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論文

Thickness-dependent magnetic properties and strain-induced orbital magnetic moment in SrRuO$$_{3}$$ thin films

石上 啓介*; 吉松 公平*; 豊田 大介*; 滝沢 優*; 吉田 鉄平*; 芝田 悟朗*; 原野 貴幸*; 高橋 文雄*; 門野 利治*; Verma, V. K.*; et al.

Physical Review B, 92(6), p.064402_1 - 064402_5, 2015/08

https://doi.org/10.1103/PhysRevB.92.064402
 被引用回数：45 パーセンタイル：84.02(Materials Science, Multidisciplinary)

Thin films of the ferromagnetic metal SrRuO$$_{2}$$ (SRO) show a varying easy magnetization axis depending on the epitaxial strain, and undergo a metal-to-insulator transition with decreasing film thickness. We have investigated the magnetic properties of SRO thin films with varying thicknesses fabricated on SrTiO$$_{3}$$(001) substrates by soft X-ray magnetic circular dichroism at the Ru M2,3 edge. Results have shown that, with decreasing film thickness, the film changes from ferromagnetic to nonmagnetic at around 3 monolayer thickness, consistent with previous magnetization and magneto-optical Kerr effect measurements. The orbital magnetic moment perpendicular to the film was found to be 0.1$$mu$$B/Ru, and remained nearly unchanged with decreasing film thickness while the spin magnetic moment decreases. A mechanism for the formation of the orbital magnetic moment is discussed based on the electronic structure of the compressively strained SRO film.

論文

Hybridization between the conduction band and 3$$d$$ orbitals in the oxide-based diluted magnetic semiconductor In$$_{2-x}$$V$$_x$$O$$_3$$

小林 正起*; 石田 行章*; Hwang, J. I.*; Song, G. S.*; 滝沢 優*; 藤森 淳; 竹田 幸治; 大河内 拓雄*; 岡根 哲夫; 斎藤 祐児; et al.

Physical Review B, 79(20), p.205203_1 - 205203_5, 2009/05

https://doi.org/10.1103/PhysRevB.79.205203
 被引用回数：7 パーセンタイル：33.2(Materials Science, Multidisciplinary)

The electronic structure of In$$_{2-x}$$V$$_x$$O$$_3$$ ($$x=0.08$$) has been investigated by photoemission spectroscopy and X-ray absorption spectroscopy (XAS). The V $$2p$$ core-level photoemission and XAS spectra revealed that the V ion is in the trivalent state, which is the same valence state as that of In in In$$_2$$O$$_3$$. The V $$3d$$ partial density of states obtained by the resonant photoemission technique showed a sharp peak above the O $$2p$$ band. While the O $$1s$$ XAS spectrum of In$$_{2-x}$$V$$_x$$O$$_3$$ was similar to that of In$$_2$$O$$_3$$, there were differences in the In $$3p$$ and $$3d$$ XAS spectra between the V-doped and pure In$$_2$$O$$_3$$. The observations give clear evidence for hybridization between the In-derived conduction band and the V $$3d$$ orbitals in In$$_{2-x}$$V$$_x$$O$$_3$$.

論文

Systematic changes of the electronic structure of the diluted ferromagnetic oxide Li-doped Ni$$_{1-x}$$Fe$$_x$$O with hole doping

小林 正起*; Hwang, J. I.*; Song, G.*; 大木 康弘*; 滝沢 優*; 藤森 淳; 竹田 幸治; 藤森 伸一; 寺井 恒太*; 岡根 哲夫; et al.

Physical Review B, 78(15), p.155322_1 - 155322_4, 2008/10

https://doi.org/10.1103/PhysRevB.78.155322
 被引用回数：5 パーセンタイル：26.23(Materials Science, Multidisciplinary)

The electronic structure of Li-doped Ni$$_{1-x}$$Fe$$_x$$O has been investigated using photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS). The Ni $$2p$$ core-level PES and XAS spectra were not changed by Li doping. In contrast, the Fe$$^{3+}$$ intensity increased with Li doping relative to the Fe$$^{2+}$$ intensity. However, the increase of Fe$$^{3+}$$ is only $$sim 5%$$ of the doped Li content, suggesting that most of the doped holes enter the O $$2p$$ and/or the charge-transferred configuration Ni $$3d^8underline{L}$$. The Fe $$3d$$ partial density of states and the host valence-band emission near valence-band maximum increased with Li content, consistent with the increase of electrical conductivity. Based on these findings, percolation of bound magnetic polarons is proposed as an origin of the ferromagnetic behavior.

論文

Soft X-ray absorption and photoemission studies of ferromagnetic Mn-implanted 3$$C$$-SiC

Song, G.*; 小林 正起*; Hwang, J. I.*; 片岡 隆*; 滝沢 優*; 藤森 淳; 大河内 拓雄; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; et al.

