Dependence Of Magnetic Circular Dichroism Research Articles

Magneto-optical properties of nanoparticle dispersions based on Fe-=SUB=-3-=/SUB=-O-=SUB=-4-=/SUB=-, obtained by pulse laser ablation in a liquid

The structure, optical and magneto-optical properties of colloidal solutions of iron oxide nanoparticles obtained by pulsed ablation in distilled water, both without additives and with various functional additives: gold-hydrochloric acid, silicon oxide, and polyvinylpyrrolidone, have been studied. It is shown that the main magnetic phase is magnetite Fe3O4. The size distribution of nanoparticles and the degree of their agglomeration depend on the additives. In the absence of the latter, a very wide of size distributions and strong agglomeration of particles are observed. The narrowest distribution curve with a maximum corresponding to ~7 nm and an almost complete absence of agglomeration are observed for particles synthesized in the presence of polyvinylpyrrolidone. The shape of the spectral dependence of magnetic circular dichroism, which generally corresponds to the spectrum of magnetite, undergoes some modifications for various additives, which is associated with defects in the distribution of iron ions between different positions in the crystal. Keywords: pulsed laser ablation, nanoparticles, colloidal solutions, magnetite, magnetic circular dichroism.

Магнитооптические свойства дисперсий наночастиц на основе Fe-=SUB=-3-=/SUB=-O-=SUB=-4-=/SUB=-, полученных методом импульсной лазерной абляции в жидкости

The structure, optical and magneto-optical properties of colloidal solutions of iron oxide nanoparticles obtained by pulsed ablation in distilled water, both without additives and with various functional additives: gold-hydrochloric acid, silicon oxide, and polyvinylpyrrolidone, have been studied. It is shown that the main magnetic phase is magnetite Fe3O4. The size distribution of nanoparticles and the degree of their agglomeration depend on the additives. In the absence of the latter, a very wide of size distributions and strong agglomeration of particles are observed. The narrowest distribution curve with a maximum corresponding to ~ 7 nm and an almost complete absence of agglomeration are observed for particles synthesized in the presence of polyvinylpyrrolidone. The shape of the spectral dependence of magnetic circular dichroism, which generally corresponds to the spectrum of magnetite, undergoes some modifications for various additives, which is associated with defects in the distribution of iron ions between different positions in the crystal.

Analysis of optical and magnetooptical spectra of Fe5Si3 and Fe3Si magnetic silicides using spectral magnetoellipsometry

The optical, magnetooptical, and magnetic properties of polycrystalline (Fe5Si3/SiO2/Si(100)) and epitaxial Fe3Si/Si(111) films are investigated by spectral magnetoellipsometry. The dispersion of the complex refractive index of Fe5Si3 is measured using multiangle spectral ellipsometry in the range of 250–1000 nm. The dispersion of complex Voigt magnetooptical parameters Q is determined for Fe5Si3 and Fe3Si in the range of 1.6–4.9 eV. The spectral dependence of magnetic circular dichroism for both silicides has revealed a series of resonance peaks. The energies of the detected peaks correspond to interband electron transitions for spin-polarized densities of electron states (DOS) calculated from first principles for bulk Fe5Si3 and Fe3Si crystals.

Temperature dependence of magnetic circular dichroism of X-ray emission for rare-earth compounds

We have measured the temperature dependence of magnetic circular dichroism (MCD) of 4d–4f resonant X-ray emission for Gd and DyCo 2. A parameter to correct the self-absorption effect for the MCD spectra is introduced to estimate the 4f magnetization. However, the discrepancy between the magnetizations estimated from the MCD measurement and the SQUID measurement still remains, especially for DyCo 2 at the low temperature.

Angular and temperature dependence of the magnetic circular dichroism in4dcore-level photoemission from Gd(0001)

We present experimental and theoretical results for the angular and temperature dependence of magnetic circular dichroism in Gd $4d$ core-level photoelectron emission from a Gd(0001) surface in both normal and off-normal directions and with azimuthal variation. Two theoretical approaches are used to model this data: a single electron theory with full multiple scattering of the outgoing photoelectron and a full-relativistic many-electron theory with single scattering only. Thermal effects due to atomic vibrations and the excitation of initial-state multiplets are also included. For normal emission, we find smooth free-atom-like angular variations in emission intensity, while for off-normal emission, deviations from a purely atomic model due to photoelectron diffraction effects are seen that are well predicted by photoelectron diffraction theory. We also compare dichroism measurements using two different approaches (fixed magnetization with variable light helicity and fixed light helicity with rotated sample magnetization) and find significant differences between them that are also well predicted by theory. The angular dependence of magnetic circular dichroism for a specific set of Gd $4d$ multiplet states has also been measured with high electron energy resolution (\ensuremath{\leqslant}100 meV), permitting a state-specific decomposition of the dichroism. Such state-resolved dichroism is found to be very well described by our many-electron approach. Finally, we present temperature-dependent magnetic circular dichroism (MCD) data for $4d$ emission that should permit the study of near-surface magnetic phase transitions, and discuss the relationship of such MCD measurements to magnetization. Some future prospects and applications of such core-photoemission dichroism measurements are discussed.

