Super Hyperfine Research Articles

Effect of the Landau Levels on the Super Hyperfine Structure of ESR Spectra of Fe3+ Precipitates in Dirac 3D Semimetal Cd3As2

The influence of d-metal impurities on the magnetic and transport properties of 3D topological semimetal Cd3As2 has been experimentally studied. It is found that alloying with iron does not change the sign of magnetoresistance (in contrast to Eu). Amplification of oscillations of the parameters (magnetic susceptibility, contact potential difference, and conductivity) related to oscillations of the density of states at the Fermi level is observed with a change in temperature and magnetic field. ESR signals from Fe2+ ions (which are most likely the main type of Fe impurity in Cd3As2) have not been detected in the temperature range of 10–300 K. Weak ESR signals with a super hyperfine structure, which is obviously affected by the Landau levels, have been observed from Fe3+ ions.

Role of indium in controlling the magnetic properties of bulk and nano magnetic systems

ABSTRACTIn the present ferrites (soft & hard) series, Saturation Magnetization, increases only at lowers concentration of Indium. The cation distribution from Mössbauer analysis indicates that Indium ion at lower concentration (10 to 20%) goes to tetrahedral site only, whereas higher concentration it goes octahedral sites also. Magnetization has been explained on the basis of super exchange hyperfine interactions as well as cation distribution of magnetic ions as per the Neel's two sub lattice model of ferromagnetism. In all the chosen ferrite series magnetic behavior is consistent with substitution of dopant (In3+ ions). Ferromagnetic results are further authenticated by Mössbauer Spectroscopic analysis.

Detailed Analysis of Manifestations of the Spin Coherence Transfer in EPR Spectra of 14N Nitroxide Free Radicals in Non-Viscous Liquids

Manifestations of the spin coherence transfer induced by the exchange and dipole–dipole interactions between spin probes in dilute solutions in the electron paramagnetic resonance (EPR) spectra have been studied. The perturbation theory of manifestations of the spin coherence transfer in the EPR spectra of nitroxide free radicals elaborated by one of the authors Salikhov (Applied Magnetic Resonance 38:237–256, 2010) has been generalized with allowance for the super hyperfine structure of the EPR spectra. For 14N nitroxide radicals, the total EPR spectrum was presented as a sum of three independent components in the case of slow and intermediate spin coherence transfer rates. The shapes of these components were found. The side components of the EPR spectrum contain the absorption and dispersion contributions and, as a result, have the asymmetric (mixed) shapes. These asymmetric components can be presented as J = Jabsorption ± pJdispersion. The p value is found for the arbitrary super hyperfine structure of the spectrum. In the slow and intermediate spin coherence transfer rate regime, the parameter p is independent of the super hyperfine interactions in the nitroxide radicals, but the shapes of Jabsorption and Jdispersion terms depend on the super hyperfine structure of the nitrogen components of the nitroxide EPR spectrum and on the spin coherence transfer rate. It is confirmed theoretically that a good strategy to evaluate the spin coherence transfer rate from the EPR spectra is using the dispersion contribution to the shape of the EPR spectra of nitroxide free radicals. An algorithm is suggested and tested for determining the spin coherence transfer and spin decoherence rates.

The interaction of H2O2 with TiAlPO-5 molecular sieves: probing the catalytic potential of framework substituted Ti ions

A combination of EPR, ENDOR and HYSCORE experiments has been used to investigate the reactivity of hydrogen peroxide with TiAlPO-5 materials under both hydrated and anhydrous conditions. Superoxide radical anions, generated upon reaction, are used as paramagnetic probes to investigate the nature and reactivity of framework incorporated Ti ions. Super hyperfine interactions with (27)Al, (31)P and (1)H are resolved, which allow a detailed mapping of the local environment of the adsorbed O2(-) ions. Evidence is provided for the first time of a specific redox activity associated with Ti ions incorporated at framework Al sites of TiAlPO materials.

