JAEA
  • help
  • PC | SP
  • JP | EN
          
検索対象：     
報告書番号：
※ 半角英数字
 年 ～ 
 年
全てクリア
検索結果：　26 件中 1件目～20件目を表示

発表形式

Initialising ...

選択項目を絞り込む

掲載資料名

Initialising ...

発表会議名

Initialising ...

筆頭著者名

Initialising ...

キーワード

Initialising ...

使用言語

Initialising ...

発行年

Initialising ...

開催年

Initialising ...

選択した検索結果をダウンロード

論文

Origin of magnetically dead layers in spinel ferrites $$M$$Fe$$_2$$O$$_4$$ grown on Al$$_2$$O$$_3$$; Effects of postdeposition annealing studied by XMCD

野中 洋亮*; 若林 勇希*; 芝田 悟朗; 坂本 祥哉*; 池田 啓祐*; Chi, Z.*; Wan, Y.*; 鈴木 雅弘*; 田中 新*; 田中 雅明*; et al.

Physical Review Materials (Internet), 7(4), p.044413_1 - 044413_10, 2023/04

https://doi.org/10.1103/PhysRevMaterials.7.044413
 被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)

We study the electronic and magnetic states of as-grown and annealed $$M$$Fe$$_2$$O$$_4$$(111)/Al$$_2$$O3(111) ($$M =$$Co, Ni) thin films with various thicknesses grown on Si(111) substrates with the $$gamma$$-Al$$_2$$O$$_3$$(111)buffer layers by using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD), to investigate magnetically dead layers in these films. Although the magnetically dead layers in the as-grown samples are formed near the interface with the Al$$_2$$O$$_3$$ buffer layer, we reveal that ferrimagnetic order is partially recovered by postdeposition annealing at 973 K for 48 hours in air. By analyzing the line shapes of the XAS and XMCD spectra, we conclude that, in the dead layers, there are a significant number of vacancies at the $$T_d$$ sites of the spinel structure, which may be the microscopic origin of the degraded ferrimagnetic order in the $$M$$Fe$$_2$$O$$_4$$ thin films.

論文

Alternation of magnetic anisotropy accompanied by metal-insulator transition in strained ultrathin manganite heterostructures

小林 正起*; Anh, L. D.*; 鈴木 雅弘*; 金田-高田 真悟*; 竹田 幸治; 藤森 伸一; 芝田 悟朗*; 田中 新*; 田中 雅明*; 大矢 忍*; et al.

Physical Review Applied (Internet), 15(6), p.064019_1 - 064019_10, 2021/06

https://doi.org/10.1103/PhysRevApplied.15.064019
 被引用回数：4 パーセンタイル：27.71(Physics, Applied)

A fundamental understanding of the interfacial magnetic properties in ferromagnetic heterostructures is essential for utilizing ferromagnetic materials for spintronic device applications. Here, we investigate the interfacial magnetic and electronic structures of epitaxial single-crystalline LaAlO$$_3$$(LAO)/La$$_{0.6}$$Sr$$_{0.4}$$MnO$$_3$$(LSMO)/Nb:SrTiO$$_3$$(Nb:STO) heterostructures with varying LSMO layer thicknesses, in which the magnetic anisotropy strongly changes with the LSMO thickness due to the delicate balance between strains originating from both the Nb:STO and LAO layers, using X-ray magnetic circular dichroism and photoemission spectroscopy. We successfully detect the clear change of the magnetic behavior of the Mn ions concomitant with the thickness-dependent metal-insulator transition. Our results suggest that the double-exchange interaction induces ferromagnetism in the metallic LSMO film under tensile strain caused by the STO substrate, while the superexchange interaction determines the magnetic behavior in the insulating LSMO film under compressive strain originating from the top LAO layer. The change in strain, depending on LSMO layer thickness, is confirmed by scanning transmission electron microscopy. Based on those findings, the formation of a magnetic dead layer near the LAO/LSMO interface is attributed to competition between the superexchange interaction via Mn $$3d_{3z^2-r^2}$$ orbitals under compressive strain and the double-exchange interaction via the $$3d_{x^2-y^2}$$ orbitals. These findings provide key aspects of ferromagnetic oxide heterostructures for the development of spintronic device applications.

