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The inclusion of charge transfer to the conduction band in a cluster model analysis of some 3d transition metal chalcogenides

A. E. Bocquet, Takashi Mizokawa, Kazutoshi Mamiya, Atsushi Fujimori, Masanori Matoba, Shuichiro Anzai, Shigemasa Suga, and Tomonao Miyadai

Journal of Electron Spectroscopy and Related Phenomena 78 111-114 1996年05月

研究論文（学術雑誌）, 共著, 査読有り

Photoemission Study of Itinerant Ferromagnetic Cr_1-δTe

Kenya Shimada, Tomohiko Saitoh, Hirofumi Namatame, Atsushi Fujimori, Setsuro Ishida, Shoji Asano, Masanori Matoba, and Shuichiro Anzai

Physical Review B 53 7673-7683 1996年03月

研究論文（学術雑誌）, 共著, 査読有り

The electronic structures of the itinerant ferromagnets Cr_1-x_Te (x=0.05, 0.25, and 0.375) have been studied by photoemission spectroscopy. The valence-band spectra are compared with the density of states given by band structure calculations. In spite of the itinerant nature of the d electrons, disagreement between the photoemission spectra and the band-structure calculations exists in the magnitude of the d-band exchange splitting and the spectral weight at the Fermi level and 2–4 eV below it: The occupied d band for x=0.05 is shifted away from the Fermi level; the observed spectral weight at the Fermi level is significantly suppressed compared with the band structure calculations for x=0.05 and 0.375, where the nominal d-electron numbers are close to integers 4 and 3, respectively. Configuration-interaction cluster-model calculations have been made for x=0.05 and 0.375 to explain the spectral weight distribution in the high-binding-energy (2–4 eV) region in terms of electron-correlation effects. The d-d on-site Coulomb energy is estimated to be significant, U=2 eV, and nearly equal to or smaller than the charge-transfer energy Δ=2–3 eV.

Effect of charge transfer to the conduction band within a single-impurity model on tne Ni 2p core level line shapes of Ni compounds

A. E. Bocquet, Takashi Mizokawa, Kazutoshi Mamiya, Atsushi Fujimori, Masanori Matoba, Shuichiro Anzai and Shigemasa Suga

Physical Review B 52 13838-13849 1995年11月

研究論文（学術雑誌）, 共著, 査読有り

We have extended the single-impurity cluster model to include the effects of charge transfer to the conduction band. It is found that these effects can have a considerable influence on the line shapes of core-level spectra of small-gap transition-metal compounds. Using a few additional, well-defined parameters to describe the interactions between the local cluster and the conduction band, and retaining the original intracluster parameters from previous single-impurity models, we find an improved agreement for the Ni 2p spectrum of NiS. The asymmetric line shape is well reproduced, keeping the correct satellite to main peak ratio, which is not possible using the three-peak structure of previous models. The new model is less successful in explaining effects beyond standard single-impurity models in more ionic compounds, such as the double-peak stucture of the main line of the core-level spectrum of NiO, where the interactions between the metal d site and the conduction band are expected to play a lesser role.

Effect of Co Substitution on the Magnetic Properties of the Ni₂In-Type Mn₇Sn₄

Naoya Tokiwa, Tkayuki Yoshida, Toshihiko Shimomura, Ryoichi Sugi, Masanori Matoba, and Shuichiro Anzai

Physica Status Solidi b 189 K33-K36 1995年08月

研究論文（学術雑誌）, 共著, 査読有り

Effect of 4d Transition Metal Rh Doping on Thermoelectric Power, Magnetic Susceptibility, Thermal Expansion and X-ray Photoemission Spectra in the Charge-Transfer Type Nonmetallic State of NiS

Hideya Ikoma, Masanori Matoba, Mitsuo Mikami and Shuichiro Anzai

Journal of the Physical Society of Japan 64 2600-2608 1995年08月

研究論文（学術雑誌）, 共著, 査読有り

We report the following two remarks of the Rh impurity effect on the charge-transfer (CT) type nonmetallic state (below the nonmetal-metal transition temperature: T_t_) of 3d transition metal compound NiS. (1) Although the nearest neighbouring M-M (Ni or Rh) and S-S distances increase with increasing x, dT_t_/dx<0. The Rh substitution gives a broad peak with the Fermi edge. A positive sign of T-linear contribution of the thermoelectric power turns to negative one at the critical concentration (x_c_) in Ni_1-x_Rh_x_S. Below T_t_, a Curie constant is observed and increases with increasing x. It is suggested that an impurity band introduced by the Rh atoms leads a change of the electronic state of Ni atoms and the suppression of the CT gap. (2) An empirical relation (dT_t_/dC_N_ >0) is found on Ni_1-x_Rh_x_S, Ni_1-δ_S and NiS_1-y_Se_y_, where C_N_ is the phonon-drag coefficient. The slope dT_t_/dC_N_ becomes smaller in Ni_1-x_M_x_S with the early 3d transition metal impurities (M: Ti, V and Cr).

