Conduction Electron Spin Resonance Signal Research Articles

Paramagnetic defects in hydrothermally grown few-layered MoS2 nanocrystals

Abstract

Local structure and paramagnetic properties of the nanostructured carbonaceous material shungite.

Using a scanning electron microscopy, elemental analysis, electron paramagnetic resonance, and Raman scattering methods, two types of the shungite materials (Sh-II from Zazhogino deposit and shungite from a commercial filter (ShF)), with different carbon content and porosity, are studied in this work. It was established by scanning electron microscopy data that the structure of the shungite samples is formed by a micron-size agglomeration of carbon and silicon dioxide clusters. It is found from the Raman data that carbon fraction is formed from sp2-hybridized clusters, size of which increases from 9 up to 12 nm after annealing of the samples. High conductivity of shungite is found to belong to the carbon nanoclusters of different sizes. Big clusters give the conduction electron spin resonance signal with a Dysonian line shape with variable g-factor and line width.The careful search of the nature of two other narrow electron paramagnetic resonance signals in shungite, which used to be prescribed to fullerene-like molecules, is fulfilled. Here, it is shown that the oxygen-deficient E'γ centers are responsible for these signals. A strong correlation is revealed between the concentration of Е'γ centers and the line width of conduction electron spin resonance signal, which occurs under annealing process of the samples at T = 570 K. The correlation reasons are a spin-spin coupling between two spin subsystems and time dependent of the Е'γ concentration during annealing process.

Conduction electron spin resonance in AlB2

This work reports on electron spin resonance experiments in oriented single crystals of the hexagonal AlB2 diboride compound (P6/mmm, D16h structure) which display conduction electron spin resonance. The X-band electron spin resonance spectra showed a metallic Dysonian resonance with g-value and intensity independent of temperature. The thermal broadening of the anisotropic electron spin resonance linewidth ΔH tracks the T-dependence of the electrical resistivity below T ≃ 100 K. These results confirm the observation of a conduction electron spin resonance in AlB2 and are discussed in comparison with other boride compounds. Based on our main findings for AlB2 and the calculated electronic structure of similar layered honeycomb-like structures, we conclude that any array of covalent B–B layers potentially results in a conduction electron spin resonance signal. This observation may shed new light on the nature of the non-trivial conduction electron spin resonance-like signals of complex f-electron systems such as β-YbAlB4.

Identifying the electron spin resonance of conduction electrons in alkali doped SWCNTs

AbstractWe study the electron spin resonance (ESR) signal of pristine and potassium doped SWCNTs. We identify signals of a super‐paramagnetic background, a low intensity impurity, and of the conduction electron spin resonance (CESR). The latter only appears upon the alkali atom doping. To identify the CESR signal, we critically assess whether it could come from residual graphitic carbon, which we clearly exclude. We give accurate values for the signal intensities and the corresponding concentration of spins and for the g‐factors. The CESR signal intensity allows to determine the density of states on the SWCNT assembly.

Conduction electron spin resonance of small silver particles

Electron spin resonance (ESR) spectroscopy has been used to study the conduction electron spin resonance (CESR) of small silver particles stabilized in dehydrated Ag-rho zeolite. Silver particles were produced by hydrogen reduction at elevated temperatures and diameter of the stabilized particles was calculated based on the linewidth of CESR signal using Kawabata theory.

In situ conduction ESR and theoretical studies of graphite intercalation by nitric acid

Results of an in situ conduction electron-spin resonance (CESR) study of HNO, molecule intercalation into highly oriented pyrolytic graphite (HOPG) plate with width being comparable with the graphite skin-depth governed by thec-axis conductivity are presented. The changes in the graphite CESR signal line shape, intensity and linewidth and the stepwise changes both of intensity and linewidth of CESR signal of intercalated sample were clearly detected during this reaction. Under the assumption that the graphite CESR signal evolution is caused by the advance of a boundary separating the intercalated and nonintercalated HOPG, the average value of spin reorientation probability during the collision of current carriers with this interface and the diffusion coefficient of nitric acid into the HOPG plate were extracted from experimental data. With the chemical potential versus intercalation time proposed by the authors for the experimental conditions, the stepwise changes of the CESR signal intensity of intercalated sample was calculated theoretically.

Ground state of orthorhombicRbC60:A high-field electron-spin-resonance investigation

We report on electron paramagnetic resonance in the low-temperature phase of orthorhombic ${\mathrm{RbC}}_{60}$ at 94 and 140 GHz microwave frequencies. Below about 25--30 K characteristic features that could be related to antiferromagnetic resonance (AFMR) or alternatively to spin clusters are clearly distinguished from the conduction-electron spin resonance signal above 50 K. The different scenarios, AFMR vs spin glass or spin clusters, are discussed. If the experimental data are interpreted within the AFMR scenario the corresponding spin-flop field can be estimated to be about 0.34 T.