論文

Direct observation of the magnetic ordering process in the ferromagnetic semiconductor Ga$$_{1-x}$$Mn$$_{x}$$As via soft X-ray magnetic circular dichroism

竹田 幸治; 大矢 忍*; Pham, N. H.*; 小林 正起*; 斎藤 祐児; 山上 浩志; 田中 雅明*; 藤森 淳*

Journal of Applied Physics, 128(21), p.213902_1 - 213902_11, 2020/12

https://doi.org/10.1063/5.0031605
 被引用回数：8 パーセンタイル：44.34(Physics, Applied)

In order to understand the mechanism of the ferromagnetism in Ga$$_{1-x}$$Mn$$_{x}$$As ((Ga,Mn)As), we have investigated the magnetic behavior on a microscopic level through systematic temperature ($$T$$) and magnetic-field ($$H$$) dependent soft X-ray magnetic circular dichroism (XMCD) experiments at the Mn $$L_mathrm{2,3}$$ absorption edges. The $$T$$ and $$H$$ dependences of XMCD intensities have been analyzed using a model consisting of the ferromagnetic (FM), paramagnetic, and superparamagnetic (SPM) components. Intriguingly, we have found a common behavior for the ferromagnetic ordering process in (Ga,Mn)As samples with different Mn concentrations and different Curie temperature ($$T_mathrm{C}$$) values. In particular, the SPM component develops well above $$T_mathrm{C}$$, indicating that local FM regions are formed well above $$T_mathrm{C}$$. The present findings indicate that the onset of ferromagnetic ordering is triggered by local electronic states around the substitutional Mn ions. Insight into the most representative ferromagnetic semiconductor, (Ga,Mn)As, will be an important step in understanding the mechanism of ferromagnetic ordering in various ferromagnetic semiconductor families.

論文

Evolution of Fe 3$$d$$ impurity band state as the origin of high Curie temperature in the $$p$$-type ferromagnetic semiconductor (Ga,Fe)Sb

武田 崇仁*; 坂本 祥哉*; 荒木 恒星*; 藤澤 唯太*; Anh, L. D.*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; 藤森 淳*; 田中 雅明*; et al.

Physical Review B, 102(24), p.245203_1 - 245203_8, 2020/12

https://doi.org/10.1103/PhysRevB.102.245203
 被引用回数：7 パーセンタイル：44.34(Materials Science, Multidisciplinary)

(Ga$$_{1-x}$$,Fe$$_x$$)Sb is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature (Tc) is above 300 K when the Fe concentration $$x$$ is equal to or higher than 0.20. However, the origin of the high Tc in (Ga,Fe)Sb remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and first-principles calculations to investigate the x dependence of the Fe 3$$d$$ states in (Ga$$_{1-x}$$,Fe$$_x$$)Sb ($$x$$ = 0.05, 0.15, and 0.25) thin films. The observed Fe 2$$p$$-3$$d$$ RPES spectra reveal that the Fe-3$$d$$ impurity band (IB) crossing the Fermi level becomes broader with increasing $$x$$, which is qualitatively consistent with the picture of double-exchange interaction. Comparison between the obtained Fe-3$$d$$ partial density of states and the first-principles calculations suggests that the Fe-3$$d$$ IB originates from the minority-spin ($$downarrow$$) $$e$$ states. The results indicate that enhancement of the double-exchange interaction between $$e_{downarrow}$$ electrons with increasing $$x$$ is the origin of the high Tc in (Ga,Fe)Sb.

論文

Electronic structure of the high-$$T_{rm C}$$ ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies

坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.

Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07

https://doi.org/10.1103/PhysRevB.100.035204

The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature $$T_{rm C}$$ can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3$$d^{6}$$ contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3$$d$$ electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3$$d$$ states have a finite contribution to the density of states at the Fermi energy. These states, presumably consisting of majority-spin $$p$$-$$d$$ hybridized states or minority-spin e states, would be responsible for the ferromagnetic order in this material.

