Hyperfine Interaction Of Electron Research Articles

Density functional theory study of Al, Ga and in impurities in diamond

As a consequence of its high atomic number density, diamond can incorporate a relatively limited range of impurities as distributed point-defects, chiefly N, B and H. A few other species can be grown-in, and other impurity species incorporated via implantation and annealing. For applications including electronic, electrical and quantum devices, the presence of states deep within the wide band-gap is of importance, and the list of potential colour centres available for exploitation continues to grow. Although B can be grown into diamond at high concentration, study of other group-13 elements is rather limited. In this paper we present the results of modelling of Al, Ga and In. We find all species readily form complexes with vacancies, and exhibit electronic structures that parallel those of the SiV complex. We report electronic structures, electrical levels, optical transitions and hyperfine interactions of the colour centres, as well as reflect upon the thermodynamics of the complexes. We suggest that co-implanting group-13 elements with nitrogen would give rise to the defect charge states with potential for quantum applications.

EPR of LiNaGe4O9:Mn crystal

EPR spectra of manganese ions were studied in lithium-sodium tetragermanate LiNaGe4O9 crystal. The observed spectrum was typical for doping ions in tetravalent Mn4+ state (3d 3, S=3/2) and for main orientations of static magnetic field along the crystal axes (T=296 K) consisted of hyperfine sextuplet from electronic transition Ms= +1/2 ↔ – 1/2. Transitions Ms= ±3/2 ↔±1/2 were not detected owing to strong interaction of the spin system with crystal field as compared with electron Zeeman interaction in the X frequency range of EPR registration. The angular variations of the spectrum were measured for static field B rotated in three main crystal planes. Since only central transition (Ms= +1/2 ↔ – 1/2) was detected and the splitting of the fine structure remained unknown, the spectrum was described in the approximation of effective spin Seff=1/2. The parameters of the spin Hamiltonian, including electron Zeeman and hyperfine interactions, were calculated. The magnetic multiplicity of the spectrum (km=2) evidenced that paramagnetic centers occupied the sites with monoclinic C2 point symmetry. Taking into consideration the positional symmetry as well ionic charges and radii of the guest ion and the hosts, it was concluded that paramagnetic Mn4+ centers substituted for Ge4+ within oxygen octahedral complexes in the crystal lattice of LiNaGe4O9.

Electronic Structure and Hyperfine Interactions in Cr$$_x$$NbSe$$_2$$ (x = 0.33, 0.5) by DFT Studies

The first principles calculations of the electronic structure and hyperfine interactions of Cr\(_x\)NbSe\(_2\) (x = 0.33, 0.55) chalcogenides are presented. As a result, the values of the hyperfine fields and the parameters of the quadrupole interaction were determined for different arrangements of chromium ions. Ab initio calculations are compared with data obtained by the nuclear magnetic resonance methods on the \(^{53}\)Cr and \(^{93}\)Nb nuclei. It has been shown that Cr\(^{3+}\) ions have a high degree of hybridization of \(a_{1g}\) and \(e_g\) orbitals of 3d-electrons with 4d and 5s orbitals of niobium. It has been established that two nonequivalent environments of chromium ions coexist in Cr\(_{0.33}\)NbSe\(_2\) compound.

Dynamic spin polarization in organic semiconductors with intermolecular exchange interaction

It is shown that in organic semiconductors where organic magnetoresistance (OMAR) is observed, the exchange interaction between electrons and holes localized at different molecules leads to dynamic spin polarization in the direction of the applied magnetic field. The polarization appears even at room temperature due to the non-equilibrium conditions. The strong spin polarization requires exchange energy to be comparable with Zeeman energy in the external field and be larger or comparable with the energy of hyperfine interaction of electron and nuclear spins. The exchange interaction also modifies the lineshape of OMAR.

Study of Electron-Nuclear Interactions in Doped Calcium Phosphates by Various Pulsed EPR Spectroscopy Techniques.

