Resonance Fine Structure Research Articles

Surface anisotropy energy in terms of magnetocrystalline anisotropy fields in ferromagnetic semiconductor (Ga,Mn)As thin films

Surface anisotropy energy density is a key quantity in the description of the dynamics of surface spins in ferromagnetic thin films and is known to result in a ferromagnetic resonance fine structure of a thin film: A multipeak spectrum is observed in an effect known as spin-wave resonance (SWR). The so-called surface pinning parameter, directly correlated with the surface anisotropy energy, plays a fundamental role in determining the character of an SWR spectrum in the theory of SWR based on the surface inhomogeneity model. Here we extend the theory of SWR by introducing a new formula representing the surface pinning parameter as a series of contributions from different anisotropies existing in (Ga,Mn)As thin films. We show how to determine the coefficients in this series by comparing the SWR theory with data obtained in a resonance experiment. The proposed procedure allows one to determine the proportion with which each type of the anisotropy contributes to the total surface anisotropy of (Ga,Mn)As, and, consequently, to assess to what extent the proportions on the surface differ from those in the bulk. The presented considerations can be used for the study of any other thin-film system, since we provide also a general rule that allows one to express the surface pinning parameter of a thin film, as well as its surface anisotropy energy, by the free energy of the considered thin-film system. This enables the interpretation of experimental SWR spectra in terms of the free-energy density of the thin film.

Detailed Impurity Phase Investigation by X-ray Absorption Fine Structure and Electron Spin Resonance Analyses in Synthesis of CaMgSi2O6:Eu Phosphor

Impurity phases of CaMgSi2O6:Eu (CMS) phosphor have been investigated in detail by X-ray absorption fine structure (XAFS), ESR, X-ray diffraction (XRD) and photoluminescence (PL) analyses. XRD studies of CMS phosphor powders clarify the volume fraction of CMS, Ca2MgSi2O7, (Ca,Eu)10(SiO4)6O2, and crystalline SiO2. XAFS and ESR studies clarify that the soluble limit of Eu ions in CMS crystals is observed at about 0.01 mol. Excess Eu ions yield an impurity (Ca,Eu)10(SiO4)6O2 and some of them are captured by another impurity Ca2MgSi2O7. From the results of XAFS, ESR, XRD, and PL measurements, it was revealed that the PL peak intensities under 147 and 360 nm excitation correlate closely with the amount of these impurity phases containing divalent and trivalent Eu ions. Variation of X-ray absorption near edge structure and ESR spectra indicate that the optimum Eu concentration of the CMS phosphor is at approximately 0.01 molar versus Ca.

35/37Cl and 16/18O isotope resolved 195Pt NMR: unique spectroscopic ‘fingerprints’ for unambiguous speciation of [PtCln(H2O)6−n]4−n (n = 2–5) complexes in an acidic aqueous solution

At high magnetic fields the 128.8 MHz (195)Pt NMR of all the species in the series [PtCl(n)(H(2)O)(6-n)](4-n) (n = 2-6) display unique (35/37)Cl isotope effects resulting in a unique 'fine-structure' of each individual resonance, which constitutes an unambiguous spectroscopic 'fingerprint' characteristic of the structure of the octahedral platinum(IV) complex, provided (195)Pt NMR are recorded at optimum magnetic field homogeneity and carefully controlled temperature (293 ± 0.1 K). The detailed (195)Pt resonance fine-structure observed experimentally can readily be accounted for by an isotopologue and isotopomer model for each complex, showing particularly noticeable differences between stereoisomer pairs such as the cis/trans- and fac/mer-complexes. Moreover partial isotopic (18)O enrichment of the coordinated water molecules in the series [Pt(35/37)Cl(n)(H(2)(16/18)O)(6-n)](n-2) (n = 2-6) confirms this model. This technique can thus be considered a novel, direct spectroscopic method of chemical speciation of appropriate platinum(IV) complexes in solution without reference to accurate chemical shifts of authentic members of such a series. These effects are interpreted qualitatively in terms of the high sensitivity of (195)Pt NMR shielding to very small and subtle Pt-(35/37)Cl and Pt-(16/18)OH(2) bond displacements. Preliminary work shows this also applied to the corresponding bromido-complexes.

