On the Calculation of an X-Ray Natural Circular Dichroism Signal

The sequential derivation of an expression that describes an X-ray natural circular dichroism (XNCD) signal in the most general case is performed. The obtained expression is used as a basis to consider XNCD signals and their structural origins in copper metaborate CuB₂O₄ crystals at an incident radiation energy near the K absorption edge of copper and lanthanum–gallium silicate La₃Ga₅SiO₁₄ crystals at an incident radiation energy near the K absorption edge of gallium. It has been demonstrated that the measurements of circularly polarized X-ray absorption spectra in combination with corresponding first-principle calculations provide an efficient method for studying the contributions of crystallographically non-equivalent atoms to the X-ray optical activity of crystals.     

Magnetic circular dichroism and optical absorption in TmAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

The polarized spectra of absorption and magnetic circular dichroism in a TmAl₃(BO₃)₄ single crystal are studied in the region of ³ H ₆ → ³ F ₄, ³ H ₆ → ³ F ₃, and ³ H ₆ → ³ F ₂ electronic transitions in the Tm³⁺ ion. The structure of the spectra is interpreted qualitatively. It is shown that the magnetic circular dichroism of the ³ H ₆ → ³ F ₄ transition is determined by the contribution from the splitting of the ground state, whereas the magnetic circular dichroism of the ³ H ₆ → ³ F ₃ transition is governed by the contribution from the splitting of an excited state in a trigonal crystal field.     

Transition between incommensurate phases accompanied by reversal of the magnetic structure vector in CuB<Subscript>2</Subscript>O<Subscript>4</Subscript>

The incommensurate magnetic state of copper metaborate CuB₂O₄ is studied in the temperature range 2 < T < 12 K. Competition between frustrated and non-frustrated antisymmetric exchange interactions is shown to cause the magnetic structure vector to reverse at T = 10 K.     

Effect of Nitrogenation and Hydrogenation on the Magnetic Properties and Structure of the Sm<Subscript>2</Subscript>Fe<Subscript>17</Subscript> Alloy: Analysis of XMCD Data

Changes in the local magnetic and structural properties of Sm₂Fe₁₇ alloys at nitrogenation and hydrogenation of samples have been studied by the X-ray magnetic circular dichroism (XMCD) technique at the Fe K absorption edge and Sm L₃ absorption edge using synchrotron radiation. The results have been discussed in comparison with X-ray diffraction data and macroscopic vibration magnetometry measurements. The observed changes in XMCD spectra indicate a noticeable effect of nitrogenation on the local magnetic properties of sublattices of both iron and samarium, whereas hydrogenation of samples makes a small effect. The mentioned effects have been analyzed and discussed in terms of the effect of nitrogen (N) and hydrogen (H) interstitial atoms on Sm 5d and Fe 4p electronic states. The effect of nitrogenation is larger than the effect of hydrogenation because the volume expansion of the crystal lattice of initial Sm₂Fe₁₇ in the case of nitrogenation is larger than that in the case of hydrogenation. The studied local magnetization curves for samarium and iron sublattices in magnetic fields up to 17 T also indicate a strong increase in the magnetocrystalline anisotropy at nitrogenation.     

EXAFS study of copper complexes with azomethinic ligand environment

A series of copper metallochelates C₂₂H₁₈CuN₄O₂ X (X = Se, S, O) as models of active centers of natural metalloproteins have been synthesized on the basis of new azomethine ligand systems. The structure of the complexes has been studied by extended X-ray absorption fine-structure spectroscopy. It is shown that, in the metallochelates with X = Se or S, one azomethine chalcogen-containing ligand undergoes tridentate interaction with copper ions, while the other ligand is an acetate group. As a result, a complex with the N₂O₂ X environment is formed, where one of the oxygen atoms of the acetate group is at a large distance from the metal ion: R = 2.56–2.68 Å. For the metallochelate with X = O, coordination of the acetate group by a copper ion is found to be absent, and only interaction with azomethine ligands having average Cu-N/O distances R = 1.96–2.04 Å is observed.     

Magneto-optical properties of Dy<Superscript>3+</Superscript> in oxide glasses: The origin of the magneto-optical activity of <Emphasis Type="Italic">f-f</Emphasis> transitions and its anomalous temperature dependence

The temperature dependence of the absorption spectra and magnetic circular dichroism due to f-f transitions from the ⁶ H _15/2 to ⁶ F _5/2 and ⁶(F _7/2 + H _5/2) states in the Dy³⁺ ion in (Dy₂O₃-P₂O₅-SiO₂-GeO₂) and (Dy₂O₃-La₂O₃-Al₂O₃-B₂O₃-SiO₂-GeO₂) glasses and the temperature dependence of the Faraday effect were studied. The temperature dependence of the Faraday effect caused by f-d transitions was found to differ from that of the magnetic circular dichroism due to f-f transitions. It was shown that f-f transitions occur preferentially in Dy³⁺ ions associated into clusters. The origin of the paramagnetic magneto-optical activity of f-f transitions was analyzed. It was shown that the contributions to this activity can differ in value and sign and that the ratio between these contributions depends on the transition type. In some cases, this difference results in an anomalous temperature dependence of the magneto-optical activity.     

