd3+ ions concentration while lattice parameter found to decreases. The real and imaginary part of permittivity (ε′ and ε′′) were undertaken in the wide frequency range 1GHz to 5GHz at room temperature. It is found that the real and imaginary part of permittivity’s are increasing with increasing Sm3+ and Gd3+ concentration. The magnetic behaviour of as synthesized nano ferrites reveals that, the saturation magnetization (MS), remanence magnetization (MR) is increasing with increasing Sm and Gd concentration. The g-value, peak-to-peak linewidth and spin concentration evaluated from EPR spectra correlated with cations occupancy. These electromagnetic properties clearly indicates that the synthesized materials are the good candidates for L and C band frequency.

Microscopic signature of insulator-to-metal transition in highly doped semicrystalline conducting polymers in ionic-liquid-gated transistors

Electronic state of charge carriers, in particular, in highly doped regions, in thin-film transistors of a semicrystalline conducting polymer poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene), has been studied by using field-induced electron spin resonance (ESR) spectroscopy. By adopting an ionic-liquid gate insulator, a gate-controlled reversible electrochemical hole-doping of the polymer backbone is achieved, as confirmed from the change of the optical absorption spectra. The edge-on molecular orientation in the pristine film is maintained even after the electrochemical doping, which is clarified from the angular dependence of the g value. As the doping level increases, spin 1/2 polarons transform into spinless bipolarons, which is demonstrated from the spin-charge relation showing a spin concentration peak around 1%, contrasting to the monotonic increase in the charge concentration. At high doping levels, a drastic change in the linewidth anisotropy due to the generation of conduction electrons is observed, indicating the onset of metallic state, which is also supported by the temperature dependence of the spin susceptibility and the ESR linewidth. Our results suggest that semicrystalline conducting polymers become metallic with retaining their molecular orientational order, when appropriate doping methods are chosen.

Effect of ultrasonic vibration on the morphology of bubble-electrospun nanofibers

In this study, biodegradable poly (vinyl alcohol) (PVA) polymer solutions with various concentrations are treated by ultrasonic vibration and successfully bubble-electrospun to fabricate nanofibers. It shows that the ultrasonic vibration time significantly affects the viscosity and electrical conductivity of PVA solution, especially the morphology of the obtained nanofibers which can be characterized by the scanning electron microscopy (SEM). The diameters of the nanofibers are measured at the spinning concentration of 11 % of PVA solution. The novel strategy can be applied to improve solution spinnability and produce much finer nanofibers than without application of vibration technology.

Phase transition and surface sublimation of a mobile Potts model.

We study in this paper the phase transition in a mobile Potts model by the use of Monte Carlo simulation. The mobile Potts model is related to a diluted Potts model, which is also studied here by a mean-field approximation. We consider a lattice where each site is either vacant or occupied by a q-state Potts spin. The Potts spin can move from one site to a nearby vacant site. In order to study the surface sublimation, we consider a system of Potts spins contained in a recipient with a concentration c defined as the ratio of the number of Potts spins N(s) to the total number of lattice sites N(L)=N(x)×N(y)×N(z). Taking into account the attractive interaction between the nearest-neighboring Potts spins, we study the phase transitions as functions of various physical parameters such as the temperature, the shape of the recipient, and the spin concentration. We show that as the temperature increases, surface spins are detached from the solid phase to form a gas in the empty space. Surface order parameters indicate different behaviors depending on the distance to the surface. At high temperatures, if the concentration is high enough, the interior spins undergo a first-order phase transition to an orientationally disordered phase. The mean-field results are shown as functions of temperature, pressure, and chemical potential, which confirm in particular the first-order character of the transition.