Hironobu Shoji

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.

Magnetic Circular Dichroism of Resonant X-Ray Emission Spectroscopy in Longitudinal and Transverse Geometries

Theoretical calculations and experimental measurements are performed for magnetic circular dichroism in resonant X-ray emission spectroscopy (MCD-RXES) in Gd 3+ systems. It is shown that when the i...

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.

Resonant X-Ray Emission Spectra by the Electric Quadrupole Excitation at the Mn K-Edge of MnO

We study the incident, the scattering and the azimuthal angle dependences of the Mn K β resonant x-ray emission spectroscopy (RXES) due to the electric quadrupole excitation by tuning the incident photon energy to the pre-edge region of the Mn K -edge for a MnO single crystal both experimentally and theoretically. RXES caused by the electric quadrupole excitation shows a strong sensitivity to these angles, and the agreement between theory and experiment is good. Different angle dependences are shown between the excitation to the T 2 g orbital and that to the E g one. It is discussed that RXES can be a powerful tool to separate the electric quadrupole and dipole contributions in the pre-edge region of the transition-metal K -edge in transition metal compounds.

Resonant Inelastic X-Ray Scattering at the K Edge of Ge

We study the resonant inelastic x-ray scattering (RIXS) at the K edge of Ge. We measure RIXS spectra with systematically varying momenta in the final state. The spectra are a measure of exciting an electron–hole pair. We find a single-peak structure (except the elastic peak) as a function of photon energy, which is nearly independent of final-state momenta. We analyze the experimental data by means of the band structure calculation. The calculation reproduces well the experimental shape, clarifying the implication of the spectral shape.

Magnetic circular dichroism of Gd 3d–2p and 4d–2p X-ray emission in ferrimagnetic Gd–Co amorphous

Abstract The magnetic circular dichroism (MCD) of the Gd X-ray emission spectra (XES) in the 3d–2p and 4d–2p radiative transitions of ferrimagnetic Gd–Co amorphous were observed when the incident X-ray energies were exactly on and sufficiently higher than the Gd L 3 and L 2 absorption edges. The obtained results at the high-energy off-resonance correspond well with a recent theoretical analysis based on an atomic calculation with the full multiplet included. The magnifying feature of the magnetic-resonance effects of the MCD–XES at the on-resonance is consistent with the results of the MCD of the X-ray absorption spectrum.

Spin-State Transitions in an Iron Spin-Crossover Complex Observed with X-ray Emission and X-ray Absorption

The thermal- and photon-induced phase transitions of [Fe(2-pic) 3 ]Cl 2 EtOH from a high-spin (HS) state ( S = 2) to a low-spin (LS) state ( S = 0) were observed by X-ray Emission Spectroscopy (XES) and X-ray Absorption Spectroscopy (XAS). The spin state was observed with Fe 3p-1s XES from the HS and photon-induced (PI) phase took S = 2 and LS state took S = 0. Each spectrum of the decay process from the PI phase to the LS state could be described with the superposition of those of the HS and LS states. In XAS, a different spectrum was also observed in the HS and LS states, and likewise by XES; the difference in the pre-edge structure between the HS and LS states was explained based on the difference of Fe unoccupied 3d partial density of state calculated by the DV-X f method.

Resonant fluorescence emission of Mn Kβ in quasicrystals

Abstract Resonant X-ray emission spectra of Mn Kβ 1,3 (3p ⋅ 1s) were measured near the Mn K absorption edge for quasicrystalline icosahedral Al–Pd–Mn, icosahedral Al–Pd–Mn–B, icosahedral Al–Mn–Si, decagonal Al–Mn–Fe–Ge and crystalline α–Al–Mn–Si. Except for the Raman scattering energy region, the peak energy of Kβ 1,3 is independent of incident photon energy for all the samples. The shape was also unchanged. A Kβ’ subpeak, which is caused by the splitting between the density of states of the high spin and the low spin in the 3p band, appeared in all the quasicrystal samples with lower intensity than those of the Mn oxides in spite of the fact that Mn atoms in the decagonal Al–Mn–Fe–Ge and the icosahedral Al–Pd–Mn–B are in a ferromagnetic state. In the profile of the icosahedral Al–Pd–Mn, α–Al–Mn–Si and decagonal Al–Mn–Fe–Ge, a clear hump was observed at the energy between Kβ 1,3 and Kβ’. In the emission spectra of Mn Kβ 5 (3d →1s), peak positions were 1.5 eV lower for the ferromagnetic quasicrystals than those of the other quasicrystals.

Magnetic circular dichroism of 3d5/2 2p3/2 resonant inelastic X-ray scattering at the Ho LIII-edge in Ho3Fe5O12

Magnetic circular dichroism (MCD) of resonant inelastic X-ray scattering (RIXS) of 3d5/2 2p3/2 decay (Ho L1) was measured at the Ho LIII-edge in Ho3Fe5O12. The MCD-RIXS, in which the intermediate state has the 2p 4fn + 1 configuration due to the quadrupolar transition of 2p 4f, was also observed at the pre-edge region of the Ho LIII-edge. The obvious superposition of two peaks, which comes from the high-energy off-resonant Raman scattering and the fluorescence, could be found in both the RIXS and the MCD-RIXS when the energy of the incoming X-ray was 7eV higher than the white line. The dependence of the integration of the MCD-RIXS spectra on the incident x-ray energy could roughly reproduce the MCD of X-ray absorption spectra (XAS).

X-ray magnetic circular dichroism in quasicrystals

Abstract The spectra of X-ray magnetic circular dichroism (XMCD) and extended X-ray absorption fine structure (EXAFS) were measured in the ferromagnetic quasicrystals (a stable decagonal phase of Al 40 Mn 25 Fe 15 Ge 20 , a unstrained icosahedral phase of Al 50 Pd 15 Mn 20 B 15 , a strained icosahedral phase of Al 42.5 Pd 7.5 Mn 30 B 20 ) and the orthorhombic approximant crystalline phase of Al 30 Mn 40 B 30 . In Al 40 Mn 25 Fe 15 Ge 20 , the intensity of XMCD at Mn K-edge and Fe K-edge were −7×10 −5 and −5×10 −5 , respectively, which are normalized by the edge jump of the normal absorption spectra. The values suggest that Mn and Fe in this alloy contribute to the magnetism to the same degree. From the result of EXAFS, the nearest neighbors of Mn atoms and Fe atoms were analyzed to be at the same distance. The environment around Mn and Fe were found not so similar except for the nearest neighbor distance. In Al 50 Pd 15 Mn 20 B 15 , Al 42.5 Pd 7.5 Mn 30 B 20 and Al 30 Mn 40 B 30 alloys, the intensity of XMCD around the Mn K-edge were about −3×10 −4 . The magnetic moments of Mn atoms in these alloys are roughly estimated to be 0.8μ B . The difference of a magnetic structure was detected between the quasicrystals and the approximant. The result of EXAFS analysis indicates that the distances from Mn to its first nearest neighbor and its second nearest neighbor are almost equal. The existence of phason strain field have no appreciable influence on the moment of Mn.