Substituted calcium phosphates (CaPs) are vital materials for the treatment of bone diseases and repairing and replacement of defects in human hard tissues. In this paper, we present some applications of the rarely used pulsed electron paramagnetic resonance (EPR) and hyperfine interaction spectroscopy approaches [namely, electron spin-echo envelope modulation (ESEEM) and electron–electron double-resonance detected nuclear magnetic resonance (EDNMR)] to investigate synthetic CaPs (hydroxyapatite, tricalcium, and octacalcium phosphate) doped with various cations (Li+, Na+, Mn2+, Cu2+, Fe3+, and Ba2+). These resonance techniques provide reliable tools to obtain unique information about the presence and localization of impurity centers and values of hyperfine and quadrupole tensors. We show that revealed in CaPs by EPR techniques, radiation-induced stable nitrogen-containing species and carbonate radicals can serve as sensitive paramagnetic probes to follow CaPs’ structural changes caused by cation doping. The most pulsed EPR, ESEEM, and EDNMR spectra can be detected at room temperature, reducing the costs of the measurements and facilitating the usage of pulsed EPR techniques for CaP characterization.

EPR Spectroscopy of $$^{53}\hbox {Cr}^{3+}$$ Monoisotopic Impurity Ions in a Single Crystal of Scandium Orthosilicate $$\hbox {Sc}_{2}\hbox {SiO}_{5}$$

Monoisotopic $$^{53}\hbox {Cr}^{3+}$$ impurity ions in scandium orthosilicate single crystal ( $$\hbox {Sc}_2\hbox {SiO}_5$$ ) are studied by the method of electron paramagnetic resonance in the X-band frequencies. The directions of the main principal magnetic axes and the parameters of the effective spin Hamiltonian that describe the magnetic characteristics of the impurity centers of chromium, which replaces scandium in two structurally nonequivalent positions, are determined. It is shown that the orientation dependencies of the EPR spectra are well described by the second-order spin Hamiltonian corresponding to the orthorhombic symmetry of the local crystal field acting on the impurity ion. It was assumed that the g-tensor and the A-tensor determining the Zeeman energy of electronic levels in a magnetic field and the hyperfine interaction of electron and nuclear spins are isotropic, and the entire anisotropy of the EPR spectra is due to the anisotropy of the D-tensor, which describes the fine structure of electronic levels in a crystalline electric field. A strong dependence of the probability of “forbidden” transitions between hyperfine sublevels of electronic levels on the orientation of an external magnetic field is established. Moreover, for some orientations, the probability of “forbidden” transitions exceeds the probability of “allowed” transitions.

Drug delivery via super-paramagnetic (N2)n[SiO2(OH)2]8 Core-Shell catalyst

The MNPs @ [SiO2(OH)2]8 catalyzers were stablished via ab-initio and quantum mechanics & Molecular mechanic (QM/MM) simulation. The studies focus on how to improve the dispersion of composite particle for achieving high magnetic performances. The results revealed that the Fe3O4 @[SiO2 (OH)2]8(N2)8 as a cabalist exhibited better thermodynamic stability and dispersion than the magnetite nanoparticles. Furthermore, the particle size and magnetic properties of the [SiO2 (OH)2]8(N2)8 composite nanoparticles can be controlled by changing the functional groups. The electrical properties such as NMR Shielding, electron densities, energy densities, potential energy densities, ELF, LOL, of electron density, eta index, ECP, ESR and hyperfine interactions for Fe3O4@ [SiO2(OH)2]8(N2)8 have been calculated. As the catalyst could be easily recovered by magnetic separation and recycled for a few times without significant loss of its catalytic activity, we have calculated to obtain the stronger non bonded interaction in the Fe3O4@ [SiO2(OH)2]8(N2)8 system. This system can be used for antibiotics drug delivery instead of injection. The chemical shielding and several factors as the same electronegativity, magnetic anisotropy of π-systems will be changed due to the number of electrons The chemical shielding is a vector orientation function for all of the shielding parameters that can change in several places inside the shielding region.

EPR spectroscopy of 53Cr monoisotopic impurity ions in a single crystal of yttrium orthosilicate Y2SiO5

The electron paramagnetic resonance spectra of 53Cr monoisotopic impurity ions in yttrium orthosilicate single crystals (Y2SiO5) were studied by electron paramagnetic resonance (EPR) in the X-band. The directions of the principal magnetic axes and the parameters of the effective spin Hamiltonian, which describes magnetic characteristics of the impurity centers of chromium are determined. It is shown that the orientation dependencies of the EPR spectra are described by the second-order spin Hamiltonian corresponding to the rhombic symmetry of the local crystal field acting on the impurity ion. It was assumed that the g-tensor and A-tensor describing the Zeeman energy of electron levels in a magnetic field and the hyperfine interaction of electron and nuclear spins are isotropic, and the entire anisotropy of the EPR spectra is due to the anisotropy of the D-tensor, which describes the fine structure of electron levels in crystal electric field. A strong dependence of the probability of forbidden transitions between hyperfine sublevels of electron levels on the orientation of an external magnetic field is established. Moreover, for some orientations, the probability of forbidden transitions becomes comparable to the probability of allowed transitions.

