Dysonian Line Shape Research Articles

3D Variable Range Hopping Electrical Conduction of a Carbon from Polyaniline Vapor

Carbon with a metallic reflection was prepared from polyaniline (PANI) vapor deposited on the inner quartz wall of a furnace. Electron probe microanalyzer analysis proved that the resultant contained carbon, oxygen, nitrogen, and sulfur atoms. A Dysonian line shape with paramagnetic properties was observed for the resulting carbon from PANI in the electron spin-resonance spectroscopy measurement. The resistance vs. temperature curve of the carbon indicated semiconductor-insulator properties in a low-temperature range. Electrical conduction in the carbon was carried out with 3D variable range hopping.

Electron spin dynamics in sucrose-derived luminescent carbon dot-silica nanocomposites

In the present work, a bottom-up approach to synthesize luminescent carbon dot-silica (CDs@SiO2) nanocomposites from the sucrose precursor was utilized. The sucrose concentration and thermal treatment effect on electron spin dynamics in CDs@SiO2 nanocomposites was investigated by electron spin resonance (ESR) technique. A single ESR line resulting from exchange interaction between localized and non-localized electrons was observed. The non-localized electrons were related to carbon-related radicals in the sp3-hybridized state, while the carbon dots (CDs) act as localized electrons. The observed narrowing of the exchange ESR line with temperature rise was explained by a combination of Anderson's spin-exchange motional narrowing and a hopping wave function. The high conductivity of the material is evidenced by the Dysonian lineshape of the ESR signal. The relation between CDs size and conductivity of the CDs@SiO2 nanocomposites was found. The metallic character of the CDs@SiO2 conductivity was explained by the quantum size effect that occurred due to the reaggregation of the CDs. It was concluded that the previously observed shift of photoluminescence (PL) band and further quenching of PL with the increase of sucrose concentration in CDs@SiO2 is caused by the quantum size effect.

Complex magnetic behavior along the GdIn(NixCu1-x)4 (0.00 ≤ x ≤ 1.00) series of compounds

In this work, structural, magnetic, and local properties of GdIn(NixCu1−x)4 (0.00 ≤ x ≤ 1.00) samples synthesized via the flux method are investigated by means of X-ray, magnetization, specific heat, and electron spin resonance measurements. The analysis of X-ray powder diffraction data taken at room temperature reveals that all samples belong to the cubic space group (Cl5b-type structure) with lattice parameters, a, ranging from 7.08 < a < 7.23 Å. Interestingly, the analysis of both T-dependence magnetic susceptibility and MvsH loops indicates a gradual transition from antiferromagnetic to ferromagnetic ground states as a function of the Ni-doping. The transition temperatures are confirmed via specific heat measurements. Finally, electron spin resonance data taken in the temperature range of 100 ≤ T ≤ 300 K show a single Dysonian line shape, which is characteristic of a metallic environment. A nearly T-independent g-value was observed and the value was concentration independent. Besides, the doped samples show an increase of the residual linewidth, which can be linked with the chemical disorder introduced by the Ni-doping. Our results are discussed considering the bottleneck and multiple band effects on the Gd3+ spin dynamics in this series and their implication in the magnetic frustration observed in these materials.

Diffusive-like effects and possible non trivial local topology on the half-Heusler YPdBi compound

The non-ambiguous experimental identification of topological states of matter is one of the main interesting problems regarding this new quantum state of matter. In particular, the half-Heusler family RMT (R = rare-earth, T = Pd, Pt or Au and T = Bi, Sb, Pb or Sn) could be a useful platform to explore these states due to their cubic symmetry and the topological properties tunable via their unit cell volume and/or the nuclear charges of the M and T atoms. In this work, we report electron spin resonance (ESR) and complementary macroscopic measurements in the Nd3 + -doped putative topologically trivial semimetal YPdBi. Following the Nd3 + ESR lineshape as a function of microwave power, size of the particle and temperature, we have been able to observe an evolution from a Dysonian lineshape to a diffusive-like lineshape. Furthermore, the Nd3 + ESR intensity saturation is concentration dependent, which could be due to a phonon-bottleneck process. Comparing these results with the Nd3 + -doped YPtBi, we discuss a possible scenario in which the Nd3 + ions could locally tune the topological properties of the system.

