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Results for “ELECTRON SPIN RESONANCE”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Magnetism of gold nanorods probed using electron spin resonance

Electron spin resonance (ESR) spectroscopy has been performed for gold nanorods (AuNRs) of four different sizes covered with a diamagnetic stabilizing component, cetyltrimethylammonium bromide. ESR signals were detected in AuNRs except the largest one. Two smallest AuNRs showed an abrupt change in the temperature dependence of resonance field and line width at around 60 K, indicating ferromagnetic phase transition. In medium-size AuNRs, the resonance with a large shift was observed below 100 K. The resonance field shifts at the lowest temperature exhibit systematic variation with the system size, which is explained by considering magnetic anisotropy for the ferromagnetic resonance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation

Electronic spin transport properties of graphene nanoribbons (GNRs) are influenced by the presence of adatoms, adsorbates and edge functionalization. To improve the understanding of the factors that influence the spin properties of GNRs, local (element) spin-sensitive techniques such as electron spin resonance (ESR) spectroscopy are important for spintronics applications. Here, we present results of multi-frequency continuous wave (CW), pulse and hyperfine sublevel correlation (HYSCORE) ESR spectroscopy measurements performed on oxidatively unzipped graphene nanoribbons (GNRs), which were subsequently chemically converted (CCGNRs) with hydrazine. ESR spectra at 336 GHz reveal an isotropic ESR signal from the CCGNRs, of which the temperature dependence of its line width indicates the presence of localized unpaired electronic states. Upon functionalization of CCGNRs with 4-nitrobenzene diazonium tetrafluoroborate, the ESR signal is found to be 2 times narrower than that of pristine ribbons. NH{sub 3} adsorption/desorption on CCGNRs is shown to narrow the signal, while retaining the signal intensity and g value. The electron spin-spin relaxation process at 10 K is found to be characterized by slow (163 ns) and fast (39 ns) components. HYSCORE ESR data demonstrate the explicit presence of protons and {sup 13}C atoms. With the provided identification of intrinsic point magnetic defects such as proton and {sup 13}C has been reported, which are roadblocks to spin travel in graphene-based materials, this work could help in advancing the present fundamental understanding on the edge-spin (or magnetic)-based transport properties of CCGNRs.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Dramatic enhancement of fullerene anion formation in polymer solar cells by thermal annealing: Direct observation by electron spin resonance

Using electron spin resonance (ESR), we clarified the origin of the efficiency degradation of polymer solar cells containing a lithium-fluoride (LiF) buffer layer created by a thermal annealing process after the deposition of an Al electrode (post-annealing). The device structure was indium-tin-oxide/ poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/poly (3-hexylthiophene):phenyl-C{sub 61}-butyric acid methyl ester (P3HT:PCBM)/LiF/Al. Three samples consisting of quartz/P3HT:PCBM/LiF/Al, quartz/P3HT:PCBM/Al, and quartz/PCBM/LiF/Al were investigated and compared. A clear ESR signal from radical anions on the PCBM was observed after LiF/Al was deposited onto a P3HT:PCBM layer because of charge transfer at the interface between the PCBM and the LiF/Al, which indicated the formation of PCBM{sup −}Li{sup +} complexes. The number of radical anions on the PCBM was enhanced remarkably by the post-annealing process; this enhancement was caused by the surface segregation of PCBM and by the dissociation of LiF at the Al interface by the post-annealing process. The formation of a greater number of anions enhanced the electron scattering, decreased the electron-transport properties of the PCBM molecules, and caused an energy-level shift at the interface. These effects led to degradation in the device performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Dual nature of 3 d electrons in YbT 2 Zn 20 (T = Co; Fe) evidenced by electron spin resonance

The electron spin resonance experiments were carried out in the single crystals YbFe 2 Zn 20 . The observed spin dynamics is compared with that in YbCo 2 Zn 20 and Yb 2 Co 12 P 7 as well as with the data of inelastic neutron scattering and electronic band structure calculations. Our results provide direct evidence that 3d electrons are itinerant in YbFe 2 Zn 20 and localized in YbCo 2 Zn 20 . Possible connection between spin paramagnetism of dense heavy fermion systems, quantum criticality effects, and ESR spectra is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

