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Magnetic Circular Dichroism (magnetic + circular_dichroism)
Kinds of Magnetic Circular Dichroism Selected AbstractsMagnetic Materials: X-Ray Magnetic Circular Dichroism Picks out Single-Molecule Magnets Suitable for Nanodevices (Adv. Mater.ADVANCED MATERIALS, Issue 2 20092/2009) The surface sensitivity of X-ray magnetic circular dichroism in extreme conditions has been exploited to investigate the first layers of bulk single-molecule magnets (SMMs), as reported by Roberta Sessoli and co-workers on p. 167. Striking differences have emerged between two classes of SMM having different structural constraints, thus highlighting the importance of molecular design in the realization of molecular spintronic devices. [source] X-Ray Magnetic Circular Dichroism Picks out Single-Molecule Magnets Suitable for NanodevicesADVANCED MATERIALS, Issue 2 2009Matteo Mannini The surface sensitivity of X-ray Magnetic Circular Dichroism in extreme conditions is exploited to investigate the first layers of bulk single-molecule magnets (SMM). Striking differences emerge between two classes of SMM with different structural constraints, thus highlighting the importance of molecular design in the realization of molecular spintronic devices [source] Magnetic Circular Dichroism and Absorption Spectra of Phosphinidene in Noble-Gas MatricesCHEMINFORM, Issue 17 2005Jeremy J. Harrison Abstract For Abstract see ChemInform Abstract in Full Text. [source] Electronic Structure, Spectra, and Magnetic Circular Dichroism of Cyclohexa-, Cyclohepta-, and CyclooctapyrroleCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2005Alexander Gorski Abstract Three recently obtained expanded porphyrins represent nice examples of compounds for which the electronic and spectral properties can be predicted from symmetry considerations alone. Perimeter-model-based theoretical analysis of the electronic structure of doubly protonated cyclo[6], cyclo[7], and cyclo[8]pyrrole leads to the anticipation of qualitatively the same electronic absorption and magnetic circular dichroism patterns for all three compounds. These predictions are fully confirmed by experiments, as well as DFT and INDO/S calculations. Due to a characteristic pattern of frontier molecular orbitals, a degenerate HOMO and a strongly split LUMO pair, the three cyclopyrroles show comparable absorption intensity in the Q and Soret regions. Magnetic circular dichroism spectra reveal both A and B Faraday terms, of which the signs and magnitudes are in remarkably good agreement with theoretical expectations. The values of the magnetic moments of the two lowest degenerate excited states have also been obtained. [source] Magnetic circular dichroism at transition metal L2,3 edges in D03 -type (Fe1- xMnx)3Al alloysJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Kazuo Soda We have measured magnetic circular dichroism (MCD) spectra at the transition-metal L2,3 edges in D03 -type (Fe1- xMnx)3Al in order to investigate their local magnetic moments. The analysis of the spectra shows that Fe has moments much larger than Mn, whose moment is ferromagnetically coupled with the Fe one. This does not lend support to the antiferromagnetic mechanism proposed for the reduction in magnetization as well as a large Mn moment predicted for x = 1/3. The evolution of satellites found in the Mn spectrum with x increased suggests that the change in the electronic state may result in the magnetization reduction. [source] Application of Synchrotron Radiation Techniques for Model Validation of Advanced Structural Materials,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Annick Froideval Abstract Synchrotron radiation techniques represent powerful tools to characterize materials down to the nanometer level. This paper presents a survey of the state-of-the-art synchrotron-based techniques which are particularly well-suited for investigating materials properties. Complementary X-ray absorption techniques such as extended X-ray absorption fine structure (EXAFS), X-ray magnetic circular dichroism (XMCD), photoemission electron microscopy (PEEM) are used to address the individual local atomic structure and magnetic moments in Fe,Cr model systems. The formation of atomic clusters/precipitates in such systems is also investigated by means of scanning transmission X-ray microscopy (STXM). Such advanced analytical techniques can not only offer valuable structural and magnetic information on such systems, they can also serve for validating computational calculations performed at different time and length scales which can help improve materials lifetime predictions. [source] Magnetic and Structural Investigation of