3D printed sample holder for in-operando EPR spectroscopy on high temperature polymer electrolyte fuel cells

Electrochemical cells contain electrically conductive components, which causes various problems if such a cell is analyzed during operation in an EPR resonator. The optimum cell design strongly depends on the application and it is necessary to make certain compromises that need to be individually arranged. Rapid prototyping presents a straightforward option to implement a variable cell design that can be easily adapted to changing requirements. In this communication, it is demonstrated that sample containers produced by 3D printing are suitable for EPR applications, with a particular emphasis on electrochemical applications. The housing of a high temperature polymer electrolyte fuel cell (HT-PEFC) with a phosphoric acid doped polybenzimidazole membrane was prepared from polycarbonate by 3D printing. Using a custom glass Dewar, this fuel cell could be operated at temperatures up to 140°C in a standard EPR cavity. The carbon-based gas diffusion layer showed an EPR signal with a characteristic Dysonian line shape, whose evolution could be monitored in-operando in a non-invasive manner.

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.

The electron spin resonance study of heavily nitrogen doped 6H SiC crystals

The magnetic and electronic properties of heavily doped n-type 6H SiC samples with a nitrogen concentration of 1019 and 4 × 1019 cm−3 were studied with electron spin resonance (ESR) at 5–150 K. The observed ESR line with a Dysonian lineshape was attributed to the conduction electrons (CE). The CE ESR (CESR) line was fitted by Lorentzian (insulating phase) (T < 40 K) and by Dysonian lineshape (metallic phase) above 40 K, demonstrating that Mott insulator-metal (IM) transition takes place at ∼40 K, accompanied by significant change in the microwave conductivity. The temperature dependence of CESR linewidth follows the linear Korringa law below 40 K, caused by the coupling of the localized electrons (LE) and CE, and is described by the exponential law above 40 K related to the direct relaxation of the LE magnetic moments via excited levels driven by the exchange interaction of LE with CE. The g-factor of the CESR line (g‖ = 2.0047(3), g⊥ = 2.0034(3)) is governed by the coupling of the LE of nitrogen donors at hexagonal and quasi-cubic sites with the CE. The sharp drop in CESR line intensity (25–30 K) was explained by the formation of antiferromagnetic ordering in the spin system close to the IM transition. The second broad ESR line overlapped with CESR signal (5–25 K) was attributed to the exchange line caused by the hopping motion of electrons between occupied and non-occupied positions of the nitrogen donors. Two mechanisms of conduction, hopping and band conduction, were distinguished in the range of T = 10–25 K and T > 50 K, respectively.

Correlated spin systems in undoped CdSe quantum dots

The electronic properties of quantum dots have been studied extensively, and recent studies have explored various dopants that can alter electronic properties in quantum dots. Yet, we have found that impurities on the surface of nanometer-scale CdSe materials can also affect electronic properties. Specifically, nitrogen-based impurities on the surface of nanometer-scale CdSe materials (from ~4 to 15 nm) interact with the CdSe conduction electrons to yield an anti-ferromagnetic EPR signal at a high resonance field (g ~ 0.56) that has an inverse Dysonian lineshape. However, bulk CdSe particles do not show the same types of EPR signals. This paper will discuss these observations, explain the underlying phenomena, and discuss implications for future research.

Spin relaxation times of single-wall carbon nanotubes

We have measured temperature ($T$)- and power-dependent electron spin resonance in bulk single-wall carbon nanotubes to determine both the spin-lattice and the spin-spin relaxation times, ${T}_{1}$ and ${T}_{2}$. We observe that ${T}_{1}^{\ensuremath{-}1}$ increases linearly with $T$ from 4 K to 100 K, whereas ${T}_{2}^{\ensuremath{-}1}$ decreases by over a factor of two when $T$ is increased from 3 K to 300 K. We interpret the ${T}_{1}^{\ensuremath{-}1}\ensuremath{\propto}T$ trend as spin-lattice relaxation via interaction with conduction electrons (Korringa law) and the decreasing $T$ dependence of ${T}_{2}^{\ensuremath{-}1}$ as motional narrowing. By analyzing the latter, we find the spin hopping frequency to be 285 GHz. Last, we show that the Dysonian line shape asymmetry follows a three-dimensional variable-range hopping behavior from 3 K to 20 K; from this scaling relation, we extract a localization length of the hopping spins to be $\ensuremath{\sim}$100 nm.