論文

Electronic structure of the high-$$T_{rm C}$$ ferromagnetic semiconductor (Ga,Fe)Sb; X-ray magnetic circular dichroism and resonance photoemission spectroscopy studies

坂本 祥哉*; Tu, N. T.*; 竹田 幸治; 藤森 伸一; Hai, P. N.*; Anh, L. D.*; 若林 勇希*; 芝田 悟朗*; 堀尾 眞史*; 池田 啓祐*; et al.

Physical Review B, 100(3), p.035204_1 - 035204_8, 2019/07

https://doi.org/10.1103/PhysRevB.100.035204
 被引用回数：16 パーセンタイル：66.08(Materials Science, Multidisciplinary)

The electronic structure and the magnetism of the ferromagnetic semiconductor (Ga,Fe)Sb, whose Curie temperature $$T_{rm C}$$ can exceed room temperature, were investigated by means of X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and resonance photoemission spectroscopy (RPES). The line-shape analyses of the XAS and XMCD spectra suggest that the ferromagnetism is of intrinsic origin. The orbital magnetic moments deduced using XMCD sum rules were found to be large, indicating that there is a considerable 3$$d^{6}$$ contribution to the ground state of Fe. From RPES, we observed a strong dispersive Auger peak and nondispersive resonantly enhanced peaks in the valence-band spectra. The latter is a fingerprint of the correlated nature of Fe 3$$d$$ electrons, whereas the former indicates their itinerant nature. It was also found that the Fe 3$$d$$ states have a finite contribution to the density of states at the Fermi energy. These states would be responsible for the ferromagnetic order in this material.

論文

Cation distribution and magnetic properties in ultrathin (Ni$$_{1-x}$$Co$$_{x}$$)Fe$$_{2}$$O$$_{4}$$ (x=0-1) layers on Si(111) studied by soft X-ray magnetic circular dichroism

若林 勇希*; 野中 洋亮*; 竹田 幸治; 坂本 祥哉*; 池田 啓祐*; Chi, Z.*; 芝田 悟朗*; 田中 新*; 斎藤 祐児; 山上 浩志; et al.

Physical Review Materials (Internet), 2(10), p.104416_1 - 104416_12, 2018/10

https://doi.org/10.1103/PhysRevMaterials.2.104416
 被引用回数：10 パーセンタイル：37.66(Materials Science, Multidisciplinary)

We study the electronic structure and magnetic properties of epitaxial (Ni$$_{1-x}$$Co$$_{x}$$)Fe$$_{2}$$O$$_{4}$$(111) layers with thicknesses $$d$$ = 1.7 - 5.2 nm grown on Al$$_{2}$$O$$_{3}$$(111)/Si(111) structures. We revealed the crystallographic (octahedral $$O_{h}$$ or tetrahedral $$T_{d}$$) sites and the valences of the Fe, Co, and Ni cations using experimental soft X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectra and configuration-interaction cluster-model calculation.

論文

Electronic structure and correlation in $$beta$$-Ti$$_3$$O$$_5$$ and $$lambda$$-Ti$$_3$$O$$_5$$ studied by hard X-ray photoelectron spectroscopy

小林 啓介*; 田口 宗孝*; 小畠 雅明; 田中 健司*; 所 裕子*; 大門 寛*; 岡根 哲夫; 山上 浩志; 池永 英司*; 大越 慎一*

Physical Review B, 95(8), p.085133_1 - 085133_7, 2017/02

AA2017-0038.pdf:0.98MB

https://doi.org/10.1103/PhysRevB.95.085133
 被引用回数：15 パーセンタイル：56.08(Materials Science, Multidisciplinary)

We have conducted hard X-ray photoelectron spectroscopy investigations of the electronic structure changes and electron correlation phenomena which take place upon the photoinduced reversible phase transition between $$beta$$- and $$lambda$$-Ti$$_3$$O. From valence band spectra of $$beta$$- and $$lambda$$-Ti$$_3$$O$$_5$$, we have identified the bipolaron caused by the $$sigma$$-type bonding of $$d_{xy}$$ orbitals in $$beta$$-Ti$$_3$$O$$_5$$ and the $$pi$$ stacking between the $$d_{xy}$$ orbitals between different Ti sites in $$lambda$$-Ti$$_3$$O$$_5$$, previously predicted by $textit{ab initio}$ calculations. On the other hand, the Ti $$2p$$ and Ti $$1s$$ core level spectra exhibit nonlocal screening satellite features, which are typical spectroscopic signs of strong electron correlation in the coherent Ti $$t_{2g}$$ states. Correlation in the valence band also manifests to reduce the plasmon energy, which results in an enhancement of the valence electron mass by a factor of 2.7.