Extended X-ray Absorption Fine Structure and Nuclear Resonance Vibrational Spectroscopy Reveal that NifB-co, a FeMo-co Precursor, Comprises a 6Fe Core with an Interstitial Light Atom

NifB-co, an Fe-S cluster produced by the enzyme NifB, is an intermediate on the biosynthetic pathway to the iron molybdenum cofactor (FeMo-co) of nitrogenase. We have used Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy together with (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to probe the structure of NifB-co while bound to the NifX protein from Azotobacter vinelandii. The spectra have been interpreted in part by comparison with data for the completed FeMo-co attached to the NafY carrier protein: the NafY:FeMo-co complex. EXAFS analysis of the NifX:NifB-co complex yields an average Fe-S distance of 2.26 A and average Fe-Fe distances of 2.66 and 3.74 A. Search profile analyses reveal the presence of a single Fe-X (X = C, N, or O) interaction at 2.04 A, compared to a 2.00 A Fe-X interaction found in the NafY:FeMo-co EXAFS. This suggests that the interstitial light atom (X) proposed to be present in FeMo-co has already inserted at the NifB-co stage of biosynthesis. The NRVS exhibits strong bands from Fe-S stretching modes peaking around 270, 315, 385, and 408 cm(-1). Additional intensity at approximately 185-200 cm(-1) is interpreted as a set of cluster "breathing" modes similar to those seen for the FeMo-cofactor. The strength and location of these modes also suggest that the FeMo-co interstitial light atom seen in the crystal structure is already in place in NifB-co. Both the EXAFS and NRVS data for NifX:NifB-co are best simulated using a Fe 6S 9X trigonal prism structure analogous to the 6Fe core of FeMo-co, although a 7Fe structure made by capping one trigonal 3S terminus with Fe cannot be ruled out. The results are consistent with the conclusion that the interstitial light atom is already present at an early stage in FeMo-co biosynthesis prior to the incorporation of Mo and R-homocitrate.

Ligand-field treatment for the optical and electron paramagnetic resonance spectra of ZnO:V 3+

In this work, a full ligand-field energy matrix ( 45 × 45 ) diagonalization treatment for 3d 2 ions in trigonal symmetry C 3 v is performed on the basis of a central metal ion–ligand covalency model including the ligand spin–orbit (SO) coupling. Optical fine structure and electron paramagnetic resonance (EPR) spectra of ZnO:V 3+ are uniformly explained.

Ferromagnetic Resonance Fine Structure of Dispersed Magnets: Physical Origin and Applications

An original approach is proposed to study the dipole–dipole interparticle interactions in dispersed magnets. It is the registration and analysis of the noiselike ferromagnetic resonance fine structure, which is caused by the magnetic dipole–dipole interaction between magnetic domains. The features of fine structure formation are discussed. The experimental examples of the possible applications of the fine structure method are given.

Angle-resolved photoemission spectroscopy study of [formula omitted

The Ce 4f electronic structure of a CDW system CeTe 2 has been investigated using high-resolution angle-resolved photoemission spectroscopy (ARPES). By employing the fine-structure (FS) resonance, the Ce 4f ARPES spectra have been measured. The FS resonance ARPES shows a typical two-peak structure with the peaks at ∼ - 4 and ∼ - 1 eV , in which the latter peak shifts with increasing emission angle by ∼ 300 meV . The Ce 4f states have the negligibly small intensity near E F , reflecting the minor contribution from Ce 4f electrons to the metallic ground state of CeTe 2 . This implies that Te(1) 5p and Ce 5d electrons are involved in the CDW formation in CeTe 2 .

Charge-density wave gap and Ce4fstates inCeTe2observed by photoemission spectroscopy

The electronic structure of an $f$-electron charge-density-wave (CDW) system, $\mathrm{Ce}{\mathrm{Te}}_{2}$, has been investigated using high-resolution angle-resolved photoemission spectroscopy (ARPES). Two gaps of $\ensuremath{\sim}100$ and $\ensuremath{\sim}500\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ have been observed both along $\ensuremath{\Gamma}X$ and $\ensuremath{\Gamma}Y$, implying the $2\ifmmode\times\else\texttimes\fi{}2$ lattice deformation in the Te(1) sheets with the CDW gap of $\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. By employing the fine-structure (FS) resonance, the experimental Ce $4f$ ARPES spectra have been measured. The FS resonance ARPES shows a typical two-peak structure with the peaks at $\ensuremath{\sim}\ensuremath{-}4$ and $\ensuremath{\sim}\ensuremath{-}1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, and the weight shift in the latter peak in contrast to the traditional giant resonance. The Ce $4f$ states have the negligibly small intensity near ${E}_{\mathrm{F}}$, reflecting the minor contribution from Ce $4f$ electrons to the metallic ground state of $\mathrm{Ce}{\mathrm{Te}}_{2}$. This study reveals that the carriers near ${E}_{\mathrm{F}}$ should have mainly the Te(1) $5p$ and Ce $5d$ character, but that only the Ce $5d$ bands cross ${E}_{\mathrm{F}}$.