Japanese Journal of Applied Physics, 47(9), p.7113 - 7116, 2008/09

https://doi.org/10.1143/JJAP.47.7113
 被引用回数：3 パーセンタイル：14.42(Physics, Applied)

We have performed X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and resonant photoemission spectroscopy (RPES) measurements of Mn-implanted 3$$C$$-SiC (3$$C$$-SiC:Mn) and carbon-incorporated Mn$$_{5}$$Si$$_{2}$$ (Mn$$_{5}$$Si$$_{2}$$:C). The Mn 2$$p$$ core-level XPS and XAS spectra of 3$$C$$-SiC:Mn and Mn$$_{5}$$Si$$_{2}$$:C were similar to each other and showed "intermediate" behaviors between the localized and itinerant Mn 3$$d$$ states. The intensity at the Fermi level was found to be suppressed in 3$$C$$-SiC:Mn compared with Mn$$_{5}$$Si$$_{2}$$:C. These observations are consistent with the formation of Mn$$_{5}$$Si$$_{2}$$:C clusters in the 3$$C$$-SiC host, as observed in a recent transmission electron microscopy study.

論文

Electronic structure of Ga$$_{1-x}$$Cr$$_{x}$$N and Si-doping effects studied by photoemission and X-ray absorption spectroscopy

Song, G.*; 小林 正起*; Hwang, J. I.*; 片岡 隆*; 滝沢 優*; 藤森 淳; 大河内 拓雄; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; et al.

Physical Review B, 78(3), p.033304_1 - 033304_4, 2008/07

https://doi.org/10.1103/PhysRevB.78.033304
 被引用回数：8 パーセンタイル：37.3(Materials Science, Multidisciplinary)

The electronic structure of the magnetic semiconductor Ga$$_{1-x}$$Cr$$_{x}$$N, and the effect of Si doping on it have been investigated by photoemission and soft X-ray absorption spectroscopy. We have confirmed that Cr in GaN is predominantly trivalent when substituting for Ga and that Cr 3$$d$$ states appear within the band gap of GaN just above the N 2$$p$$-derived valence-band maximum. As a result of Si doping, downward shifts of the core levels (except for Cr 2$$p$$) and the formation of new states near the Fermi level were observed, which we attribute to the upward chemical-potential shift and the formation of a small amount of Cr$$^{2+}$$ species caused by electron doping. Possibility of Cr-rich cluster growth by Si doping are discussed based on the spectroscopic and magnetization data.

論文

Photoemission and X-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)$$_3$$O$$_4$$ thin films exhibiting photoinduced magnetization

小林 正起*; 大木 康弘*; 滝沢 優*; Song, G. S.*; 藤森 淳; 竹田 幸治; 寺井 恒太*; 岡根 哲夫; 藤森 伸一; 斎藤 祐児; et al.

Applied Physics Letters, 92(8), p.082502_1 - 082502_3, 2008/02

https://doi.org/10.1063/1.2885080
 被引用回数：12 パーセンタイル：44.62(Physics, Applied)

By means of photoemission and X-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)$$_{3}$$O$$_{4}$$ thin films, which exhibits a cluster glass behavior with a spin-freezing temperature $$T_f$$ of $$sim 230$$ K and photo-induced magnetization (PIM) below $$T_f$$. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe$$^{3+}$$) and tetravalent (Ti$$^{4+}$$), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe$$^{2+}$$ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.

論文

Phase change observed in ultrathin Ba$$_{0.5}$$Sr$$_{0.5}$$TiO$$_3$$ films by in situ resonant photoemission spectroscopy

Lin, Y.-H.*; 寺井 恒太*; 和達 大樹*; 小林 正起*; 滝沢 優*; Hwang, J. I.*; 藤森 淳; Nan, C.-W.*; Li, J.-F.*; 藤森 伸一; et al.

Applied Physics Letters, 90(22), p.222909_1 - 222909_3, 2007/05

AA2007-0754.pdf:0.58MB

https://doi.org/10.1063/1.2745249
 被引用回数：6 パーセンタイル：26.43(Physics, Applied)

パルスレーザー堆積法によりNbをドープしたSrTiO$$_3$$(100)基板上にBa$$_{0.5}$$Sr$$_{0.5}$$TiO$$_3$$のエピタキシャル薄膜を作製し、室温と低温で価電子帯のTi 2p$$rightarrow$$3dの共鳴光電子分光スペクトルを測定した。その結果膜厚が2.8nm($$sim$$7ML)と2.0nm($$sim$$5ML)の間で大きな違いがみられ、強誘電転移の臨界膜厚が2.0-2.8nmの範囲にあることがわかった。

口頭

サファイア上に成長した単層酸化グラフェンのXAFSによる研究

圓谷 志郎; 本田 充紀; 滝沢 優*; 下山 巖; 楢本 洋*; 境 誠司; 社本 真一

no journal, , 

酸化グラフェンはグラフェンの大量合成を可能にする素材として研究が進んでいる物質である。発表者らは、基板上に形成した酸化グラフェン薄膜に金属イオンを吸着させ、吸着状態を表面科学手法により調べることにより、酸化グラフェンへの吸着機構を探索している。本研究では、サファイア基板上に作製した単層酸化グラフェン薄膜への原子構造やセシウムの吸着状態についてXAFSやXPSを用いて探索した。単層酸化グラフェンはサファイア基板上にCVD法で成長した単層グラフェンを酸化することにより作製した。Cs吸着前後の電子状態や原子構造を炭素および酸素のK吸収端(立命館大学SRセンター)、セシウムL3吸収端XAFS(KEK PF)により評価した。その結果、単層酸化グラフェン中のCOOHにセシウムが吸着することや酸化グラフェン1kgに対して650-850gものセシウムを吸着できることを明らかにした。

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