Structural, Electronic, and Magnetic Properties and Hyperfine Interactions at the Fe Sites of the Spinel TiFe2O4. Ab Initio, XANES, and Mössbauer Study

Fil: Mudarra Navarro, Azucena Marisol. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Fisica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Fisica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Fisica La Plata; Argentina

Electron spin dynamics in mesoscopic GaN nanowires

The electron spin dynamics in spontaneously formed GaN nanowires (NWs) on Si(111) is investigated by time-resolved magneto-optical Kerr-rotation spectroscopy for temperatures from 15 to 260 K. A strong increase in the electron spin relaxation time by more than an order of magnitude is found as compared to bulk GaN. The temperature dependence of spin relaxation is characterized by two regimes, which are explained by a model taking into account the coexistence of two different mechanisms. As a result, the spin lifetime is limited by hyperfine interaction of localized electron spins with nuclear spins at low temperatures. The mesoscopic electron confinement in the NWs leads to a dominance of Dyakonov-Perel spin relaxation driven by interface-induced contributions at high temperatures, resulting in a slow-down, but not complete suppression of spin relaxation as compared to bulk GaN. These findings underline the important role of the high surface-to-volume ratio in NWs.

Electronic structure, magnetism, and hyperfine interactions in the EuRhO3 orthorhodite

The results of ab−initio electronic structure calculations, X-ray diffraction, magnetic, and 151Eu Mössbauer spectroscopy investigations of the EuRhO3 orthorhodite are presented. The orthorhodite is shown to crystallize in the orthorhombic space group Pnma and its lattice constants are a = 5.7499(1) Å, b = 7.6863(1) Å, and c = 5.3095(1) Å. The electron charge density distributions point toward the presence of a mixture of ionic and directional covalent bonding. A detailed analysis of the density of states and the energy band structure reveals half-metallic/half-insulator characteristics of EuRhO3. The Eu atoms in EuRhO3 are shown to be in the trivalent oxidation state. It is demonstrated that EuRhO3 is a paramagnet down to 2.3 K. The Debye temperature of EuRhO3 is found to be 254(3) K.

Nanoscale zero-field electron spin resonance spectroscopy

Electron spin resonance (ESR) spectroscopy has broad applications in physics, chemistry, and biology. As a complementary tool, zero-field ESR (ZF-ESR) spectroscopy has been proposed for decades and shown its own benefits for investigating the electron fine and hyperfine interaction. However, the ZF-ESR method has been rarely used due to the low sensitivity and the requirement of much larger samples than conventional ESR. In this work, we present a method for deploying ZF-ESR spectroscopy at the nanoscale by using a highly sensitive quantum sensor, the nitrogen vacancy center in diamond. We also measure the nanoscale ZF-ESR spectrum of a few P1 centers in diamond, and show that the hyperfine coupling constant can be directly extracted from the spectrum. This method opens the door to practical applications of ZF-ESR spectroscopy, such as investigation of the structure and polarity information in spin-modified organic and biological systems.

Effect of Charge Localization on the Effective Hyperfine Interaction in Organic Semiconducting Polymers.

Hyperfine interaction (HFI), originating from the coupling between spins of charge carriers and nuclei, has been demonstrated to strongly influence the spin dynamics of localized charges in organic semiconductors. Nevertheless, the role of charge localization on the HFI strength in organic thin films has not yet been experimentally investigated. In this study, the statistical relation hypothesis that the effective HFI of holes in regioregular poly(3-hexylthiophene) (P3HT) is proportional to 1/N^{0.5} has been examined, where N is the number of the random nuclear spins within the envelope of the hole wave function. First, by studying magnetoconductance in hole-only devices made by isotope-labeled P3HT we verify that HFI is indeed the dominant spin interaction in P3HT. Second, assuming that holes delocalize fully over the P3HT polycrystalline domain, the strength of HFI is experimentally demonstrated to be proportional to 1/N^{0.52} in excellent agreement with the statistical relation. Third, the HFI of electrons in P3HT is about 3 times stronger than that of holes due to the stronger localization of the electrons. Finally, the effective HFI in organic light emitting diodes is found to be a superposition of effective electron and hole HFI. Such a statistical relation may be generally applied to other semiconducting polymers. This Letter may provide great benefits for organic optoelectronics, chemical reaction kinetics, and magnetoreception in biology.