The fine structure of S and S− measured with the photodetachment microscope

Photodetachment microscopy of a beam of 32S− ions makes it possible to measure the detachment thresholds corresponding to different fine-structure levels of the negative ion S− and the neutral atom S. The electron affinity of sulfur, at 2.077 eV, is well suited for detachment by a tunable dye laser, which provides a third way of measuring neutral S fine structure, besides VUV spectroscopy of S I lines and direct fine-structure resonance spectroscopy. The fine-structure intervals are found to be 48 353.52(34) m−1 for the 2P1/2 − 2P3/2 energy difference in S−, and 39 605.87(32) m−1 for the 3P1 − 3P2 one in S (with expanded uncertainties), consistent with an independent measurement of the 3P0 − 3P1 interval. The new recommended electron affinity for isotope 32 of sulfur is 1675 297.60(42) m−1, or 2.077 104 18(71) eV.

Anomalous scattering in structural chemistry and biology¶

The uses of X-ray anomalous scattering in crystal structure analysis have undergone a major expansion due to the refinement and ease of availability of the necessary X-ray instrumentation and methods. The structural chemistry and biology fields span a similar suite of technical needs but with widely differing molecular systems. The innate synergies between the two research fields brought two of the authors (JRH and VK) together at an Erice Summer School on Synchrotron Radiation in Crystallography in 1985 and took them into a collaboration spanning already 20 years. The authors’ wide perspectives are therefore, if not unique, perhaps rather rare. Thus the breadth of coverage of this review is unusual. However, there are two excellent books on anomalous scattering and its uses that have been published covering the periods up to 1975 and 1994 [S. Ramaseshan, S.C. Abrahams (Eds). Anomalous Scattering, Munksgaard, Copenhagen (1975); G. Materlik, C.J. Sparks, K. Fischer (Eds). Resonant Anomalous X-ray Scattering: Theory and Applications, North Holland, Amsterdam (1994)]. As the number of examples of applications in structural biology are now so many it has only been possible to select some illustrative examples but with surveys of trends. In addition though, the development of the methodologies is described in more detail. The structural chemistry applications in, for example, microporous materials, superconductors and magnetic materials is expanding fast but still at a stage where we could attempt to provide a detailed coverage of results, which we have done. Anomalous scattering results on locating metal atoms can also be compared with other technique results and so sections on X-ray Absorption Spectroscopy (XAS), Diffraction Anomalous Fine Structure (DAFS), neutron diffraction and Nuclear Magnetic Resonance (NMR) applications are described where they relate to metal atom location and local structure. Finally anomalous scattering has also been very useful to help develop the modern synchrotron Laue method for quantitative crystal structure analysis, which is also briefly described. ¶Dedicated to Professor Durward W. J. Cruickshank, FRS, Emeritus Professor of Chemistry, The University of Manchester, on the occasion of his 82nd Birthday, 7 March 2006. Durward is an inspiration to us all as a scientist with many fine contributions spanning nearly 60 years, as well as a friend, mentor and colleague to several of us for many years. Contents Introduction 246 1. Brief resume of anomalous scattering 252 1.1.Principles 252 1.2.Different nomenclatures in use for the anomalous scattering coefficients 255 1.3.Some crystal symmetry and diffraction data measurement key facts 258 1.4.Absolute structure: the key definitions 260 2. Some historical notes: the absolute configuration of (R, R)-(1)-tartaric acid was determined by J. M. Bijvoet and colleagues (1951) 262 3. The use of anomalous scattering in structural chemistry 264 3.1.Introduction to site-specific, neighbouring element and valence contrast experiments 264 3.2.Overview of neighbouring element and valence contrast experiments 265 3.3.Applications of anomalous scattering to particular classes of materials 277 3.4.Potential applications of anomalous dispersion in powder diffraction structure solution de novo 290 3.5.The determination of the absolute configuration or hand of smaller molecules using crystallography 292 4. The use of anomalous scattering in structural biology 293 4.1.Previous reviews of the uses of anomalous scattering in protein crystallography especially SR 293 4.2.The location of the anomalous scatterers 296 4.3.MIR, SIROAS and MAD phasing 296 4.4.The recent growth of Single-wavelength Anomalous Dispersion(SAD) phasing 299 4.5.Identification of metals in metalloproteins (Mn, Zn, Cu, Ca) and ions (Cl − ,) in proteins including case studies 307 4.6.Instrumentation case study: line 10 at the SRS 309 5. Use of anomalous scattering derived structural details to help develop the Laue method 311 6. Complementary methods 314 6.1.XAS 314 6.2.Diffraction Anomalous Fine Structure Analysis (The DAFS method) 317 6.3.Neighbouring atom contrast by neutron diffraction methods 319 6.4.Magnetic resonance spectroscopy 320 7. Concluding remarks 323 Acknowledgements 324 References 325 Subject index 333