A highly conducting organic metal derived from an organic-transistor material: benzothienobenzothiophene

BTBT ([1]benzothieno[3,2-b][1]benzothiophene) is an organic semiconductor that realizes high mobility in organic transistors. Here we report that the charge-transfer (CT) salt, (BTBT)2PF6, shows a high room-temperature conductivity of 1500 S cm(-1). This compound exhibits a resistivity jump around 150 K, but when it is covered with Apiezon N grease the resistivity jump is suppressed, and the metallic conductivity is maintained down to 60 K. Owing to the very high conductivity, the ESR signal shows a significantly asymmetric Dysonian lineshape (A/B ≅ 3) even at room temperature. Since most organic conductors are based on strong electron donors, it is remarkable that such a weak electron donor as BTBT realizes a stable and highly conducting organic metal.

Electrical transport and EPR investigations: A comparative study for d.c. conduction mechanism in monovalent and multivalent ions doped polyaniline

A detailed comparative study of electron paramagnetic resonance (EPR) in conjunction with d.c. electrical conductivity has been undertaken to know about the charge transport mechanism in polyaniline (PANI) doped with monovalent and multivalent protonic acids. This work is in continuation of our previous work for further understanding the conduction mechanism in conducting polymers. The results reveal that the polarons and bipolarons are the main charge carriers formed during doping process and these cause increase in electrical conductivity not only by increase in their concentration but also because of their enhanced mobility due to increased inter-chain transport in polyaniline at high doping levels. EPR line asymmetry having Dysonian line shape for highly doped samples shows a marked deviation of amplitudes A/B ratio from values close to one to much high values as usually observed in metals, thereby support the idea of high conductivity at higher doping levels. The nature of dopant ions and their doping levels control the charge carriers concentration as well as electrical conductivity of polyaniline. The electrical conductivity has also been studied as a function of temperature to know the thermally assisted transport process of these charge carriers at different doping levels which has been found to follow the Mott’s variable range hopping (VRH) conduction model for all the three dopants used. The charge carriers show a change over from 3D VRH to quasi 1D VRH hopping process for multivalent ions at higher doping levels whereas 1D VRH has been followed by monovalent ion for full doping range. These studies collectively give evidence of inter-chain percolation at higher doping levels causing increase in effective mobility of the charge carriers which mainly seems to govern the electrical conduction behaviour in this system.

Density of states deduced from ESR measurements on low‐dimensional nanostructures; benchmarks to identify the ESR signals of graphene and SWCNTs

AbstractElectron spin resonance (ESR) spectroscopy is an important tool to characterize the ground state of conduction electrons and to measure their spin‐relaxation times. Observing ESR of the itinerant electrons is thus of great importance in graphene and in single‐wall carbon nanotubes. Often, the identification of CESR signal is based on two facts: the apparent asymmetry of the ESR signal (known as a Dysonian lineshape) and on the temperature independence of the ESR signal intensity. We argue that these are insufficient as benchmarks and instead the ESR signal intensity (when calibrated against an intensity reference) yields an accurate characterization. We detail the method to obtain the density of states from an ESR signal, which can be compared with theoretical estimates. We demonstrate the success of the method for K doped graphite powder. We give a benchmark for the observation of ESR in graphene.

Electron-Spin Resonance of a La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ Slab