In situ electrochemical-electron spin resonance investigations of multi-electron redox reaction for organic radical cathodes

Organic radical batteries (ORBs) bearing robust radical polymers as energy storage species, are emerging promisingly with durable high energy and power characteristics by unique tunable redox properties. Here we report the development and application of in situ electrochemical-electron spin resonance (ESR) methodologies to identify the charge transfer mechanism of Poly(2,2,6,6- tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) based organic radical composite cathodes in the charge-discharge process of lithium half cells. The in situ experiments allow each electrochemical state to be associated with the chemical state (or environment) of the radical species upon the cell cycling. In situ ESR spectra of the composite cathode demonstrate a two-electron redox reaction of PTMA. Moreover, two different local environments of radical species are found in the composite electrode that includes both concentrated and isolated radicals. These two types of radicals show similarities during the redox reaction process while behave quite differently in the non-faradic reaction of ion sorption/desorption on the electrode surface.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Instrument for in-situ orientation of superconducting thin-film resonators used for electron-spin resonance experiments

When used in electron-spin resonance measurements, superconducting thin-film resonators must be precisely oriented relative to the external magnetic field in order to prevent the trapping of magnetic flux and the associated degradation of resonator performance. We present a compact design solution for this problem that allows in-situ control of the orientation of the resonator at cryogenic temperatures. Tests of the apparatus show that when proper alignment is achieved, there is almost no hysteresis in the field dependence of the resonant frequency.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Antiferromagnetic ordering in spin-chain multiferroic Gd{sub 2}BaNiO{sub 5} studied by electronic spin resonance

High-field electron spin resonance (ESR) has been employed to study the antiferromagnetic (AFM) ordering state (T < T{sub N} = 55 K) of spin-chain multiferroic Gd{sub 2}BaNiO{sub 5}. The spin reorientation at T{sub SR} = 24 K is well characterized by the temperature-dependent ESR spectra. The magnetization data evidence a field-induced spin-flop transition at 2 K. The frequency-field relationship of the ESR data can be explained by conventional AFM resonance theory with uniaxial anisotropy, in good agreement with magnetization data. Related discussion on zero-field spin gap is presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Evolution of the 4f electron localization from YbRh{sub 2}Si{sub 2} to YbRh{sub 2}Pb studied by electron spin resonance

We report on electron spin resonance (ESR) experiments on the Heusler alloy YbRh{sub 2}Pb and compare its spin dynamics with that of several other Yb-based intermetallics. A detailed analysis of the derived ESR parameters indicates the extremely weak hybridization, more localized distribution of the 4f states, and a smaller RKKY interaction in YbRh{sub 2}Pb. These findings reveal the important interplay between hybridization effects, chemical substitution, and crystalline electric field interactions that determines the ground state properties of strongly correlated electron systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Hexagonal CoO nanoparticles as studied by electron spin resonance

We report the electron spin resonance (ESR) results of hexagonal CoO nanoparticles those are different in average size. The temperature evolution of ESR spectra was found to be complicated in nature. The anomalous ESR behaviour is ascribed to (i) uncompensated magnetic sublattice, (ii) magnetic anisotropy of nanoparticles, and (iii) spatial distribution of the anisotropy axis with respect to the magnetic field. Anomalous changes of resonance field and linewidth were observed near the Néel temperature, T{sub N}. According to the temperature dependence of ESR intensity, the T{sub N} values are found to be 225, 255, and 285 K for hexagonal CoO nanoparticles with sizes of 38, 49, and 67 nm, respectively. We found that the size dependence of T{sub N} fits well with the Boltzmann curve.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1973

Metallic Fe phases in Apollo 16 fines - Their origin and characteristics as revealed by electron spin resonance studies