ZnSe Semiconductor Nanoparticles Doped With Isolated and Core-Concentrated Mn2+ IonsADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Christina Graf X-Ray magnetic circular dichroism (XMCD) experiments on diluted magnetic semiconductor nanocrystals (2,7,nm) are reported in order to study their local electronic structure and magnetic properties. ZnSe nanoparticles containing either single manganese ions (Mn2+) distributed in the lattice of the entire particle or a MnSe core in the center are prepared using high temperature approaches. The Mn2+ concentration is varied between less than one to several tens of manganese ions per nanocrystal. For all samples it is shown that the Mn2+ is exclusively present in the bulk of ZnSe nanoparticles with no evidence for oxidation to higher Mn-oxidation states. The magnetic ions are highly polarized inside the nanocrystals reaching about 80% of the theoretical value of a pure d5 state under identical conditions for the case of isolated manganese ions. Nanocrystals with a MnSe core ZnSe shell structure reach <50% of this value. Thus, their polarization is significantly more hindered, which is due to the significantly enhanced Mn,Mn interactions and a more distorted crystalline lattice. In contrast, no coupling between the manganese centers is observed in the nanoparticles doped samples with low concentrations of Mn2+, indicating that these ions are isolated in the bulk of the nanoparticles. [source] The Quest for Nanoscale Magnets: The example of [Mn12] Single Molecule MagnetsADVANCED MATERIALS, Issue 43 2009Guillaume Rogez Abstract Recent advances on the organization and characterization of [Mn12] single molecule magnets (SMMs) on a surface or in 3D are reviewed. By using nonconventional techniques such as X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM), it is shown that [Mn12]-based SMMs deposited on a surface lose their SMM behavior, even though the molecules seem to be structurally undamaged. A new approach is reported to get high-density information-storage devices, based on the 3D assembling of SMMs in a liquid crystalline phase. The 3D nanostructure exhibits the anisotropic character of the SMMs, thus opening the way to address micrometric volumes by two photon absorption using the pump-probe technique. We present recent developments such as µ-SQUID, magneto-optical Kerr effect (MOKE), or magneto-optical circular dichroism (MOCD), which enable the characterization of SMM nanostructures with exceptional sensitivity. Further, the spin-polarized version of the STM under ultrahigh vacuum is shown to be the key tool for addressing not only single molecule magnets, but also magnetic nano-objects. [source] Magnetic Materials: X-Ray Magnetic Circular Dichroism Picks out Single-Molecule Magnets Suitable for Nanodevices (Adv. Mater.ADVANCED MATERIALS, Issue 2 20092/2009) The surface sensitivity of X-ray magnetic circular dichroism in extreme conditions has been exploited to investigate the first layers of bulk single-molecule magnets (SMMs), as reported by Roberta Sessoli and co-workers on p. 167. Striking differences have emerged between two classes of SMM having different structural constraints, thus highlighting the importance of molecular design in the realization of molecular spintronic devices. [source] X-ray magnetic circular dichroism measurements using an X-ray phase retarder on the BM25 A-SpLine beamline at the ESRFJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2010Roberto Boada Circularly polarized X-rays produced by a diamond X-ray phase retarder of thickness 0.5,mm in the Laue transmission configuration have been used for recording X-ray magnetic circular dichroism (XMCD) on the bending-magnet beamline BM25A (SpLine) at the ESRF. Field reversal and helicity reversal techniques have been used to carry out the measurements. The performance of the experimental set-up has been demonstrated by recording XMCD in the energy range from 7 to 11,keV. [source] Energy-dispersive X-ray absorption spectroscopy at LNLS: investigation on strongly correlated metal oxidesJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2010Júlio C. Cezar An energy-dispersive X-ray absorption spectroscopy beamline mainly dedicated to X-ray magnetic circular dichroism (XMCD) and material science under extreme conditions has been implemented in a bending-magnet port at the Brazilian Synchrotron Light Laboratory. Here the beamline technical characteristics are described, including the most important aspects of the mechanics, optical elements and detection set-up. The beamline performance is then illustrated through two case studies on strongly correlated transition metal oxides: an XMCD insight into the modifications