Resonance Fine Structure of Electromagnetic Waves in a Dielectric Sphere

Resonance Fine Structure of Electromagnetic Waves in a Dielectric Sphere

Dielectric and pyroelectric properties of poly[2,3-bis(trifluoromethyl)norbornadiene

The fluoropolymer poly[2,3-bis(trifluoromethyl)norbornadiene] (poly(BTFMND)) has been synthesized via ring-opening metathesis polymerization, using initiators based on W, Mo or Ru compounds or via variations of the Schrock-type initiator Mo(CHR)(N-2,6-C 6 H 3 -i-Pr 2 )(OR′) 2 (R = CMe 3 , CMe 2 Ph; R′ = CMe 3 , CMe(CF 3 ) 2 ), giving poly(BTFMND) with controllable proportions of trans -vinylene units. Analysis of the 13 C nuclear magnetic resonance fine structure establishes that the high- trans (> 98%) polymer is 92% tactic and the high- cis (> 98%) polymer is 75% tactic, but these methods cannot determine whether the material is predominantly isotactic or syndiotactic. Dielectric and thermally stimulated current measurements have been performed and give relaxed permittivities % strongly dependent on trans content, ranging from above 40 for the 98% trans material through 15 for the 54% trans polymer to 6 for 98% cis polymer. The significantly higher permittivity above T g for the high- trans material than for the 54% trans polymer and the significantly reduced value for the 98% cis polymer suggest that both the high- cis and high- trans materials have syndiotactic structures. The total polarization for free films of 98% trans poly(BTFMND) saturates at about 20 mC m −2 , with a pyroelectric coefficient approaching 6 μ C m −2 K −1 above poling fields of 200 MV m −1 . These usefully high values combined with low dielectric loss in its glassy state at ambient temperatures indicate an excellent material for potential use as a pyroelectric transducer, with a figure of merit comparable with or better than that of poly(vinylidene fluoride).

Measurement of cross sections for 12C + 14C reaction at subbarrier energies

The partial cross sections for the 12C + 14C reaction have been determined in the energy range E c.m. = 5–8 MeV by measuring, with an HPGe detector, the yields of the characteristic γ-rays emitted from the residual nuclei. Comparison of the partial cross sections with those of the 13C + 13C reaction shows that the two reactions proceed mainly via the compound-nucleus formation and subsequent statistical evaporation of particles. The total fusion cross section is well described by the optical-model calculation using standard parameters. A small enhancement observed in the total fusion cross section at E c.m. ⋍ 6 MeV , is correlated with the E x = 25.35 MeV, Γ = 1.75 MeV fine-structure resonance observed in the γ + 26Mg photonuclear reaction.

On the origin of the resonance Raman γ1 dispersion and fine structure of PtBr

The standard preparative route to [Pten 2][Pten 2Br 2](ClO 4) 4 (PtBr, where en = H 2NCH 2CH 2NH 2) results in Cl − impurities in the product. A study of resonance Raman (RR) spectra of PtBr as a function of chloride ion doping illustrates that the 166 cm −1 component of the RR spectrum corresponds to the chain axis ν 1 mode. Previously reported ν 1 dispersion and fine structure and several other resonance enhanced defect vibrations are shown to result from chloride doping of the PtBr solid.

Fine structure of resonance at Ex~ 14 MeV in 40Ca.

The inelastic scattering of protons by $^{40}\mathrm{Ca}$ leading to a resonance at ${E}_{x}$\ensuremath{\sim}14 MeV was studied at an incident energy of 65.1 MeV with an energy resolution of 23 keV. The resonance was found to consist of many discrete states, most of which were ${2}^{+}$ states, and exhausted 8% of the energy-weighted sum rule. Octupole strength of 1.8% of the energy-weighted sum rule was found, 4 times smaller than that observed in electron scattering.