The intense electron spin resonance (ESR) signals detected in the Apollo 16 fines from three sites (61141,4, Station 1; 64501,22, South Ray Crater; 67601,20, North Ray Crater) are found to be essentially similar in g-value, in lineshape asymmetry and in temperature dependence to those previously observed for the Apollo 11-15 fines. On the basis of these similarities, it is concluded that these ESR signals like those detected in the Apollo 11-15 fines are principally ferromagnetic in nature arising from metallic Fe phases having the body-centered cubic structure, and not from hematite, magnetite, or any other ferric oxides. It is shown that a quantitative correlation exists between the ESR linewidth observed for the Apollo 11-16 fines and their average Ni contents in the metallic Fe phases as determined by other means. A common source of meteoritic origin is indicated for the metallic Fe phases of these samples.

Tsay, F.-D.↗
DOE OSTI2015

Induction-detection electron spin resonance with spin sensitivity of a few tens of spins

Electron spin resonance (ESR) is a spectroscopic method that addresses electrons in paramagnetic materials directly through their spin properties. ESR has many applications, ranging from semiconductor characterization to structural biology and even quantum computing. Although it is very powerful and informative, ESR traditionally suffers from low sensitivity, requiring many millions of spins to get a measureable signal with commercial systems using the Faraday induction-detection principle. In view of this disadvantage, significant efforts were made recently to develop alternative detection schemes based, for example, on force, optical, or electrical detection of spins, all of which can reach single electron spin sensitivity. This sensitivity, however, comes at the price of limited applicability and usefulness with regard to real scientific and technological issues facing modern ESR which are currently dealt with conventional induction-detection ESR on a daily basis. Here, we present the most sensitive experimental induction-detection ESR setup and results ever recorded that can detect the signal from just a few tens of spins. They were achieved thanks to the development of an ultra-miniature micrometer-sized microwave resonator that was operated at ∼34 GHz at cryogenic temperatures in conjunction with a unique cryogenically cooled low noise amplifier. The test sample used was isotopically enriched phosphorus-doped silicon, which is of significant relevance to spin-based quantum computing. The sensitivity was experimentally verified with the aid of a unique high-resolution ESR imaging approach. These results represent a paradigm shift with respect to the capabilities and possible applications of induction-detection-based ESR spectroscopy and imaging.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Electron spin resonance spectroscopy with femtoliter detection volume

We report electron spin resonance measurements of donors in silicon at millikelvin temperatures using a superconducting LC planar micro-resonator and a Josephson parametric amplifier. The resonator includes a nanowire inductor, defining a femtoliter detection volume. Due to strain in the substrate, the donor resonance lines are heavily broadened. In this work, single-spin to photon coupling strengths up to ~ 3 kHz are observed. The single shot sensitivity is 120 ± 24 spins/Hahn echo, corresponding to ≈ 12 ± 3 spins / Hz for repeated acquisition.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1973

Observation of electron spin resonance of negative ions in liquid helium

Electron spin resonance signals of negative ions in liquid helium were observed. The line width and g-value were measured. Electrons injected into helium by field emission from ferromagnetic tips are shown to be polarized. A new technique for the measurement of electron spin polarization is presented.

Reichert, J. F.↗
DOE OSTI2016

Electron spin resonance (ESR) of magnetic sublattices in Sc-substituted barium hexaferrite

The partial substitution of Fe{sup 3+} by Sc{sup 3+} in barium hexaferrite has shown to be an effective method to tailor anisotropy for many novel microwave applications. Some basic studies have revealed that this substitution leads to unusual interactions among the magnetic sublattices of the ferrite. In order to investigate these interactions, samples with formula BaSc{sub x}Fe{sub 12-x}O{sub 19} (1 ≤x ≤ 2) were prepared by sintering (1300°C, 6h). After structural characterization by x-ray diffraction, their ferromagnetic resonance spectra were measured in the X-band (9.4 GHz), in the 100-500 K temperature range. For x = 2, a single, broad resonance peak was observed at the low temperatures (103 K), exhibiting a progressive splitting into two peaks for increasing T, to finally coalesce again into a single (paramagnetic) narrow peak at 473 K. These results are interpreted in terms of a substitution of Fe{sup 3+} by Sc{sup 3+} ions in the 4f{sub vi} and 2b sublattices; the diamagnetic cations disrupt the superexchange interactions and produce a splitting of the 12k sublattice (which interacts directly with the 4f{sub vi} sublattice) into two sublattices with different canting angles, and different thermal dependence. As a result, the fraction of the 12k sublattices that are nearest neighbours of substituted 4f{sub vi} sites can behave as an independent sublattice for some temperature ranges. A similar behavior is observed for all the compositions with varying degrees of amplitude, but it is more evident for x = 2. A deconvolution of peaks has been attempted, in order to shed more light into this behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Conduction-Electron Spin Resonance in HgSe Crystals