Enzymatic mechanisms of biological magnetic sensitivity.

Primary biological magnetoreceptors in living organisms is one of the main research problems in magnetobiology. Intracellular enzymatic reactions accompanied by electron transfer have been shown to be receptors of magnetic fields, and spin-dependent ion-radical processes can be a universal mechanism of biological magnetosensitivity. Magnetic interactions in intermediate ion-radical pairs, such as Zeeman and hyperfine (HFI) interactions, in accordance with proposed strict quantum mechanical theory, can determine magnetic-field dependencies of reactions that produce biologically important molecules needed for cell growth. Hyperfine interactions of electrons with nuclear magnetic moments of magnetic isotopes can explain the most important part of biomagnetic sensitivities in a weak magnetic field comparable to the Earth's magnetic field. The theoretical results mean that magnetic-field dependencies of enzymatic reaction rates in a weak magnetic field that can be independent of HFI constant a, if H << a, and are determined by the rate constant of chemical transformations in the enzyme active site. Both Zeeman and HFI interactions predict strong magnetic-field dependence in weak magnetic fields and magnetic-field independence of enzymatic reaction rate constants in strong magnetic fields. The theoretical results can explain the magnetic sensitivity of E. coli cell and demonstrate that intracellular enzymatic reactions are primary magnetoreceptors in living organisms. Bioelectromagnetics. 38:511-521, 2017. © 2017 Wiley Periodicals, Inc.

A study of magnetic and electronic hyperfine interactions in epitaxial film of yttrium-iron garnet by the method of conversion electron Mössbauer spectroscopy

Magnetic and electric hyperfine interactions in the near-surface layers of epitaxial films of yttrium-iron garnet of the (111) orientation grown by the liquid-phase epitaxy method are studied by the method of the conversion electron Mossbauer spectroscopy (CEMS). The studies reveal a stoichiometric violation of the anion sublattice in the near-surface layers (≈8 × 10–8 m) of yttrium iron garnet film and, as a consequence, the formation of two types of d-sites, which is associated with a significant concentration of point defects in the anion sublattice of the near-surface area and the growing weight of the covalent bonding in the transition film–air layer. This also causes the presence of a fixed doublet component corresponding to iron ions in a paramagnetic state with an intermediate degree of valency between +2 and +3. It is shown that interpretation of the spectroscopic results using the Hamiltonian of mixed magnetic and quadrupole interactions makes it possible to obtain a vector diagram of the spatial orientations of the effective magnetic fields at the Fe57 nuclei and, as a consequence, to reconstruct the formation mechanism of the resulting vector of the magnetic moment of the yttrium iron garnet epitaxial film. Our studies reveal a slight noncollinearity of ≈4° in the orientations of the magnetic moments in the a- and d-sites of iron. The obtained results complement the picture of the magnetic and electronic hyperfine interactions in the epitaxial ferrite-garnet films and should be considered in the practical applications of the magnetic properties of such materials.

Theory of Ultralong-Range Rydberg Molecule Formation Incorporating Spin-Dependent Relativistic Effects: Cs(6s)-Cs(np) as Case Study.

We calculate vibrational spectra of ultralong-range Cs(32p) Rydberg molecules that form in an ultracold gas of Cs atoms. We account for the partial-wave scattering of the Rydberg electrons from the Cs perturber atoms by including the full set of spin-resolved 1,3 SJ and 1,3 PJ scattering phase shifts, and allow for the mixing of singlet (S=0) and triplet (S=1) spin states through Rydberg electron spin-orbit and ground state electron hyperfine interactions. Excellent agreement with observed data in Saßmannshausen et al. [Phys. Rev. Lett. 2015, 113, 133201] in line positions and profiles is obtained. We also determine the spin-dependent permanent electric dipole moments for these molecules. This is the first such calculation of ultralong-range Rydberg molecules for which all of the relativistic contributions are accounted.