We have studied electron-spin resonance (ESR) spectra of a La0.7Sr0.3MnO3 slab. Experimental results reveal that ESR spectra in the ferromagnetic (FM) region are followed with a broadly resonant mode as θ = 90°, but several modes as θ = 0°. Their spectral parameters depend strongly on θ. When keeping θ = 0° and measuring the temperature dependence of ESR spectra, it is found that several resonant modes in the FM region become a single mode in the Dysonian line-shape at temperatures T >; Tmin ≈ 1.1 TC. At Tmin, the spectral linewidth reaches to a minimum value of ΔHmin= 283 Oe. Temperature dependences of the EPR intensity above Tmin obey a function I(T) = Io exp(Ea/ kB T). Having based on the relation of I(T) ∝ χ(T) = 1/(T-Θ) , we obtained the Curie-Weiss temperature Θ to be 376 K. If using a simple relation of g = hν/ μB Hr (Hr is the resonant position, and μB is the Bohr magneton), we have found that the effective Lande factor g increases from 1.91 (around Tmin) to ~ 1.98 (at 473 K) close to the value of g = 2.0 for spin-spin interactions of Mn ions. This could be due to the additional presence of magnetic interactions, besides spin-spin interactions, such as interactions between FM clusters and/or spin-orbital coupling. Interestingly, despite the sample in the PM regime, the spectral parameters depend on the angle θ. This is assigned to an anisotropic field related to Mn 3+-Mn 4 + FM clusters persisting above Tmin. At 470 K, the anisotropy constant obtained is Ku ≈ 57 erg/cm 3, much smaller than that in the FM region.

EPR study of conduction electrons in heavily doped n-type 4H SiC

The magnetic properties of conduction electrons (CE) in heavily doped n-type 4H SiC have been studied with electron paramagnetic resonance (EPR) in the temperature interval from 7 to 140 K. An EPR line with “Dyson lineshape” was observed in 4H SiC wafers with (ND–NA) ≈ 1019 cm−3. The EPR line is composed of two overlapping lines with Lorentzian and Dysonian lineshape, which are responsible for the localized and delocalized spin systems attributed to electrons localized on the nitrogen donors (LE) and CE, respectively. The Dysonian line is characterized by an asymmetry parameter R. The coupling between the two spin systems, which are characterized by S = 1/2 is realized via an exchange interaction of CE with the LE. As a result the g-factor of the Dysonian spectral line is governed by an exchange interaction between LE and CE and was evaluated as g|| = 2.0045, g⟂ = 2.0003. The temperature dependence of the integral intensity of the CE EPR signal is described by the sum of Curie–Weiss and Pauli paramagnetism. The Curie-like contribution arises from unpaired spins in the impurity band of heavily doped 4H SiC, while a Pauli-like contribution that becomes noticeable at T > 80 K indicates the presence of the CE in the conduction band. From the analysis of the temperature dependence of R(T) and the linewidth ΔH(T) of the CE EPR signal the activation energy of the CE into the conduction band was estimated to be 39.4 meV. The obtained value of the activation energy coincides with that for nitrogen donors forming an impurity band in heavily doped n-type 4H SiC. Thus, the temperature behavior of the CE spin system in highly doped 4H SiC can be interpreted in terms of electrons that are freely moving over the impurity and conduction band. The CE present in the impurity band are strongly coupled with LE by cross-relaxation processes.

Strong reduction of the Korringa relaxation in the spin-density wave regime ofEuFe2As2observed by electron spin resonance

Electron spin resonance measurements in ${\text{EuFe}}_{2}{\text{As}}_{2}$ single crystals revealed an absorption spectrum of a single resonance with Dysonian line shape. Above the spin-density wave (SDW) transition at ${T}_{\text{SDW}}=190\text{ }\text{K}$ the spectra are isotropic and the Eu spins relax via the conduction electrons resulting in a Korringa-type increase in the linewidth. Below ${T}_{\text{SDW}}$, a distinct anisotropy develops and the relaxation behavior of the Eu spins changes drastically into one with characteristic properties of a magnetic insulating system, where dipolar and crystal-field interactions dominate. This indicates a spatial confinement of the conduction electrons to the FeAs layers in the SDW state.

Spin Resonance Absorption in a 2D Electron Gas

We analyze the power absorption at electron spin resonance excited by the Bychkov{Rashba spin{orbit fleld in a 2D electron gas. We show that, as long as the absorbed power is dissipated by the usual spin lattice relaxation mechanisms, the resonance line shape is expected to be of pure absorption type, i.e., it can be described by the imaginary part of the dynamic magnetic susceptibility. Therefore, the Dysonian line shape observed in ESR of 2D electron gas cannot result from this type of the resonance signal.