The sub-Coulomb 12C + 12C resonances in a microscopic 12C+ 12C,α+ 20Ne, 8Be+ 16O cluster basis

The low- J resonances in the Coulomb barrier region of the 12 C+ 12C system are investigated in the framework of a microscopic cluster model basis including 12C+ 12C, α+ 20Ne, and su8 Be+ 16O fragment decompositions. Calculations are carried out in an orthogonality condition model approximation in which Pauli-forbidden components are properly excluded from the basis but in which the interaction among cluster fragments is approximated by a local potential, obtained from a gaussian NN interaction by a folding procedure leading to both spherical and Q · Q terms. Only minor adjustments of overall strength and fall-off parameters are introduced to gain a consistent picture of the low-energy spectrum in the separate rearrangement channels. The basis includes cluster relative motion excitations with oscillator quanta from 12 to 20 and is not quite rich enough to give a detailed quantitative comparison between theory and experiment. Predicted excitation energies are too high by ~ 3 MeV and predicted 12C partial widths are too small to indicate a well-developed surface-peaked molecular character; but it does appear possible to identify a 5 MeV region as the potential seat of the 0 +, 2 +, 4 + resonances. The number and approximate spacing of the resonance fine structure components are in agreement with experiment.

Transmission and reflection of low-energy electrons at the surface barrier of a metal

LEED calculations are presented which indicate that the emergence of a non-specular beam is accompanied with a surface resonance fine structure in the intensity of the specular beam. It is shown that the fringes of the fine structure are arranged in a Rydberg series having the constant 1/16 Rydbergs and terminating at the energy of emergence. The resonances are caused by reflections of electrons between the image potential before the metal surface on one side and the bulk of the metal on the other. The resolving power required for recording the fine structure is discussed and the calculated fine structure is compared with three electron scattering experiments.

Spin–Lattice Coefficients of Gd3+ in CdF2

AbstractEPB spectra of Gd3+ in CdF2 under uniaxial stress were observed and the spin–lattice coefficients of second and fourth order were measured. The measurements were performed in X band in the temperature range 77 to 300 K. Experimental data show that the fourth order term gives an important contribution to the shift of the fine structure resonance lines. Comparison with the results of other authors at different frequencies does not reveal a frequency dependence. Also a temperature dependence of the spin–lattice coefficients is not found. From the value of the coefficient Clg responsible for the symmetric deformation it is deduced that the temperature changes of B are due to thermal expansion.

Effect of Fine Structure on Nucleon Transfer to Analog States

We extend our previous distorted-wave Born-approximation treatment of reactions of the form $A(d,p)B$ (in which $B$ is an unbound state) to include the case where $B$ is (a) dissolved into a fine structure of resonances that may overlap strongly, and (b) unstable against emission of other particles in addition to the transferred particle $n$. We assume that the reaction is strongly peripheral and goes through the $n+A$ channel of $B$ via the $\mathrm{np}$ interaction. We discuss the cross section for an experiment in which only particle $p$ is detected, while the decay products of $B$ are not observed or identified. For an isobaric-analog resonance we find that the cross section is proportional to ${\ensuremath{\Gamma}}_{n}cos2({\ensuremath{\delta}}_{N}+\ensuremath{\varphi})$, where ${\ensuremath{\Gamma}}_{n}$ is the $n$ escape width, ${\ensuremath{\delta}}_{N}$ is the nuclear background phase shift, and $\ensuremath{\varphi}$ is the asymmetry phase. The cross section is entirely determined by the gross-structure parameters of the resonance, and does not depend on the nature of the fine structure. For the reaction $^{92}\mathrm{Mo}(d,n)$ to ${d}_{\frac{5}{2}}$ (8.40-MeV), ${s}_{\frac{1}{2}}$ (9.33-MeV), and ${d}_{\frac{3}{2}}$ (9.91-MeV) analog states, we find that the effect of ${\ensuremath{\delta}}_{N}+\ensuremath{\varphi}$ is negligible.

Fine structure and neutron decay of the isobaric analogue resonances

The mechanism of the distribution of an isobaric analogue resonance over its fine structure peaks is studied in the frame of the shell-model theory of nuclear reactions. A two-channel model is constructed, where the isobaric analogue doorway state is dominated by the entrance proton channel which, in turn, is coupled to the outgoing neutron channel only via complicated shell-model states. The energy averages of the differential elastic scattering, total and reaction cross sections are calculated. It is shown that these averages do not display the same resonance energies and widths, unless the background of the (p, n) cross section reaches its maximum value. This holds in spite of the fact that the diagonal and off-diagonal S-matrix elements have the same poles. The elastic, scattering and total cross sections in the absence of the isobaric analogue resonance are studied from a microscopic point of view and the connection with the phenomenological optical-model treatment is given. The extraction of the spectroscopic factor from the experimental data is discussed. The fluctuations of the differential elastic scattering cross section around its average are investigated. The distribution of the fine structure resonance parameters is derived for overlapping as well as isolated peaks; the results are compared with the experimental data obtained at Duke University for the reaction 40Ar(p, p)40Ar.