of the magnetic properties of Cr-doped manganites and the structural deformation in nickel perovskites under high applied pressure. [source] Origin of the X-ray magnetic circular dichroism at the L -edges of the rare-earths in RxR1,x,Al2 systemsJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2009Jesús Chaboy An X-ray magnetic circular dichroism (XMCD) study performed at the rare-earth L2,3 -edges in the RxR1,x,Al2 compounds is presented. It is shown that both R and R, atoms contribute to the XMCD recorded at the L -edges of the selected rare-earth, either R or R,. The amplitude of the XMCD signal is not directly correlated to the magnetization or to the value of the individual (R, R,) magnetic moments, but it is related to the molecular field acting on the rare-earth tuned in the photoabsorption process. This result closes a longstanding study of the origin of the XMCD at the L -edge of the rare-earths in multi-component systems, allowing a full understanding of the exact nature of these signals. [source] XAS and XMCD under high magnetic field and low temperature on the energy-dispersive beamline of the ESRFJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2007O. Mathon The present paper demonstrates the feasibility of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) under high magnetic fields up to 26,T and low temperatures down to 5,K on the ID24 energy-dispersive XAS beamline of the ESRF. The pulsed magnetic field set-up, entirely developed at the ESRF, is described as well as the beamline set-up, the synchronization and the measurement procedure. It allows field strengths up to 30,T. Finally, as an example, we report a recent XMCD study at the Re L2 and L3 absorption edges of the double perovskite Sr2CrReO6. [source] Magnetic X-ray absorption fine structure for Ni,Mn alloysJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2003T. Miyanaga Magnetic X-ray absorption fine-structure (XAFS) spectra have been measured for Ni,Mn alloys. The magnetic XAFS in the near-edge region (X-ray absorption near-edge structure, XANES) and X-ray magnetic circular dichroism (XMCD) of the Mn and Ni K -edge for Ni1,xMnx (x = 0.25, 0.24 and 0.20) show that (i) the local magnetic structure around the Mn atom is quite different from that around the Ni atom, and (ii) the peak intensity in the magnetic XANES of the Mn K -edge depends on the magnetization of the sample in contrast to the Ni K -edge. The Mn K -edge magnetic EXAFS (extended XAFS) for Ni0.76Mn0.24 is also measured. The second and fourth peaks in the Fourier transform are observed to be enhanced in comparison with the non-magnetic EXAFS, indicating that the second- and fourth-shell Ni atoms are replaced by Mn atoms due to heat treatment (atomic ordering). Semi-relativistic theoretical calculation explains the observed magnetic EXAFS. [source] X-ray magnetic circular dichroism imaging with hard X-raysJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2001K. Sato X-ray polarization-contrast images resulting from X-ray magnetic circular dichroism (XMCD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders, and a high-spatial-resolution X-ray charge-coupled-device detector. The sample used was a hexagonal-close-packed cobalt polycrystal foil having a thickness of about 4,µm. The X-ray polarization-contrast image resulting from XMCD was observed at a photon energy of 10,eV above the cobalt K -absorption edge (7709,eV). The observed contrast in the image was reversed by inversion of the magnetic field. Furthermore, the contrast was reversed again at a photon energy of 32,eV above the cobalt K -absorption edge. [source] Theory of resonant X-ray emission spectroscopyJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001A. Kotani A short review is presented of recent topics in resonant X-ray emission spectroscopy (RXES), especially of the polarization dependence of RXES in d and f electron systems. Polarization-dependent RXES provides important information on the symmetry of electronic states. A scattering-angle dependence in the fluorescence yield of rare-earth metals, RXES in polarized and depolarized configurations of TiO2, and the magnetic circular dichroism in RXES of ferromagnetic systems are discussed together with typical experimental data. [source] Anisotropic features in XMCD spectraJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Shin-ichi Nagamatsu The angular dependent K -edge X-ray magnetic circular dichroism (XMCD) spectra based on the semi-relativistic full multiple scattering theory are discussed, where 2-spinor formalism is used to describe spin-orbit coupling. So far most of theoretical approaches have been limited to the simplest case where the circularly