Papers by Author: Kosuke Suzuki

Abstract: We developed the photon counting CT system by using a conventional laboratory X-ray source and a CdTe line sensor. Attenuation coefficients were obtained from the measured CT image data. Our suggested method for deriving the electron density and effective atomic number from the measured attenuation coefficients was tested experimentally. The accuracy of the electron densities and effective atomic numbers are about <5 % (the averages of absolute values are 2.6 % and 3.1 %, respectively) for material of 6< Z and Zeff <13. Our suggested simple method, in which we do not need the exact source X-ray spectrum and detector response function, achieves comparable accuracy to the previous reports.

Abstract: We have proposed a method to obtain the electron density and effective atomic number from the attenuation coefficients of multi-energy X-rays. The simulations were performed using NIST’s database and demonstrate that our approach can facilitate electron density measurements within accuracy of 1% in a human body. The proposed method exhibited an improvement in the accuracy of electron density measurements, which were obtained from experimental linear attenuation coefficients using a conventional laboratory X-ray source with energy spectrum.

Abstract: In this study, we calculate electronic structures for Mn₂O₄ and LiMn₂O₄ by using CRYSTAL14 ab-initio calculation code in order to understand electrode reaction mechanism of Li_xMn₂O₄ by lithiation/delithiation. Mulliken population analysis for all electrons show that the redox orbitals with lithiation and delithiation is O 2p orbitals. However, difference charge densities between majority and minority electrons indicate the change of distribution in Mn 3d orbitals by lithiation. This modification of distribution in Mn 3d orbitals suggests the change of electron configuration because the number of electrons at Mn atom is almost constant in Mulliken population analysis for all electrons. As a result, this modification of distribution in Mn 3d orbitals improves electron conductivity of this material.

Abstract: The purpose of this research is to reduce the measurement time of the first-order mass moment estimation method proposed by us previously. In the previous method, the loads at the three points of the board are measured one by one using one piece of an expensive scale (model: GX-30KR, resolution: 0.1 g, price: 2,542 USD). The relative standard uncertainly of measurement using a rigid body is estimated to be 1.7% and the measurement time is approximately 10 minutes. In this research, three pieces of inexpensive scales (model: HD-660, resolution: 100 g, price: 17 USD) are used to reduce the measurement time. The relative standard uncertainly of measurement is estimated to be 1.9% and the measurement time is approximately 1 minute. In previous measurement, when changing the position of the scale, the position of the frame has been deviated slightly. However, in this method, this kind of error does not occur, since measurements of three points are simultaneously conducted.

Abstract: Co/Pd magnetic multilayers have been prepared by using a sputtering method. Lattice distances and magnetic hysteresis curves have been measured by X-ray diffraction (XRD) measurements and magnetization measurements using a vibrating sample magnetometer (VSM). The XRD measurements have shown that the samples with thinner Pd layers have shorter lattice distances, and the VSM measurements have shown that the samples of thinner Co and thicker Pd layers are closer to those of perpendicular magnetic anisotropy. We have applied the X-ray magnetic diffraction method to the Co/Pd multilayer for the first time and have succeeded in observing a change in the X-ray diffraction intensities by the reversal of the magnetization direction.

Abstract: We have applied two kinds of experimental methods using elliptically polarized synchrotron X-rays, magnetic Compton and Bragg scattering experiments, to a single crystal of a disordered Pd_0.80Co_0.20 alloy, and have measured magnetic Compton profiles and magnetic form factors, respectively. The result of the Compton scattering experiment has shown that the electronic structure of Pd_0.80Co_0.20 is similar to that of Pd_0.72Co_0.28, and the spin moment has been evaluated. The result of the Bragg scattering experiment has reinforced that of the previous experiment [M. Ito et al.: Mater. Sci. Forum Vol. 459 (2011), p. 3.], and the spin moment estimated by the magnetic Bragg scattering has reproduced that by the magnetic Compton scattering. These results show that the joint study of the magnetic Compton and Bragg scattering provides a tool for investigating the magnetic property of alloys.

Abstract: Magnetic Compton profiles (MCPs) of Co/Au multilayers have been measured and analyzed by DV-Xα cluster model calculations from a viewpoint of perpendicular magnetic anisotropy (PMA). The PMA and the MCPs are discussed for the presently obtained results for Co/Au, along with the previously obtained results for Co/Pd and Co/Pt. A Co/Au multilayer shows a weak PMA which is caused by |m|=1 states of Co 3d electrons at a smooth Co/Au interface. The increase of the interface-to-volume ratio plays the main role in determining the perpendicular anisotropy in Co/Au multilayers. The strain of a Co layer can have a secondary role in determining the magnetic anisotropy in Co/Au multilayers, although the strain dominates PMA in the case of Co/Pd and Co/Pt multilayers.

Abstract: We have measured magnetic Compton scattering (MCS) for an Fe/MgO multilayer film at several magnetic field applying perpendicular to film plane. A spin specific magnetic hysteresis (SSMH) loop is obtained by the MCS for the Fe/MgO multilayer film. A knickpoint is observed in the SSMH loop around the magnetic field of 0.5 T. Orbital magnetization is enhanced within the magnetic field from-0.5 T to 0.5 T. A decomposition analysis for magnetic Compton profiles shows the suppressed |m|=0 states and enhanced |m|=1 and 2 states within the magnetic field from-0.5 T to 0.5 T. Here m denotes magnetic quantum number. The knickpoint corresponds to a perpendicular magnetic anisotropy, which comes from the enhanced |m|=1 and 2 state and orbital magnetization in the Fe/MgO multilayer.

Abstract: sotropic and directional autocorrelation functions have been calculated using the DV-Xα method on polyethylene type clusters to investigate the effect of its characteristic dimensionality of the wavefunctions. Directional autocorrelation functions are calculated along the c-axis, the direction of the long chain of carbon atoms, and along an axis perpendicular to it. The analysis of the molecular orbital dependence of the autocorrelation function reveals that the long range order along the c-axis can be enhanced as increasing the length of the cluster and the orbitals near the highest occupied molecular orbital have a key role for the one-dimensional order.

Abstract: sotropic and directional autocorrelation functions are calculated for 14 electron diatomic molecules, N₂, CO, and BF, using the DV-Xα method. In order to investigate the effect of chemical bonds for the molecules, directional autocorrelation functions parallel and perpendicular to the bond are investigated. The anisotropies of the directional autocorrelation functions of N₂ and CO are different from the anisotropy of BF, which has a wave shape.