論文

Origin of robust nanoscale ferromagnetism in Fe-doped Ge revealed by angle-resolved photoemission spectroscopy and first-principles calculation

坂本 祥哉*; 若林 勇希*; 竹田 幸治; 藤森 伸一; 鈴木 博人*; 伴 芳祐*; 山上 浩志; 田中 雅明*; 大矢 忍*; 藤森 淳*

Physical Review B, 95(7), p.075203_1 - 075203_5, 2017/02

https://doi.org/10.1103/PhysRevB.95.075203
 被引用回数：9 パーセンタイル：42.75(Materials Science, Multidisciplinary)

Ge$$_{1-x}$$Fe$$_x$$ (Ge:Fe) shows ferromagnetic behavior up to a relatively high temperature of 210 K and hence is a promising material for spintronic applications compatible with Si technology. We have studied its underlying electronic structure by soft X-ray angle-resolved photoemission spectroscopy measurements and first-principles supercell calculation. We observed finite Fe 3$$d$$ components in the states at the Fermi level ($$Erm_F$$) in a wide region of momentum space, and the $$Erm_F$$ was located $$sim$$0.35 eV above the valence-band maximum of the host Ge. Our calculation indicates that the $$Erm_F$$ is also within the deep acceptor-level impurity band induced by the strong $$p$$-$$d$$($$t_2$$) hybridization. We conclude that the additional minority-spin $$d(e)$$ electron characteristic of the Fe$$^{2+}$$ state is responsible for the short-range ferromagnetic coupling between Fe atoms.

論文

Origin of the large positive magnetoresistance of Ge$$_{1-x}$$Mn$$_{x}$$ granular thin films

若林 勇希*; 秋山 了太*; 竹田 幸治; 堀尾 眞史*; 芝田 悟朗*; 坂本 祥哉*; 伴 芳祐*; 斎藤 祐児; 山上 浩志; 藤森 淳*; et al.

Physical Review B, 95(1), p.014417_1 - 014417_6, 2017/01

https://doi.org/10.1103/PhysRevB.95.014417
 被引用回数：10 パーセンタイル：45.87(Materials Science, Multidisciplinary)

Ge$$_{1_x}$$Mn$$_x$$ (GeMn) granular thin films are a unique and promising material for spintronic applications owing to their large positive magnetoresistance (MR). The microscopic origin of the MR has not yet been clarified. Here, we develop a method to separately investigate the magnetic properties of the nanoparticles and the matrix, utilizing the extremely high sensitivity of X-ray magnetic circular dichroism (XMCD) to the local magnetic state of each atom. We find that the MR ratio is proportional to the product of the magnetizations originating from the nanoparticles and the matrix. This result indicates that the spin-polarized holes in the nanoparticles penetrate into the matrix and that these holes undergo first order magnetic scattering by the paramagnetic Mn atoms in the matrix, which induces the large MR.

論文

Room-temperature local ferromagnetism and its nanoscale expansion in the ferromagnetic semiconductor Ge$$_{1-x}$$Fe$$_{x}$$

若林 勇希*; 坂本 祥哉*; 竹田 幸治; 石上 啓介*; 高橋 文雄*; 斎藤 祐児; 山上 浩志; 藤森 淳*; 田中 雅明*; 大矢 忍*

Scientific Reports (Internet), 6, p.23295_1 - 23295_9, 2016/03

AA2016-0503.pdf:1.66MB

https://doi.org/10.1038/srep23295
 被引用回数：20 パーセンタイル：66.31(Multidisciplinary Sciences)