Structural and Spectroscopic Features of Mixed Valent FeIIFeI Complexes and Factors Related to the Rotated Configuration of Diiron Hydrogenase

The compounds of this study have yielded to complementary structural, spectroscopic (Mössbauer, EPR/ENDOR, IR), and computational probes that illustrate the fine control of electronic and steric features that are involved in the two structural forms of (μ-SRS)[Fe(CO)2PMe3]2(0,+) complexes. The installation of bridgehead bulk in the -SCH2CR2CH2S- dithiolate (R = Me, Et) model complexes produces 6-membered FeS2C3 cyclohexane-type rings that produce substantial distortions in Fe(I)Fe(I) precursors. Both the innocent (Fc(+)) and the noninnocent or incipient (NO(+)/CO exchange) oxidations result in complexes with inequivalent iron centers in contrast to the Fe(I)Fe(I) derivatives. In the Fe(II)Fe(I) complexes of S = 1/2, there is complete inversion of one square pyramid relative to the other with strong super hyperfine coupling to one PMe3 and weak SHFC to the other. Remarkably, diamagnetic complexes deriving from isoelectronic replacement of CO by NO(+), {(μ-SRS)[Fe(CO)2PMe3] [Fe(CO)(NO)PMe3](+)}, are also rotated and exist in only one isomeric form with the -SCH2CR2CH2S- dithiolates, in contrast to R = H ( Olsen , M. T. ; Bruschi , M. ; De Gioia , L. ; Rauchfuss , T. B. ; Wilson , S. R. J. Am. Chem. Soc. 2008 , 130 , 12021 -12030 ). The results and redox levels determined from the extensive spectroscopic analyses have been corroborated by gas-phase DFT calculations, with the primary spin density either localized on the rotated iron in the case of the S = 1/2 compound, or delocalized over the {Fe(NO)} unit in the S = 0 complex. In the latter case, the nitrosyl has effectively shifted electron density from the Fe(I)Fe(I) bond, repositioning it onto the spin coupled Fe-N-O unit such that steric repulsion is sufficient to induce the rotated structure in the Fe(II)-{Fe(I)((•)NO)}(8) derivatives.

Relation between susceptibility and Knight shift inLa2NiO4.17andK2NiF4byN61iNMR

The ${\text{NiO}}_{4}$ plaquettes in ${\text{La}}_{2}{\text{NiO}}_{4.17}$, a cousin of the hole-doped high-temperature superconductor ${\text{La}}_{2\ensuremath{-}x}{\text{Sr}}_{x}{\text{CuO}}_{4}$, have been studied by $^{61}\text{N}\text{i}$ NMR in 14 T in a single crystal enriched in $^{61}\text{N}\text{i}$. Doped and undoped plaquettes are discriminated by the shift of the NMR resonance, leading to a small line splitting, which hardly depends on temperature or susceptibility. The smallness of the effect is additional evidence for the location of the holes as deduced by Sch\"u\ss{}ler-Langenheine et al. [Phys. Rev. Lett. 95, 156402 (2005)]. The increase in linewidth with decreasing temperature shows a local-field redistribution, consistent with the formation of charge-density waves or stripes. For comparison, we studied, in particular, the grandmother of all planar antiferromagnets ${\text{K}}_{2}{\text{NiF}}_{4}$ in the paramagnetic state using natural abundant $^{61}\text{N}\text{i}$. The hyperfine fields in both two-dimensional compounds appear to be remarkably small, which is well explained by super(transferred) hyperfine interaction. In ${\text{K}}_{2}{\text{NiF}}_{4}$, the temperature dependence of the susceptibility and the Knight shift cannot be brought onto a simple scaling curve. This unique feature is ascribed to a different sensitivity for correlations of these two parameters.