Specific features of magneto-optical spectra of Tb<Subscript>3</Subscript>Ga<Subscript>5</Subscript>O<Subscript>12</Subscript>

The spectra of magnetic circular dichroism in the range of the ⁷ F ₆→⁵ D ₄ absorption band and the spectra of magnetic circular polarization of luminescence in the range of the ⁵ D ₄→⁷ F ₅ band in the terbium-gallium garnet Tb₃Ga₅O₁₂ are studied at a temperature of 80 K. The optical transitions between the Stark sublevels of the ⁷ F ₆, ⁷ F ₅, and ⁵ D ₄ multiplets are identified based on the analysis of the magneto-optical and optical spectra. It is shown that the experimentally determined symmetry and energy of the Stark sublevels of these multiplets confirm the results of numerical calculations of the energy spectrum of the Tb³⁺ rare-earth ion in terbium-gallium garnet.     

Electronic and Magnetic States of Pr and Mn in the Pr<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> Films Studied by XANES and XMCD Spectroscopy

The spectral dependences of X-ray absorption near-edge spectroscopy (XANES) and X-ray magnetic circular dichroism (XMCD) and the field dependences of XMCD near the K edge of Mn and the L_2,3 edges of Pr in the Pr_0.8Sr_0.2MnO₃ and Pr_0.6Sr_0.4MnO₃ films at T = 90 K are studied. The spectral dependences point to a mixed valence state of Mn and Pr in the films. It is found that, as compared to XANES, XMCD is more sensitive to the valence state of Pr⁴⁺. The field dependences of XMCD point to ferromagnetic behavior of Mn ions and the Van Vleck paramagnetism of Pr ions, which makes a significant contribution to the total magnetization of the films. It is shown that as the Sr concentration increases, the XMCD intensity at the K edge of Mn increases, which indicates a growth of the total magnetic moment of the film due to an increase in the 4p–3d hybridization.     

Crystal structure and electronic states of Co and Gd ions in a Gd<Subscript>0.4</Subscript>Sr<Subscript>0.6</Subscript>CoO<Subscript>2.85</Subscript> single crystal

X-ray diffraction and X-ray absorption near edge structure (XANES) spectra have been measured at the Со K-edge and Gd L ₃-edge in GdCoO₃ and Gd_0.4Sr_0.6CoO_2.85 cobaltites. The effect of Sr substitution on the crystal structure and electronic and magnetic states of Co³⁺ ions in a Gd_0.4Sr_0.6CoO_2.85 single crystal has been analyzed. The XANES measurements at the Co K-edge have not showed a noticeable shift of the absorption edge with an increase in the concentration of Sr. This indicates that the effective valence of cobalt does not change. An increase in the intensity of absorption at the Gd L ₃-edge is due to an increase in the degree of hybridization of the Gd(5d) and O(2p) states. The effect of hole doping on the magnetic properties results in the appearance of the ferromagnetic component and in a significant increase in the magnetic moment.     

Structure and dielectric properties of solid solutions Bi7Ti4 + x W x Ta1–2x O21 (x = 0–0.5)

A number of solid solutions Bi₇Ti_{4 + x} W _x Ta_1–2x O₂₁ (x = 0–0.5) have been synthesized from oxides by solid-phase reaction. The crystal structure, the electrophysical characteristics, and the microstructure of the prepared ceramic samples have been studied. According to X-ray powder diffraction, all the compounds are single-phase with the structure of mixed-layer Aurivillius phases (m = 2.5) with the orthorhombic crystal lattice (space group I2cm, Z = 2). Temperature dependences of the relative permittivity ε(T) of the compound have been measured, from which it has been found that the Curie temperature T _C of perovskite-like oxides Bi₇Ti_{4 + x} W _x Ta_1–2x O₂₁ (x = 0–0.5) decreases linearly as substitution parameter x decreases. The activation energies of charge carriers have been found in different temperature ranges.     