We investigate the local electronic structure and magnetic properties of the group-IV-based ferromagnetic semiconductor, Ge$$_{1-x}$$Fe$$_{x}$$ (GeFe), using soft X-ray magnetic circular dichroism. Our results show that the doped Fe 3$$d$$ electrons are strongly hybridized with the Ge 4$$p$$ states, and have a large orbital magnetic moment relative to the spin magnetic moment, namely $$m_{rm orb}$$/$$m_{rm spin}$$ $$approx$$ 0.1. We find that nanoscale local ferromagnetic regions, which are formed through ferromagnetic exchange interactions in the high-Fe-content regions of the GeFe films, exist even at room temperature, well above the Curie temperature of 20 - 100K. We observe the intriguing nanoscale expansion of the local ferromagnetic regions with decreasing temperature, followed by a transition of the entire film into a ferromagnetic state at the Curie temperature.

論文

Magnetization process of the $$n$$-type ferromagnetic semiconductor (In,Fe)As:Be studied by X-ray magnetic circular dichroism

坂本 祥哉*; Anh, L. D.*; Hai, P. N.*; 芝田 悟朗*; 竹田 幸治; 小林 正起*; 高橋 文雄*; 小出 常晴*; 田中 雅明*; 藤森 淳*

Physical Review B, 93(3), p.035203_1 - 035203_6, 2016/01

AA2016-0502.pdf:1.1MB

https://doi.org/10.1103/PhysRevB.93.035203
 被引用回数：18 パーセンタイル：63.01(Materials Science, Multidisciplinary)

In order to investigate the mechanism of ferromagnetic ordering in the new $$n$$-type magnetic semiconductor (In,Fe)As codoped with Be, we have performed X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XMCD) studies. The spectral line shapes suggest that the ferromagnetism is intrinsic, originating from Fe atoms incorporated into the zinc-blende-type InAs lattice. The magnetization curves of Fe measured by XMCD were well reproduced by the superposition of a Langevin function representing superparamagnetic (SPM) behavior of nanoscale ferromagnetic domains and a $$T$$-linear function representing Curie-Weiss paramagnetism even much above the Curie temperatures. The data at 20 K showed a deviation from the Langevin behavior, suggesting a gradual establishment of macroscopic ferromagnetism on lowering temperature. The existence of nanoscale ferromagnetic domains indicated by the SPM behavior suggests spatial fluctuations of Fe concentration on the nanoscale.

論文

Current status of the driver laser system for intense terahertz wave generation

田中 桃子; 越智 義浩; 小菅 淳; 岡田 大; 森 道昭; 桐山 博光; 坪内 雅明; 永島 圭介

JAEA-Conf 2014-001, p.32 - 33, 2014/09

https://doi.org/10.11484/jaea-conf-2014-001

テラヘルツ波発生用ドライバーレーザーとして、Yb:YAGシンディスクを利得媒質として用いた高強度キロヘルツレーザーシステムを構築した。再生増幅器は4バウンスの構成とし、最大10mJの出力を得た。また、圧縮後のパルスを用いてLiNbO$$_{3}$$結晶によるテラヘルツ波発生のデモンストレーションを行った。

論文

Spin and orbital magnetic moments of Fe in the $$n$$-type ferromagnetic semiconductor (In,Fe)As

小林 正起*; Anh, L. D.*; Hai, P. N.*; 竹田 幸治; 坂本 祥哉*; 門野 利治*; 岡根 哲夫; 斎藤 祐児; 山上 浩志; 原田 慈久*; et al.