Electron spin resonance in iron-substituted manganites La 0.67Ca 0.33Mn 1− xFe xO 3

We report electron spin resonance (ESR) measurements on collosal magnetoresistive manganites La 0.67Ca 0.33Mn 1− x Fe x O 3 with x=0, 0.01, 0.03, 0.06, 0.10 and 0.15, as well as on LaMnO 3 and CaMnO 3, in the vicinity of the magnetic transition temperatures T C. ESR lines were fitted by Dysonian line shape. Temperature dependences of the linewidths exhibited a minimum value at T *≅1.25 T C followed by an increase of the width. We concluded that the ferromagnetic metallic clusters, exhibiting the double exchange interaction between Mn 3+–Mn 4+ ions, play a dominant role in the resonance absorption.

ESR Study on YBiPt compound doped by Er 3+ and Gd 3+

The compound YBiPt doped by Er and Gd has been studied by ESR technique in the X and Q-bands between 4 and 300 K. Two anisotropic lines with hyperfine peaks due to the interaction between electronic and nuclear spins of 167Er 3+ (I= 7 2 ) isotope have been observed below 30 K. Dysonian line shape of the Er and Gd ESR signals shows a metallic character of the conductivity in studied samples as well. Computer modeling has shown that these lines belong to the two allowed transitions in the quadruplet ground state of Er +3 ions in the ligand crystal field of cubic symmetry. The values of crystal field parameters B 4=−5.68×10 −4 cm −1 and B 6=−6.64×10 −6 cm −1 have been extracted. An additional isotropic line with g=1.99 observed in both frequency bands has been attributed to the Gd impurities. The temperature dependence of peak-to-peak linewidth of Gd 3+ signal has been well described by the Korringa relaxation of Gd magnetic moments to the itinerant electrons, d Hpp= a+ bT. The value of exchange constant J sf have been estimated from the Korringa slope of b=0.12 Oe/K. The intensity of Gd 3+ signal, which obeys the Curie's law for paramagnetic ions at lowest temperatures, deviates from this law at temperatures higher than 140 K.

ESR studies on Er3+‐doped YBiPt compound

AbstractThe semi‐metallic cubic compound YBiPt doped by Er3+ (4f11) has been studied by ESR technique between 4 and 300 K. X‐band and Q‐band measurements have been performed. The angular dependence of the ESR spectra on the crystal orientation with respect to the static magnetic field has been measured. Two anisotropic lines with hyperfine peaks coming from the interaction between electronic and nuclear spins of 167Er3+ (I = 7/2) isotopes have been observed below 30 K in the spectra. Computer modeling showed that these lines are the ESR signals from the quadruplet ground state of Er3+ ions in the cubic crystal field. The values of crystal field parameters B4 = –5.68 × 10–4 cm–1 and B6 = –6.64 × 10–6 cm–1 have been extracted. Also an isotropic line near g = 2 have been observed in both frequency bands. Dysonian lineshape of the spectra components due to the skin‐depth effect shows the conducting property of the sample under study. The temperature dependence of the spectra intensity obeys the well‐known Curie law for paramagnetism arising from the unpaired electrons of Er3+ ion.

ESR of different Gd 3+ sites in CaB 6

The environment of Gd 3+ (4f 7, S= 7 2 ) ions in single crystals of Ca l− x Gd x B 6 (0.0001⩽ x⩽0.01) is studied by electron spin resonance (ESR). The spectra for x⩽0.001 show a split spectrum due to cubic crystal field effects (CFE). The line shape of each fine structure line is Lorentzian, indicating an insulating environment for the Gd 3+ ions. For 0.003⩽ x⩽0.01, the spectra show a single resonance ( g≈1.992(4), Δ H l/2 ≈60 Oe) with no CFE and Dysonian line shape indicating metallic environment for the Gd 3+ ions. For intermediate concentrations, a coexistence of spectra corresponding to insulating and metallic regions is observed. Most of the measured samples show the weak ferromagnetism (WF) as reported for Ca 0.995La 0.005B 6, but, surprisingly, this WF has no effect in our ESR spectra either for metallic or insulating environments. This result suggests that the WF in these systems might be isolated in clusters (defect-rich regions) and its relationship with metallicity is nontrivial.