Magneto-optical spectroscopy and optical detection of EPR spectra of Yb<Superscript>3+</Superscript> paramagnetic centers with cubic symmetry in single crystals <Emphasis Type="Italic">Me</Emphasis>F<Subscript>2</Subscript> (<Emphasis Type="Italic">Me</Emphasis> = Cd,Ca, Pb)

Cubic paramagnetic centers formed by Yb³⁺ impurity ions in fluorite-type crystals MeF₂ (Me = Cd, Ca, Pb) have been investigated using electron paramagnetic resonance, magnetic circular dichroism, magnetic circular polarization of luminescence, Zeeman splitting of optical absorption and luminescence lines, and optical detection of electron paramagnetic resonance. The g factors of the ²Γ₇ state in the excited multiplet ² F _5/2 of Yb³⁺ ions in Me F₂ crystals, the hyperfine interaction constant ¹⁷¹ A (¹⁷¹Yb) for the excited multiplet ² F _5/2 in the CaF₂ crystal, and the energies and symmetry properties of all energy levels of Yb³⁺ ions in MeF₂ crystals are determined. The crystal-field parameters for the crystals under investigation are calculated.     

Mechanism of magnetic ordering in Dy<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-Ni bilayer films

A mechanism for the magnetic ordering of dysprosium in Dy_1?x Ni _x -Ni bilayer films is proposed. This ordering was discovered earlier by the authors when studying magnetic circular dichroism. For x exceeding a threshold value (～0.05), the contribution from the Dy_1?x Ni _x layer in a bilayer film to the magnetic circular dichroism over the temperature range 80–300 K is approximately equal in magnitude to the magnetic circular dichroism observed in a single-layer Dy film at temperatures below the ferromagnetic phase transition temperature of Dy (～100 K). Since magnetic circular dichroism is an effect linear in magnetization, the observed effect is associated with magnetic ordering of the Dy_1?x Ni _x layer in bilayer films due to the simultaneous influence of two factors: the incorporation of Ni into the Dy layer and the influence of the continuous Ni sublayer. The ferromagnetic ordering of a dysprosium layer doped with nickel (under conditions of an atomic contact with a continuous nickel layer) was confirmed by the field dependences of the polar and longitudinal Kerr effects. It was shown that both layers in the bilayer structure are magnetized in the same direction and characterized by an anisotropy of the easy-plane type. The magnetic ordering is assumed to be due to the change in the density of states of the Dy_1?x Ni _x alloy caused by hybridization with the narrow peaks near the Fermi level characteristic of nickel.     

Magnetic properties of single crystals of a new cobaltite TbBaCo<Subscript>4</Subscript>O<Subscript>7+<Emphasis Type="Italic">x</Emphasis></Subscript>

The temperature and field dependences of the magnetization of a single crystal of a new class of layered cobaltites, TbBaCo₄O_7+x , with a structure containing a Kagomé lattice and a triangular lattice were measured. The measurements were performed on a SQUID magnetometer at temperatures in the range 2–300 K and in magnetic fields of up to 55 kOe for two field orientations. The anisotropy of the magnetization was studied, and the presence of antiferromagnetic ordering in fields H < H _c and a weak magnetic-field-induced (H > H _c ) ferromagnetic component in the low-temperature range was demonstrated. The magnetic characteristics of the initial TbBaCo₄O_7+x single crystal and the single crystal annealed in an O₂ atmosphere were compared.     

Elastic properties of La<Subscript>0.82</Subscript>Ca<Subscript>0.18</Subscript>MnO<Subscript>3</Subscript> single crystal

The temperature dependences of the velocity of longitudinal sound waves and the internal friction in a La_0.82Ca_0.18MnO₃ single crystal with the Curie temperature T _C = 181 K have been studied. As temperature decreases, the single crystal is shown to undergo the transition from the pseudocubic O* to the Jahn–Teller O’ phase at T ~ 254 K and the reverse transition from O’ to O* phase at T ~ 84 K. The velocity of sound and the internal friction in the O’ phase are found to be significantly smaller than those in the O* phase.     

Analysis of traditional Tibetan pills

Traditional Tibetan medicine starts to be a very popular complementary medicine in USA and Europe. These pills contain many elements essential for the human body. However, they might also contain heavy metals such as mercury, iron, arsenic, etc. This paper focuses on elemental composition of two Tibetan pills and investigation of forms of iron in them. X-ray fluorescence spectroscopy and neutron activation analysis identified the presence of several heavy metals such as mercury, iron and copper. M?ssbauer spectroscopy revealed the possible presence of α ? F e ₂ O ₃(hematite) and α ? F e O O H(goethite) in both of the investigated samples.     