Applied Physics Letters, 105(3), p.032403_1 - 032403_4, 2014/07

AA2015-0418.pdf:0.82MB

https://doi.org/10.1063/1.4890733
 被引用回数：6 パーセンタイル：26.85(Physics, Applied)

The electronic and magnetic properties of Fe atoms in the ferromagnetic semiconductor (In,Fe)As codoped with Be have been studied by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at the Fe $$L_{2,3}$$ edge. The XAS and XMCD spectra showed simple spectral line shapes similar to Fe metal, but the ratio of the orbital and spin magnetic moments estimated using the XMCD sum rules was significantly larger than that of Fe metal, indicating a significant orbital moment of Fe 3$$d$$ electrons in (In,Fe)As:Be. The XMCD intensity as a function of magnetic field indicated hysteretic behavior of the superparamagnetic-like component due to discrete ferromagnetic domains. VC

論文

Unveiling the impurity band induced ferromagnetism in the magnetic semiconductor (Ga,Mn)As

小林 正起*; 宗田 伊理也*; 竹田 幸治; 原田 慈久*; 藤森 淳*; Krempask$'y$, J.*; Schmitt, T.*; 大矢 忍*; 田中 雅明*; 尾嶋 正治*; et al.

Physical Review B, 89(20), p.205204_1 - 205204_8, 2014/05

https://doi.org/10.1103/PhysRevB.89.205204
 被引用回数：78 パーセンタイル：92.27(Materials Science, Multidisciplinary)

(Ga,Mn)As is a paradigm of a diluted magnetic semiconductor which shows ferromagnetism induced by doped hole carriers. With a few controversial models emerging from numerous experimental and theoretical studies, the mechanism of the ferromagnetism in (Ga,Mn)As still remains a puzzling enigma. In this article, we use soft X-ray angle-resolved photoemission spectroscopy to positively identify the ferromagnetic Mn 3d-derived impurity band (IB) in (Ga,Mn)As. The band appears dispersionless and hybridized with the light-hole band of the host GaAs. These findings conclude the picture of the valence-band structure of (Ga,Mn)As disputed for more than a decade. The nondispersive character of the IB and its location in vicinity of the valence-band maximum indicate that the Mn 3d-derived IB is formed as a split-off Mn-impurity state predicted by the Anderson.

論文

軟X線磁気円二色性による希薄磁性半導体Ga$$_{1-x}$$Mn$$_{x}$$AsのMnイオンの磁気的相互作用の研究

竹田 幸治; 小林 正起*; 岡根 哲夫; 大河内 拓雄*; 岡本 淳*; 斎藤 祐児; 小林 啓介*; 山上 浩志; 藤森 淳*; 田中 新*; et al.

放射光, 22(4), p.202 - 209, 2009/07

http://ci.nii.ac.jp/naid/10025009601

SPring-8 BL23SUで改良・整備を進めてきた軟X線磁気円二色性装置を用いて、希薄磁性半導体Ga$$_{1-x}$$Mn$$_{x}$$AsのMn元素の磁気的特性を系統的な温度・磁場依存性測定を行って調べた。その結果、Gaと置換されたMnイオンと結晶格子の隙間に入り込んだMnイオンの間には反強磁性相互作用が存在しており、キュリー温度と結晶格子の隙間に入り込んだMnイオンの量とは明らかに相関していて、Gaと置換されたMnイオンの強磁性秩序を結晶格子の隙間に入り込んだMnイオンが阻害していることがわかった。

論文

Nature of magnetic coupling between Mn ions in as-grown Ga$$_{1-x}$$Mn$$_{x}$$As studied by X-ray magnetic circular dichroism

竹田 幸治; 小林 正起*; 岡根 哲夫; 大河内 拓雄; 岡本 淳*; 斎藤 祐児; 小林 啓介*; 山上 浩志; 藤森 淳; 田中 新*; et al.

Physical Review Letters, 100(24), p.247202_1 - 247202_4, 2008/06

https://doi.org/10.1103/PhysRevLett.100.247202
 被引用回数：39 パーセンタイル：82.16(Physics, Multidisciplinary)

希薄磁性半導体(DMS)Ga$$_{1-x}$$Mn$$_{x}$$Asは、半導体スピントロニクス分野で注目を集めているが、室温強磁性は達成されていない。現状の試料作成技術では、MnイオンはGaイオンと置換される一方で、GaAs格子間にも侵入してしまい、この格子間に侵入したMnイオンの役割(影響)が不明であった。格子間に侵入した磁性イオンに関する同様の問題は、他のDMSにも多く存在する。今回の詳細なXMCD測定によって、格子間に侵入したMnイオンが、Gaイオンと置換されたMnイオン間の強磁性秩序の妨げになっていることが明らかになった。これは、格子間に侵入した磁性イオンの排除が多くのDMSの室温強磁性達成のために不可欠であるという試料作成に対する明確な方針を示すものである。