Spin‐coupling and hyperfine interaction of the nitrogen donors in 6H‐SiC

AbstractThe X‐, Q‐band field‐sweep electron spin echo (FS ESE) study of n‐type 6H‐SiC wafers shows besides the well known hyperfine (hf) triplet lines of14N on two quasi‐cubic (Nc1, Nc2) and hexagonal (Nh) sites additional triplet lines (Nx) of comparatively low intensity with ag‐tensor of about the average value of the Nc2and Nhspectrum at 4.2 K. The Nxtriplet has half of the hf splitting with respect to the nitrogen residing at cubic sites Nc2. Pulsed electron nuclear double resonance (ENDOR) measurements performed on the NxEPR triplet line demonstrate that there is an efficient spin‐coupling between Nhand Nxnitrogen related centers. The Nxtriplet lines were attributed to distant donor Nc–Nhpairs between nitrogen atoms residing at quasi‐cubic and hexagonal sites having a total electron spinS= 1, which were found before in n‐type 4H‐SiC. Based on Q‐band FS ESE and X‐band pulsed ENDOR measurements the values of the hf interaction for Nc1, Nc2were reassigned with respect to the assignment accepted hitherto.The super hyperfine (shf) interaction with neighboring atoms of nitrogen on the quasi‐cubic lattice sites was studied by FS ESE and pulsed ENDOR. The new shf lines due to29Si and13C atoms with large shf interaction which were not observed previously were found in nitrogen FS ESE and ENDOR spectra. One of them, with the largest shf splitting (23.12 MHz), were attributed to the29Si atoms along thec‐axis in nearest‐neighbor positions of nitrogen on the quasi‐cubic sites which unambiguously confirms that nitrogen substitute carbon lattice site in 6H‐SiC. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron spin relaxation andK39pulsed ENDOR studies onCr5+-dopedK3NbO8at 9.7 and 240 GHz

${\text{Cr}}^{5+}$-doped ${\text{K}}_{3}{\text{NbO}}_{8}$, considered to be useful as an electron spin qubit, has been investigated by pulsed $X$ band $(\ensuremath{\sim}9.7\text{ }\text{GHz})$ and 240 GHz electron paramagnetic resonance and electron nuclear double resonance (ENDOR). Comparison of the low temperature electronic spin-lattice relaxation rate $1/{T}_{1}$ at 9.7 and 240 GHz shows that it is 250 times faster at 240 GHz than at $X$ band. On the other hand, spin-spin relaxation rate $1/{T}_{2}$ appears largely frequency independent and is very likely related to the superhyperfine (SHF) coupling of the ${\text{Cr}}^{5+}$ electron with the surrounding potassium and niobium nuclei. This coupling was investigated by hyperfine sublevel correlation spectroscopy at 9.7 GHz and pulsed Mims ENDOR at 240 GHz. The use of high frequency and field enabled us to unambiguously measure the hyperfine and quadrupole couplings of the $^{39}\text{K}$ in spite of its small magnetic moment. We find that the largest $^{39}\text{K}$ SHF coupling is positive, with 0.522 and 0.20 MHz as its isotropic and dipolar parts, respectively. $^{93}\text{N}\text{b}$ ENDOR was dominantly due to its quadrupolar interaction with a coupling of about 0.8 MHz and a SHF coupling of about 0.08 MHz. The significance of these data to spin qubit studies is pointed out.

EPR and ENDOR analysis of Fe3+ impurity centers in fluoroelpasolite lattices

Fe(3+) ions in hexagonal and cubic fluoroelpasolite crystals (A(1)(2)B(I)M(III)F(6)) have been investigated in a combined Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) study. A detailed analysis of the ENDOR spectra for the nearest (19)F and (23)Na shells in X (9.5 GHz) and Q band (34 GHz) allowed the complex EPR spectra to be disentangled and to determine the spin Hamiltonian parameters for the various S = 5/2 Fe(3+) centres. W-band (95 GHz) EPR measurements as a function of temperature were performed to provide unambiguous evidence about the absolute signs of the Zero Field Splitting (ZFS) and SuperHyperFine (SHF) parameters for Fe(3+) in Cs(2)NaAlF(6) as already determined from the ENDOR work. It could be concluded that all principal (19)F hyperfine values were positive, in agreement with earlier assignments in the literature for related systems. A comparative analysis of the (19)F SHF data for Fe(3+) at a perfectly octahedral site in the cubic crystal, and at two slightly trigonally distorted environments in the hexagonal crystals, indicates that the metal-to-ligand distance changes upon doping. The obtained set of parameters concerning one defect in various analogous environments can furthermore be used to test different methods of theoretical calculations for ZFS and SHF values.