polarized X-ray propagation coincides with the direction of the magnetic field. Here we discuss more general cases, using the above theoretical approaches. We separately discuss atomic, single and full multiple scattering XMCD spectra; in particular anisotropic features of them are studied in detail. [source] Electronic states in Cu2MnX (X = Al, In and Sn) Heusler alloy studied by XMCD and multiple scattering calculationsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Shigeaki Uemura X-ray magnetic circular dichroism (XMCD) has been measured at Mn and Cu K-edge in Cu2MnX (X = Al, In, and Sn) Heusler alloy. The Mn K -edge spectrum shows a dispersion-type profile and the Cu K -edge resembles the Mn spectrum, which suggests that polarization of the p unoccupied bands originates commonly in Mn 3d states. To reproduce the observed spectrum by full multiple scattering calculations, Madelung potential has been taken into account. Charge redistribution is an important factor for the electronic structure in Cu2MnX Heusler alloy. [source] Magnetic circular dichroism at transition metal L2,3 edges in D03 -type (Fe1- xMnx)3Al alloysJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001Kazuo Soda We have measured magnetic circular dichroism (MCD) spectra at the transition-metal L2,3 edges in D03 -type (Fe1- xMnx)3Al in order to investigate their local magnetic moments. The analysis of the spectra shows that Fe has moments much larger than Mn, whose moment is ferromagnetically coupled with the Fe one. This does not lend support to the antiferromagnetic mechanism proposed for the reduction in magnetization as well as a large Mn moment predicted for x = 1/3. The evolution of satellites found in the Mn spectrum with x increased suggests that the change in the electronic state may result in the magnetization reduction. [source] High-field optically detected EPR and ENDOR of semiconductor defects using W-band microwave Fabry,Pérot resonators,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005J.-M. Spaeth Abstract The designs of W-band (,95 GHz) Fabry,Pérot microwave resonators for optically detected EPR and ENDOR using the magnetic circular dichroism of the optical absorption (MCDA) as well as for photo-luminescence-detected EPR are briefly described. We report on the first MCDA-detected high-field EPR/ENDOR investigation of the paramagnetic EL2+ defect in semi-insulating GaAs. The higher-order effects, which prevented the unambiguous analysis of previous MCDA-detected K-band EPR/ENDOR experiments could be suppressed in W-band. The analysis of the ENDOR spectra showed that an extremely precise alignment of the samples is necessary. The paramagnetic El2+ defect turned out to be an As antisite defect, which has four almost equivalent nearest 75As neighbours differing less than 1.5% in the superhyperfine interactions suggestive of an isolated As antisite, while the third 75As shell (fifth neighbour shell) is clearly of lower symmetry than expected for an isolated As antisite. We discuss as a possible solution to this paradoxical situation that EL2+ is an isolated antisite at room temperature, which at low temperature, where all magnetic resonance experiments are performed, associates itself with shallow acceptors such as ZnGa, more than two nearest neighbour distances away. According to recent theoretical calculations, such ,loose' complexes with binding energies between 0.01 eV and 0.05 eV and disturb the equivalence of the nearest neighbour superhyperfine (shf) interactions less than 1.5%. Also, W-band EPR was measured using the photo-luminescence for detection to investigate P dopants in 6H-SiC. Copyright © 2005 John Wiley & Sons, Ltd. [source] Experimental and theoretical study of the magnetic properties and XMCD spectra of Ru clusters deposited on Fe/Cu(001)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2010J. Minár Abstract We present results of an experimental study of magnetic properties of small Ru clusters deposited on a thin Fe film grown on Cu(001) surface. X-ray magnetic circular dichroism (XMCD) measurements show finite spin and orbital moments of Ru dimers and trimers, however a magnetic moment for a Ru monomer has been not observed. A corresponding theoretical study based on the fully relativistic multiple scattering KKR method is presented. Detailed theoretical analysis has been performed to explain the experimental findings. In particular a direct comparison of the calculated XMCD with the experiments suggests diffusion into the surface as a possible reason for the apparent quenching of the spin magnetic moment for Ru monomers. [source] Magneto-optical spectroscopy of (Zn,Co)O epilayersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006W. Pacuski