報告書

地震ハザード評価コードSHEATの使用手引

蛯沢 勝三; 田中 歳明*; 高荷 道雄*; 近藤 雅明; 阿部 清治

JAERI-Data/Code 94-009, 135 Pages, 1994/08

JAERI-Data-Code-94-009.pdf:4.05MB

SHEATコードは、原子力発電所の地震PSAで必要なタスクの1つである確率論的地震ハザード解析のための計算コードである。地震ハザードは、特定サイトでの地震動レベル毎の年当り超過発生頻度と定義される。SHEATコードで、地震ハザードは次の2ステップで計算される。(1)対象サイト周辺での地震発生のモデル化。対象サイト周辺での将来の地震発生(発生位置、マグニチュード及び発生頻度)を、歴史地震データ、活断層データ及び専門家の技術的判断に基づきモデル化する。(2)対象サイトにおける確率論的地震ハザードの計算。まず、(1)での各地震がもたらす対象サイトでの地震動を、地震動距離減衰式とその標準偏差を用いて計算する。次いで、地震動レベル毎の発生頻度をすべての地震について足し合わせることにより当該サイトの地震ハザードを計算する。本報告書は、SHEATコードの使用手引であり、以下を記述している。(1)SHEATコードの概要、(2)サブプログラムの機能と計算モデル、(3)入出力データの説明、(4)サンプル計算の結果。原研では既に、SHEATコードを我が国の種々の原子力発電所サイトに広範に適用し、各サイトでの地震ハザードを評価している。

口頭

Ga$$_{1-x}$$Mn$$_{x}$$Asの内殻吸収磁気円二色性による磁気的相互作用の研究

竹田 幸治; 小林 正起*; 岡根 哲夫; 大河内 拓雄; 岡本 淳*; 斎藤 祐児; 小林 啓介*; 山上 浩志; 藤森 淳; 田中 新*; et al.

no journal, , 

希薄磁性半導体Ga$$_{1-x}$$Mn$$_{x}$$Asは、半導体スピントロニクス分野で注目を集めているが、室温強磁性は達成されていない。現状の試料作成技術では、MnイオンはGaイオンと置換される一方で、GaAs格子間にも侵入してしまい、この格子間に侵入したMnイオンの役割影響が不明であった。格子間に侵入した磁性イオンに関する同様の問題は、他の希薄磁性半導体にも多く存在する。今回の内殻吸収磁気円二色性の詳細な温度・磁場依存性測定によって、格子間に侵入したMnイオンが、Gaイオンと置換されたMnイオン間の強磁性秩序の妨げになっていることが明らかになった。これは、格子間に侵入した磁性イオンの排除が室温強磁性達成のために不可欠であるという試料作成に対する明確な方針を示すものである。

口頭

次世代レーザー開発研究グループの総括及び次期中期計画の方針

杉山 僚; 桐山 博光; 越智 義浩; 田中 桃子; 中井 善基; 笹尾 一; 立野 亮; 岡田 大; 小菅 淳; 坪内 雅明

no journal, , 

原子力機構次世代レーザー開発研究グループにおける今期の中心開発課題は、超短パルスレーザーのJ-KAREN及びTOPAZの高度化である。J-KARENにおいては、ピーク出力500TW相当の高強度レーザーパルス光の発生に成功するとともに、10の10乗台を超える高コントラスト化を達成した。また、TOPAZでは、0.1Hz動作にて、現在1ビームあたり約15Jのパルス出力を発生した。また、光ネット事業(昨年8月開始)におけるQUADRA:高品位高輝度光源(Quality Ultra ADvanced RAdiation Source)開発に着手した。当事業は、高出力LD励起型のkHz級高平均出力超短パルスレーザー開発である。22年度からの原子力機構の次期中期5か年計画における新規光源開発を行ううえで、QUADRA開発は欠かせない。

26 件中 1件目～20件目を表示