Electron paramagnetic resonance study of 3,4,5-trimethoxytetraphenyl porphyrinoxovanadium (IV) complex

3,4,5-Trimetoxytetraphenylporphyrinoxovanadium (IV) complex (3,4,5-TMVOTPP) was synthesized by a new one pot synthetic method. The complex was studied in the form of single crystal, powder (polycrystalline state), solution and frozen solution (glassy state) by electron paramagnetic resonance (EPR) between room temperature (RT) and liquid nitrogen temperature (LNT). Interestingly a well-resolved octet in the EPR spectrum at RT is observed in the pure paramagnetic state of the crystal. This observation is attributed to a greatly reduced dipolar interaction between paramagnetic vanadyl ions due to the large size of the molecule and the resultant stacking in the crystalline state. The line width of the EPR signals in single crystal at RT is ∼3.3 mT 1 1 1 mT = 10 G. which is more than the usual line width in diluted paramagnets (∼1.5 mT) and is attributed to some kind of broadening effect akin to slow motion broadening. The line width in solvents is more than the crystal value but decreases appreciably at low temperatures. The decrease in line width at low temperature is attributed to the increase in spin-lattice-relaxation time and quenching of RT broadening motion. Only one octet is observed in the crystal EPR spectra which suggests only one formula unit per unit cell or a parallel/antiparallel ordering of V O vectors in case the formula units per unit cell are more than one. This result needs verification by a detailed X-ray investigation. The crystalline field symmetry around the V 4+ metal ion is revealed to be axial by the observed angular dependence of the EPR spectrum and the powder EPR spectrum. No super hyperfine splitting of the hyperfine lines of the vanadyl ion is observed in solid state or diluted glass up to liquid nitrogen temperature. This suggests an expected weak in-plane π-bonding with ligands. The spin Hamiltonian parameters for vanadyl ion in crystal, powder, diluted solutions and frozen glasses are evaluated and discussed.

Interface Defects in n-Type 3C-SiC/SiO<sub>2</sub>: An EPR Study of Oxidized Porous Silicon Carbide Single Crystals

The defects at the 3C-SiC/SiO2 interface have been studied by X-band EPR spectroscopy in oxidized porous 3C-SiC. One interface defect is detected; its spin Hamiltonian parameters, spin S=1/2, C3V symmetry, g//=2.00238 and g⊥=2.00317, central hyperfine interaction (CHF) with one carbon atom and AB//[001]=48G and superhyperfine (SHF) interaction with three equivalent Si neighbour atoms and TB//[001]=12.4G, allow us to attribute the center to a sp3 coordinated carbon dangling bond center, PbC.

Comparing continuous wave progressive saturation EPR and time domain saturation recovery EPR over the entire motional range of nitroxide spin labels

The measurement of spin–lattice relaxation rates from spin labels, such as nitroxides, in the presence and absence of spin relaxants provides information that is useful for determining biomolecular properties such as nucleic acid dynamics and the interaction of proteins with membranes. We compare X-band continuous wave (CW) and pulsed or time domain (TD) EPR methods for obtaining spin–lattice relaxation rates of spin labels across the entire range of rotational motion to which relaxation rates are sensitive. Model nitroxides and spin-labeled biological species are used to illustrate the potential complications that arise in extracting relaxation data under conditions typical to biological experiments. The effect of super hyperfine (SHF) structure is investigated for both CW and TD spectra. First and second harmonic absorption and dispersion CW spectra of the nitroxide spin label, TEMPOL, are all fit simultaneously to a model of SHF structure over a range of microwave amplitudes. The CW spectra are novel because all harmonics and microwave phases were acquired simultaneously using our homebuilt CW/TD spectrometer. The effect of the SHF structure on the pulsed free induction decay (FID) and pulsed saturation recovery spectrum is shown for both protonated and deuterated TEMPOL. We present novel pulsed saturation recovery measurements on biological molecules, including spin–lattice relaxation rates of spin-labeled proteins and spin-labeled double-stranded DNA. The impact of structure and dynamics on relaxation rates are discussed in the context of each of these examples. Collisional relaxation rates with oxygen and transition metal paramagnetic relaxants are extracted using both continuous wave and time domain methods. The extent of the errors inherent in the CW method and the advantages of pulsed methods for unambiguously measuring collisional relaxation rates are discussed. Spin–lattice relaxation rates, determined by both CW and pulsed methods, are used to determine the electrostatic potential on the surface of a protein.

