Kazutoshi Mamiya

Electronic structure of 3d transition metal pyrites (M = Fe, Co or Ni) by analysis of the M 2p core-level photoemission spectra

We have reinterpreted the metal 2p core-level x-ray photoemission spectra of the 3d transition-metal pyrites , and using a new version of the single-impurity cluster model which includes the effects of charge transfer to the conduction band. By accounting for the effective screening of the strong core-hole potential involving the unfilled S 3p orbitals on the ligand sites, we can successfully model the highly asymmetric lineshapes and weak satellite structures found for and . Reduced screening in leads to the appearance of strong satellite structures and the spectrum is best interpreted using the screening channel to the narrow upper Hubbard band. These results indicate the importance of the empty ligand orbitals when interpreting the physical properties of the pyrite-type chalcogenides.

Soft X-ray Magnetic Circular Dichroism Study of Uranium Monochalcogenides at Uranium N4,5 Absorption Edges

X-ray magnetic circular dichroism (XMCD) was measured for the ferromagnetic uranium monochalcogenides US and USe at U N 4,5 absorption edges in the soft X-ray region. The obtained N 4,5 XMCD signal of US was comparable to the M 4,5 XMCD signal obtained in previous studies. From the sum-rule analysis of XMCD data, it was shown that the estimated ratios of orbital magnetic moment to spin magnetic moment |µ L /µ S | were almost the same for US and USe. The analysis of the XAS branching ratio indicated an increase in 5 f electron occupation number from US to USe, which may suppress the increase in |µ L /µ S |.

Fe Chalcogenides by X-ray Photoemission Spectroscopy

In this article, x-ray photoelectron spectroscopy (XPS) spectra of iron chalcogenides, FeS, Fe7S8, and Fe7Se8 are presented. FeS (troilite) and Fe7S8 (pyrrhotite) are among the most common iron compounds on earth. FeS is antiferromagnetic below the Neel temperature of TN=593–598 K. Above Tα=420 K, FeS is a metal with an NiAs-type crystal structure, but becomes an insulator with a narrow band gap of 0.04 eV below Tα. This transition known as the α-transition is accompanied by a small displacement of the Fe and S atoms from the regular NiAs-type structure. Fe7S8 and Fe7Se8 are ferrimagnetic metals with Neel temperatures of TN=578 and 423–460 K, respectively. The crystal structures of Fe7S8 and Fe7Se8 are derived from the NiAs-type one by introducing ordered Fe vacancies. The polycrystalline samples were synthesized by the Bridgman method. Clean surfaces were obtained by scraping in situ with a diamond file. All the XPS spectra of the iron chalcogenides are taken at room temperature.

Spin-polarized and spin-integrated photoemission study of itinerant ferrimagnetic iron chalcogenides

Itinerant ferrimagnetic metals Fe7S8 and Fe7Se8 and antiferromagnetic semiconductor FeS have been studied by spin-polarized and spin-integrated photoemission and inverse-photoemission spectroscopy. Comparison with the density of states given by band-structure calculations indicates that the Fe 3d band is narrowed with spectral weight transfer towards higher binding energies and that the intensity at the Fermi level is suppressed. The band narrowing and the spectral weight transfer is reproduced by including the self-energy correction, suggesting the importance of electron correlation. Spin-polarized photoemission spectra of Fe7S8 and Fe7Se8 show negative spin-polarization near the Fermi level and spin-dependent correlation effect.

Temperature-Dependent High-Resolution Photoemission Study of Y1-xCaxTiO3

Temperature-dependent high-resolution photoemission spectroscopy has been performed on Y1-xCaxTiO3 (x=0.37, 0.39, 0.41) single crystals. Electrons in Ti 3d bands are strongly correlated and clear metal-insulator transition is observed in the photoemission spectra for x=0.39. The spectral shapes of O 2p and Ti 2p states are temperature dependent indicating strong coupling between electronic states and lattice distortion.

Soft X-ray Absorption Magnetic Circular Dichroism Study of Ferromagnetic Superconductor UGe2

X-ray absorption magnetic circular dichroism (XMCD) at the U N 4,5 edges was measured for the ferromagnetic superconductor UGe 2 in the normal state. The orbital and spin magneic moments deduced fr...

RESONANCE AND HIGH-RESOLUTION PHOTOEMISSION STUDY OF COS2

Abstract Resonance photoemission spectra have been measured at room temperature for CoS 2 in the Co 2p core absorption region. High-resolution valence-band spectra in the Co 3p absorption region have also been taken at temperatures across the magnetic transition ( T c = 120 K), indicating a slight but remarkable spectral change between the paramagnetic and ferromagnetic phases.

Photoemission study of pyrite-type transition-metal chalcogenides MS2−xSex (MFe, Co, Ni)☆

The electronic structures of pyrite-type transition-metal chalcogenides MS2-xSex (M = Fe, Co, Ni) has been investigated by photoemission and inverse-photoemission spectroscopy. The valence-band spectrum of ferromagnetic CoS2 does not show exchange splitting of the Co 3d peak, in disagreement with band-structure calculations. High-resolution photoemission spectra of NiS1.55Se0.45 shows spectral weight transfer from low (similar or equal to 50 meV) to high (0.2-0.5 eV) binding energies, in going from the metallic to the insulating phase.

Spectral weight transfer and mass renormalization in LnNi2B2C (Ln = Y, La)

Abstract We have studied the electronic structure of rare-earth Ni boro-carbides by high-resolution photoemission. The spectra of superconducting YNi 2 B 2 C and non-superconducting LaNi 2 B 2 C are remarkably similar in spite of large differences predicted by band-structure calculations. The disappearance of the peak in the density of states at the Fermi level is attributed to spectral weight transfer towards higher energies concomitant with the conduction-band mass renormalization.

PHOTOEMISSION AND INVERSE-PHOTOEMISSION STUDY OF FERROMAGNETIC VALENCE FLUCTUATING SYSTEM CEFE2

Abstract Various electron-spectroscopic results including core-level X-ray photoemission, X-ray absorption, Ce 3d-4f and 4d-4f resonant photoemission, and inverse-photoemission spectroscopy on the valence fluctuating ferromagnet CeFe 2 are presented and analyzed with model calculations using the Anderson-impurity Hamiltonian. Surface effects on the spectra are taken into account in the analysis. The valence-band spectra are also compared with the band-structure density of states calculated using the local-spin-density approximation. The validity of describing the Ce 4f states as a localized impurity level and in the 4f band picture is discussed.