Samples of a gapless HgSe semiconductor with different iron impurity concentrations are investigated. HgSe:Fe samples are examined by the electron-spin-resonance technique. Multiple resonance lines caused by unpaired spins of different origins are analyzed. The properties of electrons localized at shallow impurities are described using a hydrogen-like model. The effect of an internal field on the resonance lines is established. It is found that the conduction of HgSe is not only nonparabolic, but also nonspherical.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Gd{sup 3+} electron spin resonance spectroscopy on LaO{sub 1-x}F{sub x}FeAs superconductors

We report an electron spin resonance (ESR) spectroscopy study on polycrystalline samples of the LaO{sub 1-x}F{sub x}FeAs (x = 0 and 0.1) compound with small levels of Gd doping (2% and 5%). The Gd ESR signal is found to be sensitive to the magnetic phase transition from the paramagnetic to the spin density wave (SDW) state occurring in the parent LaO{sub 1-x}F{sub x}FeAs compounds at T{sub SDW} {approx} 130 K. Interestingly, the analysis of the low-temperature ESR spectra of the c-axis oriented Gd{sub 1-y}La{sub y}OFeAs samples gives evidence for the magnetically nonequivalent Gd sites and also for sites having a different local charge environment. The analysis of the temperature dependence of the ESR linewidths gives evidence for a coupling of the localized 4f electrons of Gd to the conduction electrons in the FeAs layers. The ESR data reveal that the fluorine substitution, which provides electron doping, suppresses the SDW order and enhances the density of states in the electronic bands stemming from the xz and yz orbital states of Fe to which the 4f electrons are most strongly coupled.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Temperature dependent behavior of localized and delocalized electrons in nitrogen-doped 6H SiC crystals as studied by electron spin resonance

We have studied the temperature behavior of the electron spin resonance (ESR) spectra of nitrogen (N) donors in n-type 6H SiC crystals grown by Lely and sublimation sandwich methods (SSM) with donor concentration of 10{sup 17 }cm{sup −3} at T = 60–150 K. A broad signal in the ESR spectrum was observed at T ≥ 80 K with Lorentzian lineshape and g{sub ||} = 2.0043(3), g{sub ⊥} = 2.0030(3), which was previously assigned in the literature to the N donors in the 1s(E) excited state. Based on the analysis of the ESR lineshape, linewidth and g-tensor we attribute this signal to the conduction electrons (CE). The emergence of the CE ESR signal at T > 80 K was explained by the ionization of electrons from the 1s(A{sub 1}) ground and 1s(E) excited states of N donors to the conduction band while the observed reduction of the hyperfine (hf) splitting for the N{sub k1,k2} donors with the temperature increase is attributed to the motional narrowing effect of the hf splitting. The temperature dependence of CE ESR linewidth is described by an exponential law (Orbach process) with the activation energy corresponding to the energy separation between 1s(A{sub 1}) and 1s(E) energy levels for N residing at quasi-cubic sites (N{sub k1,k2}). The theoretical analysis of the temperature dependence of microwave conductivity measured by the contact-free method shows that due to the different position of the Fermi level in two samples the ionization of free electrons occurs from the energy levels of N{sub k1,k2} donors in Lely grown samples and from the energy level of N{sub h} residing at hexagonal position in 6H SiC grown by SSM.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