Spectroscopic investigation of hard and soft metal binding sites in synthetic melanin

Understanding the interaction of metal ions with melanin structures is essential to know some intricate functions of this kind of compounds in the living systems. The coordination chemistry of vanadyl oxycation, VO(II), and copper, Cu(II), in a synthetic l-dopa melanin (SM) was investigated using electron paramagnetic resonance (EPR), Fourier transform infrared (FT IR) and ultraviolet–visible (UV–Vis) spectroscopy. The EPR and FT IR spectra indicated axially coordinated VO(II) ions bound to catecholate functional groups, and a fraction of the Cu(II) ions in a square planar structure partially coordinated to carboxylate functional groups. The resolved EPR perpendicular super hyperfine splitting constant, A N⊥, and the Cu(II) complex EPR parallel parameters g ‖ and A ‖ values indicated two magnetically equivalent nitrogen atoms in a plane with the coordination sphere, CuN 2O 2. The ultraviolet–visible (UV–Vis) spectra of solid samples indicate supramolecular structure constitution for the synthesized VO(II)SM and Cu(II)SM complexes.

Al- and OH-related paramagnetic impurity centres in UV- or x-irradiatedZnWO4 single crystals

Using electron paramagnetic resonance (EPR) and in one case also electron nucleardouble resonance new trapped electron and hole centres are characterised inZnWO4 single crystals. Inundoped and Al-doped ZnWO4 a new W5+-typedefect is produced by UV- or x-irradiation at 77 K. The centre is stabilised by a nearbyAl3+ impurity that issubstituting for Zn2+.In ZnWO4:Al in addition to the above electron-type defect three kinds of hole-type centrescreated by x-irradiation at 77 K are also studied: one of these is assigned to anO− ion near aVZn–AlZn3+ complex, andthe second to an O− ion near a VZn–OH− pair. The - and hydrogen super hyperfine (SHF) tensors of the latter centre have been publishedpreviously. Due to the higher concentration in the Al-doped crystal, SHF tensors of two Wneighbours could also be determined. The third hole-type defect shows quartet SHF(I = 3/2) with a 100% abundant nucleus and therefore theO− in this centre is mostlikely stabilised by an Na+ impurity. Complete sets of EPR parameters are compared for trapped electron and trappedhole centres including previously characterised defects.

First observation of the hyperfine and superhyperfine structure of antiprotonic helium by laser-microwave spectroscopy

We have designed and developed a laser-microwave triple resonance spectroscopy experiment of antiprotonic helium to investigate its hyperfine (HF) and superhyperfine (SHF) structures. We succeeded in making microwave transitions between HF substates of the ( n, l) = (37, 35) metastable state, and resolved doublet resonance peaks split by SHFS. We determined the resonance frequencies with 30ppm precision. The experimental values agree with recent theoretical calculations, and to ∼ 60ppm level three-body QED theory is verified.

