Toshiaki Iwazumi

An x‐ray spectrometer for Compton scattering

An x‐ray spectrometer has been designed and constructed for Compton scattering measurements using 40–70 keV x‐rays from an ellipsoid multipole wiggler (EMPW) installed in the accumulation ring of the National Laboratory for High Energy Physics at Tsukuba. The spectrometer has four sets of a Cauchois‐type energy analyzer and an imaging plate, which are arranged on the surface of a cone and share a scattering angle of 160°. In each energy‐analyzing system, to increase signal to noise ratio a set of vertical and horizontal slits are inserted between the analyzer and the imaging plate. A resolution of 0.13 a.u. in terms of electron momentum was achieved. A Compton profile of a vanadium single crystal was measured with an integrated counting rate of 400 counts/s.

The Dependence of the Superconducting Transition upon the Quench Temperature of YBa2Cu3Oy

The superconducting transition properties have been evaluated for YBa2Cu3Oy compound samples prepared after processing from vairous quench temperatures following a sintering stage at 880°C. Two sets of temperatures depicting the onset of the superconducting transition have been observed. One set is found to cover 79-94 K for samples with orthorhombic symmetry, and the onset temperature increases as the quench temperature is lowered. The other set is found to cover the range 52-58 K for samples with tetragonal symmetry.

Study on copper valency of high-tc superconductor YBa2Cu3O7−y by high temperature X-ray absorption spectroscopy

Abstract The X-ray absorption spectra of the Cu K-edge have been obtained for a high-T c superconductor YBa 2 Cu 3 O 7−y by in-situ high temperature measurements between room temperature and 600 °C and for quenched samples prepared by rapid cooling from various temperatures up to 880 °C. The results indicate that the copper valency is predominantly 2+ and the monovalent state appears as the oxygen contents decrease with increasing temperature. The Cu K-edge X-ray absorption spectra of lanthanoide compounds with oxygen-deficient triperovskite structure, LnBa 2 Cu 3 O 7−y (Ln=Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, or Lu) were also reported.

Thermal phase transition of RbMnFe(CN)6 observed by X-ray emission and absorption spectroscopy

The thermal phase transition of RbMnFe(CN)6 has been observed by Mn and Fe 3p–1s X-ray emission spectroscopy (XES) and 1s X-ray absorption spectroscopy (XAS). The thermal variations of the spin states and the valences of Mn and Fe were determined to be Mn2+(S=5/2)–NC–Fe3+(S=1/2) for the high-temperature (HT) phase and Mn3+(S=2)–NC–Fe2+(S=0) for the low-temperature (LT) phase. These transitions are thus caused by charge transfer between Mn and Fe. The temperature dependences of Mn and Fe 3p–1s XES and 1s XAS were observed as the composition of the spectra of the HT and LT phases. The ratios of the HT component in each spectrum show good agreement with the thermal transition curves observed with magnetic susceptibility measurements.

Improvement of a sagittally focusing double-crystal monochromator

Establishment of the parallelism between two axes, that of x rays and that of the cylinder made by a bent crystal, is found to be important when a sagittally focusing double‐crystal monochromator is used. Detectable increase of reflection width and decrease of output intensity is observed when the angle between the above two axes becomes only 0.1°. With the help of rotation stages to adjust the axis of the cylinder, the focus smaller than 1 mm is obtained up to 11 keV at BL‐6B of the Photon Factory and about 3 mm is established up to 28 keV at NE1 of the Accumulation Ring.

Magnetic XANES of circularly polarized X-ray absorption on Fe and Ni metals and Nd2Fe14B compound

Magnetic effects in the X-ray absorption process have been measured using circularly polarized X-rays emitted from an elliptical multipole wiggler. Magnetic XANES spectra on the K -edge of Fe and Ni taken by the transmission method show positive and negative spin polarizations, respectively, near the Fermi level which are consistent with the results in literature. A large positive magnetic XANES spectrum on the Nd L 2 -edge of Nd 2 Fe 14 B compound measured by the fluorescent method indicates that the unoccupied 5 d -bands are polarized due to a significant hybridization between 4 f - and 5 d -states. The magnetic XANES spectrum on the Nd L 3 -edge has a structure below the Fermi level, suggesting a quadrupole transition contribution of the partially vacant majority band of 4 f -states.

Superconductivity and Crystal Structure of LaBa2Cu3-xOy Compounds

An extensive study of magnetic, electrical transport, and structural properties of the normal and superconducting states of LaBaCuO2BO3 are presented. A ceramic compound of LaBaCuO2BO3 has been synthesized by the solid-state reaction technique under ambient pressure by reacting BaCO3, La2O3, CuO and B2O3. LaBaCuO2BO3 compound was characterized by x-ray diffraction and scanning electron microscope-x-ray energy dispersion spectrum analyses. Rietveld refinement of powder x-ray diffraction data indicated that the compound is P4bm space group symmetry and a=5.57475(8), c=7.5056(l)A. Measured magnetic susceptibilities of powder specimens of LaBaCuO2BO3 compound indicate a transition to a diamagnetic state at 32 K.

Preparation and Property of La1.85Sr0.15CuO4 Single Crystal

A single crystal of the high Tc superconductor, La1.85Sr0.15CuO4, was prepared using the solid phase reaction, and the magnetization was investigated. In the superconducting state, strong anisotropic diamagnetism was observed for external magnetic field parallel and perpendicular to the c-axis. This result supports the two-dimensional character of Sr-La-Cu-O system.

New beamline (BL‐28B) for circularly polarized x rays at the Photon Factory

Design and experience of the initial operation of a new beamline (BL‐28B) for an elliptical‐multipole wiggler constructed at the Photon Factory are described. An indirect‐water‐cooled premirror has been installed for horizontal focusing and vertical collimating. The fixed‐exit double‐crystal monochromator also has an indirect‐water‐cooled system. The post‐mirror has been commissioned in order to refocus the x‐ray beam vertically and cut the higher harmonics of the monochromatized x rays. All the elements of this beam line are high‐vacuum compatible.

Magnetic Circular Dichroism of Resonant X-Ray Emission Spectroscopy in the Transverse Geometry

We perform theoretical calculations and experimental measurements for magnetic circular dichroism in resonant X-ray emission spectroscopy (MCD-RXES) in Gd 3+ systems. A general expression of MCD-RXES is obtained theoretically for arbitrary directions of incident and emitted X-rays with an atomic model. It is shown that when the incident X-ray is perpendicular to the magnetization of the sample the MCD-RXES originates from the quantum mechanical interference between the excitation and decay processes. The behavior of MCD-RXES calculated for the 2 p →5 d excitation and 3 d →2 p radiative decay in Gd 3+ is in good agreement with that measured experimentally for a Gd 33 Co 67 amorphous alloy.