Abstract We present a magneto-optical study of (Zn,Co)O layers grown by molecular beam epitaxy. We observed sharp lines related to 4A2,2E intra-ionic Co2+ transitions, and to the A , B and C excitons. Intra-ionic transitions observed by absorption and photoluminescence were used to determine the values of the parameters describing the isolated Co ions, such as the easy-plane magnetic anisotropy and the g -factor of the S = 3/2 Cobalt spin. Excitonic transitions observed in reflectivity were used to determine the giant Zeeman splitting and to estimate the effective coupling ,N0(, , , ),A ,B = 0.4 eV between excitons and Cobalt spins. Due to the electron,hole exchange within the exciton, this effective spin,exciton coupling is much weaker than the exchange integrals for free carriers, estimated to be N0|, , , | , 0.8 eV, with a positive value of (, , , ) if the normal ordering of the valence band of ZnO is assumed. The Zeeman splitting of diluted samples and the magnetic circular dichroism (for a higher Co content) are proportional to the magnetization of the paramagnetic, isolated Cobalt ions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Soft X-ray absorption spectroscopy and magnetic circular dichroism study of electroless-deposited CoNiFe ternary alloy soft magnetic filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006Masahito Tanaka Abstract We studied microscopic magnetic properties of each consistent atom in boron added CoNiFe electroless-deposited soft magnetic films, which is a promising candidate for the soft magnetic underlayer of the perpendicular magnetic recording medium, by X-ray absorption spectra (XAS) and magnetic circular dichroism (MCD) measurement. It was found that various monoxides and Fe sesquioxide coexisted with the metals at the upper part of the films. The results of MCD sum rule showed the expected values of orbital angular moment ,Lz, for the film with macroscopic magnetic domain boundaries were larger than those of without domains at Co and Ni atoms and smaller at Fe atom. The appearance of macroscopic magnetic domain boundaries probably originated from the increase in ,Lz, of Co and/or Ni atoms. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis, Structures, and Optical and Electrochemical Properties of BenzoporphycenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 39 2009Daiki Kuzuhara Abstract The first facile syntheses of free-base di- and tetrabenzoporphycenes and their metal complexes are reported, based on retro-Diels,Alder reactions of the corresponding bicyclo[2.2.2]octadiene-fused porphycenes, prepared by McMurray coupling of ,,,,-diformyldipyrrole. The photophysical and electrochemical properties are analyzed based on UV/Vis absorption, magnetic circular dichroism (MCD), and fluorescence emission, lifetime and quantum yield measurements, cyclic and differential pulse voltammetry (CV and DPV) and time-dependent DFT calculations based on B3LYP geometry optimizations. Benzoporphycenes are found to be prime candidates for future use in photodynamic therapy. [source] Application of the Perimeter Model to the Assignment of the Electronic Absorption Spectra of Gold(III) Hexaphyrins with [4n+2] and [4n] ,-Electron SystemsCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009Atsuya Muranaka Dr. Abstract Expanded porphyrins: The electronic excited states of two forms of meso -hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1), such as that depicted, have been investigated by density functional calculations and magnetic circular dichroism spectroscopy to assign their low-energy excited singlet states. The electronic excited states of two forms of meso -hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1) have been investigated by density functional calculations and magnetic circular dichroism (MCD) spectroscopy, in order to assign their low-energy excited singlet states. We found that the perimeter model can be successfully applied to the interpretation of the electronic states. In the case of the neutral forms (Au2 -N, Au-N), the absorption bands observed in the NIR and visible region can be assigned to ,,,* transitions referred to as the L and B bands, respectively, analogous to the Q and Soret bands of regular porphyrins. In marked contrast with the neutral forms, the absorption bands of the reduced forms (Au2 -R and Au-R) are attributed to ,,,* transitions involving six frontier molecular , orbitals. By applying the 4N -electron perimeter model, the six orbitals are labeled as h,, h+, s,, s+, l,, and l+, while the observed absorption bands can be assigned to the S, N1, N2, P1, and P2 transitions, in order of increasing energy. [source] | ||||||||||||||||