Observation of conduction electron spin resonance in the neodymium cerium copper oxide (Nd1.85Ce0.15CuO4-y) superconductor

Normal and superconducting Nd{sub 2{minus}x}Ce{sub x}CuO{sub 4{minus}y} (x = 0.00, 0.15) compounds have been studied by electron spin resonance (ESR). In contrast to previous reports that the high-temperature superconducting oxocuprate compounds are ESR silent, a conduction ESR (CESR) signal has been observed in the superconducting Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}y} compound. The temperature dependence of the CESR signal intensity, g value, and line width are consistent with a two-dimensional spin structure in Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}y}. A possible reason for the lack of a CESR signal in other high-temperature superconducting systems is that they have more efficient spin-lattice relaxation which is associated with CESR lines too broad to be detected. 14 refs., 4 figs.

Effect of nuclear polarization on the conduction-electron spin resonance in InP

We present conduction-electron spin resonance (CESR) data on n-type InP. Owing to motional narrowing, quite sharp CESR signals have been observed, which allows one to study shifts of the CESR lines as a consequence of both equilibrium and dynamic nuclear polarization of $^{115}\mathrm{In}$ nuclei. The monoexponential recovery of the nuclear polarization to thermal equilibrium after dynamic polarization gives a measure of the $^{115}\mathrm{In}$ relaxation time: ${T}_{1}^{(N)}$=450 s at 3.5 K. Moreover, the $^{115}\mathrm{In}$ nuclear magnetic resonance has been measured by the shift of the CESR signal under additional rf irradiation of the sample.

Evidence for a phase-transition-induced change in the surface spin-flip probability of conduction electrons from CESR on n-irradiated, LIF; its application as an intensity reference

In view of its application as an intensity marker in electron spin resonance, the conduction electron spin resonance signal of Li particles in neutron-irradiated LiF has been analysed regarding its lineshape, linewidth, intensity and spectral composition in the temperature range 4.2<or=T<or=300 K at the X and K bands. While the lineshape is Lorentzian at 300 K, apparently, strong deviations from this shape develop at lower temperatures, without any noticeable change in the g-value or the peak-to-peak linewidth Delta Bpp approximately=0.065 mT; the linewidth, as expected, is found to be dominated by electron-surface scattering. Double numerical integration of the absorption-derivative dPmu a/dB spectra shows the number of spins to be T-independent, as expected from a Pauli-paramagnetic behaviour. Data analysis reveals that, as T decreases, the single Lorentzian line observed at 300 K gradually evolves more and more to a sum of Lorentz lines (likely 2) of all identical g but of different widths 0.065<or= Delta Bpp<or=0.218 mT. This finding has important implications for the use of LiF:Li as an intensity marker, both as regards the Delta Bpp2Y'm method (Y'm being the signal amplitude) of the double integration method to the signal intensity from the dPmu a/dB spectra. The effect arises from a change upon cooling of the spin-flip probability epsilon Li for scattering of conduction electrons at a non-magnetic interface, i.e., Li metal-surrounding; this is tentatively ascribed to the martensitic phase transition in Li.

A conduction electron spin resonance study of interactions in carbon black—polymer composites

Carbon black—polymer composites made either by extrusion or by ultrasonic irradiation and subsequent solvent casting into films gave rise to a conduction electron spin resonance (CESR) signal. This narrow CESR signal with a linewidth (Δ H pp) of 3 G was shown to be equivalent to the signal produced upon electrochemical reduction of the carbon black. The broad CESR signal associated with charge carriers in this black can also be used to probe polymer—carbon black interactions by observing changes in linewidth. Inclusion of a surfactant in the composite during extrusion results in its adsorption onto the carbon black. This leads to a reduction in the narrow CESR signal and an increase in the Δ H pp of the broad CESR signal.

Radiation damage in neutron transmutation-doped silicon. I. Electron paramagnetic resonance study

The removal of the radiation damage in neutron transmutation-doped silicon during the isochronal annealing from a temperature of 423–1223 K has been monitored by electron paramagnetic resonance spectroscopy. The dominant defect centers have been identified to be P1, A2, A4, A8, and A11. Complete decay of all the defect centers has been found to take place on annealing at 923 K, where a complete recovery of conduction electron spin resonance signal also takes place.

Fermi-surface structure effects revealed by the observation of conduction-electron-spin resonance in Zn

The first observation of conduction-electron-spin resonance (CESR) in polycrystalline highpurity Zn in the temperature range between 4.8 and 35 K is reported. The observed $g$ value equals 2.0033 \ifmmode\pm\else\textpm\fi{} 0.0005, and the linewidth above 11 K increases with temperature, as expected from the normal electron-phonon interaction. The signal is explained as being due to the "lens" part of the Zn Fermi surface, advancing herewith a new type of interpretation of CESR data. The usual CESR signal coming from the main part of the Fermi surface is believed to be broadened beyond the detection limit due to magnetic breakdown effects interplaying with the complex Fermi surface. Similar features in Mg are discussed.

ESR Studies on the Reduction Process of Silver Zeolites

AbstractIt is shown by in situ ESR studies that H2 reduction of dehydrated AgA‐ and AgX‐zeolites proceeds via intermediate formation of Agn+6 (n &lt; 6) clusters, located inside the cubooctahedral sodalite cages. On further reduction, submicroscopic Ag crystals (&lt;5 nm) are formed, resulting in a conduction electron spin resonance signal. At higher temperatures (T &gt; 200°C) crystal growth leads to larger crystallites (10–50 nm) as indicated by x‐ray line broadening.