Electronic Effect of Mn Addition (y) on the Magnetic Properties of the Ni₂In-Type Mn_7+ySn₄

Ryoichi Sugi, Toshiaki Shimomura, Masanori Matoba, Shingo Matsuzaka, Seiji Fujii, Naoto Hagiwara and Shuichiro Anzai

Physica Status Solidi b 189 K65-K68 1995年08月

研究論文（学術雑誌）, 共著, 査読有り

The inclusion of charge-transfer to the conduction band in a cluster model analysis of core level line shapes

A. E. Bocquet, Takashi Mizokawa, Kazutoshi Mamiya, Atsushi Fujimori, Masanori Matoba, Shuichiro Anzai and Shigemasa Suga

Journal of Physics, Condensed Matter 7 L411-L416 1995年05月

研究論文（学術雑誌）, 共著, 査読有り

We have extended the single-impurity cluster model to include the effects of charge transfer to the conduction band for the interpretation of the core level photoemission spectra of highly correlated, small-gap semiconducting and metallic transition metal compounds. The model includes the charge fluctuations between the local transition metal site and the conduction band and has been successfully applied to reinterpret the spectra of some 3d transition metal chalcogenides, reproducing well the large asymmetry of the main peaks, as well as the other satellite structures.

Opening of a Correlation-Induced Band Gap in NiS

Motohiko Nakamura, Akira Sekiyama, Hirofumi Namatame, Atsushi Fujimori, Akira Misu, Hideya Ikoma, Masanori Matoba and Shuichiro Anzai

Physical Review Letters 73 2891-2894 1994年11月

研究論文（学術雑誌）, 共著, 査読有り

We have measured high-resolution photoemission spectra of NiS, which undergoes a nonmetal-metal transition at Tt~260 K. Below Tt, a small band gap opens; the band edge is essentially a step function broadened only by ~ 15 meV. This observation is difficult to reconcile with one-electron band theory, which predicts a much broader band edge, implying a dramatic influence of electron correlation on quasiparticle excitations and on the opening of a band gap in 3D antiferromagnetic insulators.

半導体Cu₄(Sn_1-xGe_x)S₄の熱電能

杉野哲也, 田口直文, 的場正憲, 安西修一郎

日本材料科学会誌 31 130-132 1994年09月

研究論文（学術雑誌）, 共著, 査読有り

Effect of Early Transition-Metal (M=Ti, V and Cr) Doping on the Electronic Structure of Charge-Transfer Type Compound NiS Studied by Thermoelectric Power and X-Ray Photoemission Measurements

Masanori Matoba, Shuichiro Anzai and Atsushi Fujimori

Journal of the Physical Society of Japan 63 1429-1440 1994年07月

研究論文（学術雑誌）, 共著, 査読有り

The M 2p core-level XPS peaks of doped elements in Ni1-xMxS are observed at the binding energies of M in “M2S3” rather than those of “MS” below and above the nonmetal-metal transition temperature (T t), indicating that the M atom are ionized to M3+ and acts as shallow donor impuritites. Below T t the T1/2 contribution with negative sign to the thermoelectric power (S) is superimposed on the usual degenerate semiconductive contribution with positive sign. It overcomes the latter contribution above a concentration (x c). The value of x c increases in the order of M=Ti, V and Cr. These results indicate that the T1/2 contribution to S comes from variable range hopping through the localized states formed near E F within the narrow charge-transfer gap of the parent NiS. Above T t the sign of S is negative in the electron-doped Ni1-xMxS as well as in the hole-doped Ni1-xS, suggesting that they have the Fermi surface topology.

強相関電子系NiSの電子構造と磁気的電気的性質：不純物ドーピングによる物性制御要因の探求

的場正憲

平成６年度東北大学金属材料研究所報告 83-105 1994年

研究論文（その他学術会議資料等）, 単著

Pressure Effect on the Magnetic Transition Temperatures of Mn₇Sn₃Ge and Mn₇Sn₂Ge₂

Satoru Ohta, Naoto Hagiwara, Seiji Fujii, Hajime Yoshida, Takejiro Kaneko, Shuichiro Anzai and Masanori Matoba

Japanese Journal of Applied Physics 32-3 266-268 1994年

研究論文（学術雑誌）, 共著, 査読有り

Magnetic Properties of Cr₂RhSe₄ and CrRh₂Se₄

Shuichiro Anzai, Masaaki Ohji, Satoru Ohta, Tetsuya Matsukami, Kiyoshi Sonokawa and Masanori Matoba

Japanese Journal of Applied Physics 32-3 311-312 1994年

研究論文（学術雑誌）, 共著, 最終著者, 査読有り

X-Ray Absorption Study of the Metal-Nonmetal transition in NiS and Ni_1-xM_xS (M=Fe and Co)

Motohiko Nakamura, Hirofumi Namatame, Atsushi Fujimori, Maurizio Sacchi, John C. Fuggle, Akira Misu, Takeshi Mamori, Hikaru Tamura, Masanori Matoba, and Shuichiro Anzai