Electron-phonon coupling inNi2+−dopedperovskites:KMgF3andBaLiF3

Electron-phonon (e-ph) coupling has been studied in two ${\mathrm{Ni}}^{2+}\ensuremath{-}\mathrm{d}\mathrm{o}\mathrm{p}\mathrm{e}\mathrm{d}$ fluoride crystals: the classical ${\mathrm{KMgF}}_{3}$ perovskite and the inverted perovskite ${\mathrm{BaLiF}}_{3}.$ The purely linear character of the EP coupling is shown through the comparison of emission or excitation vibronic spectra arising from different electronic levels at low temperature and the thermal evolution of the spectra. The $[{\mathrm{NiF}}_{6}{]}^{4\ensuremath{-}}\mathrm{complex}$ is described by using the molecular orbital formalism, and its covalency is estimated from the parameters of the super hyperfine structure observed in electron spin resonance measurements. A modified Pryce model is used to simulate the vibronic band shapes of ${\mathrm{Ni}}^{2+}$ ions in the compounds from their measured phonon density of states and to estimate the Huang-Rhys S parameter. The strength of the crystal field and the strength of the e-ph coupling experienced by the ${\mathrm{Ni}}^{2+}$ ions is shown to increase with the covalency of the bonding. No effect on e-ph coupling has been observed when the concentration of doping ions has been increased.

Unusual line widths in the EPR spectra of copper(II) dithizonate

Unusually wide lines have been found in the EPR spectra of copper(II) complex with dithizone (H2Dz), in which the super hyperfine structure (SHFS) from ligand atoms was not resolved.

EPR studies of Cu2+ in K1−xLixTaO3

Electron paramagnetic resonance (EPR) of copper centers in KTaO3:Li:Cu single crystals have been studied. Superhyperfine (SHF) structure of an exchange pair Cu2+-Cu2+ center, associated with the eight surrounding nearest-neighbor potassium ions was found. The EPR signal behaviour with the temperature may characterize the dielectric properties of crystals at the microwave frequency.

Site of Interaction of Copper on Bacillus Polymyxa

Copper uptake potential of different bacterial strains isolatedfrom contaminated soil was compared. The bacterial strainidentified as Bacillus polymyxa showed maximum copperuptake capacity. An attempt was made to elucidate the site ofinteraction of Cu(II) with B. polymyxa using electronparamagnetic resonance (EPR) studies. The EPR spectra showedthat accumulated copper formed complexes with oxygen andnitrogen which may be the carboxyl groups of cell-wallpeptidoglycan and nitrogen atoms of aminosugars or structuralproteins. The absence of super hyperfine splitting in theg ⊥ region of EPR spectra of treated B. polymyxa cellsafter Cu(II) uptake indicated that copper could be coordinatedwith the oxygen atoms from carboxyl groups of peptidoglycan inthe cell walls.

ESR study of photoinduced defects in isotopically enriched quasi-one-dimensional chlorine-bridged platinum complexes

Photoinduced defects in the quasi-one-dimensional chlorine-bridged platinum complex, [Pt{sup II}(en){sub 2}][Pt{sup IV}(en){sub 2}Cl{sub 2}](ClO{sub 4}){sub 4}, where en=ethylenediamine, C{sub 2}N{sub 2}H{sub 8}, were investigated by light-induced electron-spin resonance (LESR). Using samples prepared with enriched nuclear isotopes including {sup 194}Pt (I=0), {sup 2}H (I=1), and {sup 37}Cl (I=3/2, magnetogyric ratio {approximately}83{percent} that of {sup 35}Cl), the hyperfine and superhyperfine (SHF) patterns in the LESR spectra were fully characterized. The SHF structure (16 G average spacing) is unequivocally assigned to the bridging chlorines by comparison of the LESR spectra from samples with natural abundance Cl with samples enriched with {sup 37}Cl. The LESR spectra were analyzed at g{sub {perpendicular}}, g{sub {parallel}}, and intermediate angles by simulation of both the polaron and soliton-spin distributions. The results at temperatures above 6 K were found to be in better agreement with the neutral soliton assignment advanced by Kuroda and co-workers. The spectra from 6 to 140 K do not indicate motional narrowing as has been previously suggested. Below 6 K, surprisingly, the LESR spectra of both the natural and isotopically enriched samples exhibit an unusual dependence on temperature, modulation frequency, or microwave power, which indicates the presence of a localized dynamic process. Two other typesmore » of defect which exhibit strong sample-to-sample variability were also discovered in the LESR spectra: one is likely a spin triplet, and the other appears only at temperatures above approximately 120 K and is quite intense and stable at room temperature. {copyright} {ital 1997} {ital The American Physical Society}« less