Orientation effects in soft X-ray magnetic circular dichroism

Abstract The orientation dependence of magnetic circular dichroism (MCD) at soft X-ray absorption edges is discussed for paramagnetic 3d transition metal systems using ligand-field atomic multiplet calculations. Previous calculations have used a magnetic orientation along the z axis of the transition metal site. In the present work, three orientation directions are calculated: [001], [110] and [111]. Also an at-random spectrum is calculated which represents the actual situation for 3d transition metals in metalloproteins. The systems investigated can be divided into three classes based on the difference between the MCD effect for the different orientations. The first class contains spherical systems like, for instance, Fe 3+ (d 5 ) systems in O h and T d symmetries and Ni 2+ in O h symmetry. The differences between different orientations in these systems are small, or even absent. The second class contains first-class systems with a distorted local symmetry like Fe 3+ in D 2d symmetry and Ni 2+ in D 4h symmetry. The differences between the different orientations can be quite strong and result from differences in polarization for the left and right circularly polarized absorption spectra. The third-class systems exhibit relatively large zero-field splittings. The differences are very strong and are a result of the interaction between the zero-field splittings and the applied magnetic field. An example is Fe 2+ in D 2d symmetry.

Magnetic circular and linear dichroism saturation studies: Determination of the ‘‘crystal field’’ splitting in krypton and xenon matrix-isolated iron atoms

The site symmetry and magnitude of the crystal field splitting of metal atoms trapped in rare gas matrices may be determined by a combination of the temperature and magnetic field dependence of magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD). General theoretical expressions are derived for the MCD and MLD considering the Zeeman effect and the matrix (i.e., crystal field) as perturbations on the free atom ‖JMJ〉 states. These expressions are applied to the observed MCD and MLD T- and B-saturation curves for Fe atoms isolated in krypton and xenon matrices in the range 0–1.5 T and 2.3–22 K. An octahedral crystal field model accounts well for all four independent sets of data (MCD vs B, MCD vs 1/T, MLD vs B2, and MLD vs 1/T2) for two different, isolated electronic transitions. A crystal field parameter of +0.06±0.05 cm−1 has been determined, corresponding to an overall electronic ground-state splitting of 3.2±2.5 cm−1. This splitting is less than the optical bandwidth and is shown to be consistent with previous studies of rare gas matrix-isolated Fe atoms by Mössbauer and laser-excited emission spectroscopies.

Polar Kerr effects and Magnetic circular dichroism in YBa 2Cu 3O 7−δ films

We have performed high-sensitivity magneto-optical measurements using alternating fields of small amplitude. With this technique we measured both polar Kerr effects and magnetic circular dichroism in YBa 2Cu 3O 7−δ films at photon energies between 1.2 eV and 2.7 eV. The detection of three correlated effects enabled us for the first time to determine the complex Verdet constant of Yba 2Cu 3O 7−δ and to make an internal-consistency check. The temperature dependence of magnetic circular dichroism is linear at all investigated photon energies and we find no hints for a temperature dependence of paramagnetic type.

Crystalline symmetry effects in X-ray magnetic circular dichroism in angle-resolved core-level photoemission

The dependence of magnetic circular dichroism (MCD) in core-level photoemission on the experimental geometry and direction of electron emission has been studied experimentally using photoemission from the 2p and 3p levels of iron. The MCD has been measured both along emission directions of high symmetry, and along general emission directions within a single mirror plane. The observed angular variations cannot be accounted for by model calculations based on absorption, or based on angle-resolved emission into photoelectron states of a single, oriented atom. They are consistent with a model where the photoelectron states of the crystalline symmetry appropriate to couple to the detector are used.

Orientation dependence of magnetic circular dichroism in tin-doped yttrium iron garnet

Measurements are reported of optical absorption and magnetic circular dichroism (MCD), in the range of wavelength 1.0-2.7 mu m, made on tin-doped YIG with the specimen orientations (100), (110) and (111). These effects are studied at room and liquid-nitrogen temperatures. The transitions at 1.15, 1.65 and 2.00 mu m, are clearly observed in the low-temperature absorption spectrum as well as in the MCD measurements. The MCD intensities at 1.15 mu m are proportional to 1:0.85:1.03 at room temperature and to 1:0.87:1.15 at 77K respectively for the (100), (110) and (111) samples. They are also consistent with the hypothesis assumed in the theory of Leoni and Tucciarone (1972) if the differences in doping concentration among the three samples are taken into consideration.

Molecular weight dependence of magnetic circular dichroism for polystyrenes in solution

AbstractThe molecular weight dependence of the magnetic circular dichroism (MCD) for polystyrenes (PS) has been studied in various solvents by using the normalized dipole‐strength D*. The normalized MCD intensity B* is not so much affected by the molecular weight as the normalized dipole strength D+. The ratio of the Faraday parameter to the dipole strength, B*/D*, decreases as the molecular weight increases to 4,0.103 and is constant above it. The increase of the normalized D* with the increase of molecular weight is interpreted in terms of the closer approach of chromophores. These results indicate that MCD for polystyrenes is influenced by the interaction of chromophores in a polymer chain: the decrease of B*/D* comes from the increase of the interaction of chromophores. This tendency is enhanced by solvent effects on MCD.