Japanese Journal of Applied Physics 32-3 306-307 1994年

研究論文（学術雑誌）, 共著, 査読有り

Photoemission Study of the Electronic Structure of the Ferromagnetic Cr_1-δTe System

Kenya Shimada, Tomohiko Saitoh, Hirofumi Namatame, Atsushi Fujimori, Masanori Matoba, Kazuo Hatakeyama and Shuichiro Anzai

Japanese Journal of Applied Physics 32-3 355-356 1994年

研究論文（学術雑誌）, 共著, 査読有り

Metal-nonmetal transition in NiS induced by Fe and Co substitution: X-ray absorption spectroscopic study

Motohiko Nakamura, Atsushi Fujimori, Maurizio Sacchi, John C. Fuggle, Akira Misu, Takeshi Mamori, Hikaru Tamura, Masanori Matoba and Shuichiro Anzai

Physical Review B 48 16942-16947 1993年12月

研究論文（学術雑誌）, 共著, 査読有り

In order to reveal the microscopic origin of the metal-nonmetal transition in NiS, we have studied the Ni 2p x-ray-absorption spectra of substituted systems Ni_1-x_M_x_S (M=Fe,Co), whose transition temperature T_t_ varies from 500 K (Ni_0.5_Fe_0.5_S) to below 4 K (Ni_0.94_Co_0.06_S). Spectra taken at room temperature have been analyzed using a configuration-interaction cluster model to deduce changes in the electronic structure parameters, namely, the S-3p-to-Ni-3d charge-transfer energy Δ and the Ni3d –S3p transfer integral T. We find that Fe substitution does not increase the local Ni-S distance as would be expected from the lattice parameters but affects energy levels as is reflected in Δ. The changes in Δ and T derived from the cluster-model analysis explain the increase in the charge-transfer-type band gap in Ni_1-x_Fe_x_S and hence the increase in T_t_ within the cluster model, whereas they do not explain the decrease in T_t_ in Ni_1-x_Co_x_S. In order to explain the dramatic decrease in T_t_ with Co substitution, we propose that the Ni3d–Co3d hybridization increases the bandwidths leading to the closure of the band gap.

X-Ray Absorption Study of the Metal-Nonmetal transition in NiS and Ni_1-xCo_xS

Motohiko Nakamura, Hirofumi Namatame, Atsushi Fujimori, Maurizio Sacchi, John C. Fuggle, Akira Misu, Takeshi Mamori, Hikaru Tamura, Masanori Matoba and Shuichiro Anzai

Photon Factory Activity Report 11 26 1993年

研究論文（その他学術会議資料等）, 共著

Effect of Ge Substitution on the Magnetic Transition Temperature in the Ni₂In-Type Mn₇(Sn_1-xGe_x)₄

Shuichiro Anzai, Naoto Hagiwara, Seiji Fujii, Shinji Kameyama, Masanori Matoba, Takejiro Kaneko, Hajime Yoshida and Satoru Ohta

Physica Status Solidi b 177 K13-K16 1993年

研究論文（学術雑誌）, 共著, 査読有り

A Spin-Glass-Like State in the Ni₂In-Type Mn₇(Sn_1-xGe_x)₄ below the Ferrimagnetic State

Naoto Hagiwara, Masanori Matoba, Seiji Fujii and Shuichiro Anzai

Physica Status Solidi b 176 K71-K74 1993年

研究論文（学術雑誌）, 共著, 査読有り

X-Ray Photoemission Spectroscopy Study of Impurity Effect and d-Band Formation Induced by the Substituted 4d Transition Metal Atoms in Ni_1-xRh_xS

Takeshi Mamori, Masanori Matoba, Shuichiro Anzai and Atsushi Fujimori

Journal of the Physical Society of Japan 62 1031-1036 1993年

研究論文（学術雑誌）, 共著, 査読有り

The effect of Rh substitution on the electronic structure of charge transfer type compound NiS is studied by XPS. We find the following results. (1) A narrow band is newly superimposed on the main peak (d^8^L) of NiS in the valence band region and its width increases with x. (2) The peak position and the line shape of Rh 3d core level spectra are very close to that of Rh metal. (3) The S 2s and the S 2p_3/2_ core level peaks shift toward higher binding energy (E_B_) with increasing x. (4) The Ni 2p_3/2_ core level main peak (d^9^L) shifts toward lower E_B_ with increasing x. (5) The E_B_ separation of the Ni 2p_3/2_ main and satellite peaks decreases as x increases, while the relative intensity of the latter peak to the former one increases. We suggest a tentative model that a Mott-Hubbard type metallic d-band is superimposed on charge transfer type host NiS, and that this contribution is one of the electronic origin for dT_t_/dx<0 reported previously. The origin of the metallic band is attributed to the Rh-Rh and/or Ni-Rh interactions in Ni_1-x_Rh_x_S.

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