Spin dynamics of hopping electrons in quantum wires: Algebraic decay and noise

We study theoretically spin decoherence and intrinsic spin noise in semiconductor quantum wires caused by an interplay of electron hopping between the localized states and the hyperfine interaction of electron and nuclear spins. At a sufficiently low density of localization sites the hopping rates have an exponentially broad distribution. It allows the description of the spin dynamics in terms of closely-situated "pairs" of sites and single "reaching" states, from which the series of hops result in the electron localized inside a "pair". The developed analytical model and numerical simulations demonstrate disorder-dependent algebraic tails in the spin decay and power-law singularity-like features in the low-frequency part of the spin noise spectrum.

Spin noise of electrons and holes in (In,Ga)As quantum dots: Experiment and theory

The spin fluctuations of electron and hole doped self-assembled quantum dot ensembles are measured optically in the low-intensity limit of a probe laser in absence and presence of longitudinal or transverse static magnetic fields. The experimental results are modeled by two complementary approaches based either on semiclassical or quantum mechanical descriptions. This allows us to characterize the hyperfine interaction of electron and hole spins with the surrounding bath of nuclei on time scales covering several orders of magnitude. Our results demonstrate (i) the intrinsic precession of the electron spin fluctuations around the effective nuclear Overhauser field caused by the host lattice nuclear spins, (ii) the comparably long time scales for electron and hole spin decoherence, as well as (iii) the dramatic enhancement of the spin lifetimes induced by a longitudinal magnetic field due to the decoupling of nuclear and charge carrier spins.

Exploring template-bound dinuclear copper porphyrin nanorings by EPR spectroscopy.

Electron paramagnetic resonance (EPR) spectroscopy has been used to study the molecular geometry as well as metal-ligand interactions in ten-membered porphyrin nanorings ( c-P10Cu2 ) containing two copper and eight zinc centers. The presence of copper in the structures allows intramolecular interactions, including dipolar interactions between electron spins and hyperfine interactions to be quantified. Results obtained for c-P10Cu2 samples bound to two molecular templates with four or five binding sites, respectively, are compared to those obtained for a sample of the porphyrin ring in the absence of any templates. It is shown that the observed lower binding affinity of the nitrogen ligand to copper as compared to zinc has a strong impact on the geometries of the respective template-bound c-P10Cu2 structures. The interaction between the central copper atom and nitrogen ligands is weak, but pulsed EPR hyperfine techniques such as ENDOR and HYSCORE are very sensitive to this interaction. Upon binding of a nitrogen ligand to copper, the hyperfine couplings of the in-plane nitrogen atoms of the porphyrin core are reduced by about 3 MHz. In addition, the copper hyperfine couplings as well as the g-factors are altered, as detected by continuous wave EPR. DFT calculations of the hyperfine coupling tensors support the assignment of the measured couplings to the nuclei within the structure and reproduce the experimentally observed trends. Finally, Double Electron Electron Resonance (DEER) is used to measure the distances between the copper centers in a range between 2.5 and 5 nm, revealing the preferred geometries of the template-bound nanorings.

Quantum transport in carbon nanotubes

Carbon nanotubes are a versatile material in which many aspects of condensed matter physics come together. Recent discoveries, enabled by sophisticated fabrication, have uncovered new phenomena that completely change our understanding of transport in these devices, especially the role of the spin and valley degrees of freedom. This review describes the modern understanding of transport through nanotube devices. Unlike conventional semiconductors, electrons in nanotubes have two angular momentum quantum numbers, arising from spin and from valley freedom. We focus on the interplay between the two. In single quantum dots defined in short lengths of nanotube, the energy levels associated with each degree of freedom, and the spin-orbit coupling between them, are revealed by Coulomb blockade spectroscopy. In double quantum dots, the combination of quantum numbers modifies the selection rules of Pauli blockade. This can be exploited to read out spin and valley qubits, and to measure the decay of these states through coupling to nuclear spins and phonons. A second unique property of carbon nanotubes is that the combination of valley freedom and electron-electron interactions in one dimension strongly modifies their transport behaviour. Interaction between electrons inside and outside a quantum dot is manifested in SU(4) Kondo behavior and level renormalization. Interaction within a dot leads to Wigner molecules and more complex correlated states. This review takes an experimental perspective informed by recent advances in theory. As well as the well-understood overall picture, we also state clearly open questions for the field. These advances position nanotubes as a leading system for the study of spin and valley physics in one dimension where electronic disorder and hyperfine interaction can both be reduced to a very low level.