Influence of magnetic ordering on the structural properties of dilute copper ferrites

The x-ray structural properties of samples in the CuGa_xAl_xFe_2?2x O₄ (x = 0?0.7) and CuGa_xAl_2x Fe_2?3x O₄ (x = 0?0.5) systems are studied. It is found that magnetic ordering in dilute copper ferrites affects their structural properties. It is concluded that the frustration of magnetic coupling leads to suppression of the cooperative Jahn-Teller effect in dilute copper ferrites with a frustrated magnetic structure.     

X-ray detected magnetic resonance at the Fe K-edge in YIG: Forced precession of magnetically polarized orbital components

X-ray detected magnetic resonance (XDMR) has been measured for the first time on exciting the Fe K-edge in a high-quality yttrium iron garnet film epitaxially grown on a gadolinium gallium garnet substrate. This challenging experiment required resonant pumping of yttrium iron garnet at high microwave power, i.e., in the foldover regime. X-ray magnetic circular dichroism (XMCD) was used to probe the change in the longitudinal component of the magnetization M _Z induced by the precession of magnetic moments located at the iron sites. Since XMCD at the Fe K-edge refers mostly to the equilibrium contribution of magnetically polarized 4p orbital components, XDMR at the Fe K-edge should reflect the precessional dynamics of the latter orbital moments. From the measured precession angle, we show that there is no dynamical quenching of the polarized orbital components at the iron sites in yttrium iron garnet.     

Experimental Study and Analysis of Absorption Spectra of Ni<Superscript>2+</Superscript> Ions in Nickel Orthoborate Ni<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>2</Subscript>

The results of studies of the absorption spectra of nickel orthoborate Ni₃(BO₃)₂ in the range of electronic d–d-transitions are reported. The obtained data are analyzed in the framework of the crystal field theory. The Ni²⁺ ions are located in two crystallographically nonequivalent positions 2a and 4f with point symmetry groups C_2h and C₂, respectively, surrounded by six oxygen ions forming deformed octahedra. The absorption spectra exhibit three intense bands corresponding to spin-resolved transitions from the ground state of nickel ion ³A_2g (³F) to the sublevels of the ³T_2g (³F), ³T_1g (³F) and ³T_1g (³P) triplets split by the spinorbit interaction and the rhombic component of the crystal field. At temperatures below 100 K, the spectra exhibit a thin structure, in which phonon-free lines can be distinguished. Comparison of the calculated frequencies of the zero-phonon transitions with the experimental data allows estimating parameters of the crystal field acting on the nickel ions in the 2a- and 4f-positions, as well as the parameters of electrostatic interaction between the 3d electrons and spin-orbit interaction constants.     

Hyperfine nuclear interaction at copper lattice sites of high-temperature superconductors studied by <Superscript>61</Superscript>Cu(<Superscript>61</Superscript>Ni) Mössbauer emission spectroscopy

Mössbauer emission spectroscopy on the ⁶¹Cu(⁶¹Ni) isotope has been used to determine the quadrupole coupling constant C(Ni) and magnetic induction B(Ni) for the ⁶¹Ni²⁺ probe at copper sites in Cu₂O, CuO, La_{2 ?x}Ba_xCuO₄, Nd_2?xCe_xCuO₄, RBa₂Cu₃O₆, and RBa₂Cu₃O₇ (R=Y, Nd, Gd, Yb). The compounds containing divalent copper were found to exhibit linear C(Ni) vs. C(Cu) and B(Ni) vs. B(Cu) relations [C(Cu) and B(Cu) are the quadrupole coupling constant and magnetic induction for the ⁶³Cu probe, respectively, found by NMR], which is interpreted as an argument for the copper being in divalent state. The deviation of the data points corresponding to the Cu(1) sites in RBa₂Cu₃O₆ and RBa₂Cu₃O₇ from the C(Ni) vs. C(Cu) straight line may be due either to the copper valence being other than 2+ (in the RBa₂Cu₃O₆ compounds) or to the principal axes of the total and valence electric field gradient being differently oriented (in the RBa₂Cu₃O₇ compounds).     

Evolution of the structure and magneto-optical properties of Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>3 − <Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4</Subscript> films prepared by solid-state reactions

This paper reports on the results of investigations into the structure and the magnetic and magnetooptical properties of thin films Mn _x Fe_{3 ? x} O₄ prepared by solid-state reactions: isothermal annealing, self-propagating high-temperature synthesis, and a combination of these two regimes. The regimes favorable for the formation of films close in composition and structure to the stoichiometric compounds MnFe₂O₄ or Fe₃O₄ are established. The features observed in the spectral response of the magneto-optical Faraday effect and of the magnetic circular dichroism of the MnFe₂O₄ films are considered in terms of the electronic transitions in magnetic ions, primarily Fe³⁺, which occupy octahedral positions in the spinel structure.