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論文

Large antisymmetric interlayer exchange coupling enabling perpendicular magnetization switching by an in-plane magnetic field

増田 啓人*; 関 剛斎*; 山根 結太*; Modak, R.*; 内田 健一*; 家田 淳一; Lau, Y.-C.*; 深見 俊輔*; 高梨 弘毅

Physical Review Applied (Internet), 17(5), p.054036_1 - 054036_9, 2022/05

https://doi.org/10.1103/PhysRevApplied.17.054036
 被引用回数：6 パーセンタイル：70.93(Physics, Applied)

反対称層間交換結合(AIEC)が最近発見され、人工反強磁性体(SAF)の傾角磁化の誘起を通じた磁化スイッチングにおいて極めて重要な役割を果たしている。本研究では、くさび形の層を持つ垂直磁化多層膜Pt/Co/Ir/Co/Ptにおける大きなAIECを報告をする。AIECの有効磁場は、対称的な層間交換結合に関連しており、AIECを強化するための指針を提供する。SAFに対する拡張Stoner-Wohlfarthモデルを開発し、その磁化スイッチングの重要な要素を明らかにする。理論的知識と実験結果を組み合わせることで、面内磁場のみによる垂直磁化スイッチングが達成される。

論文

High energy photon emission from wakefields

Farinella, D. M.*; Lau, C. K.*; Zhang, X. M.*; Koga, J. K.; Taimourzadeh, S.*; Hwang, Y.*; Abazajian, K.*; Canac, N.*; 戎崎 俊一*; Taborek, P.*; et al.

Physics of Plasmas, 23(7), p.073107_1 - 073107_10, 2016/07

https://doi.org/10.1063/1.4956450
 被引用回数：4 パーセンタイル：21.57(Physics, Fluids & Plasmas)

Experimental evidence has accumulated to indicate that wakefield acceleration (WFA) accompanies intense and sometimes coherent emission of radiation such as from betatron radiation. The investigation of this issue has additional impetus nowadays because we are learning (1) there is an additional acceleration process of the ponderomotive acceleration; (2) WFA may become relevant in much higher density regimes; (3) WFA has been proposed as the mechanism for extreme high energy cosmic ray acceleration and $$gamma$$ ray bursts for active galactic nuclei. These require us to closely examine the radiative mechanisms in WFA anew. We report studies of radiation from wakefield (self-injected betatron) and ponderomotive (laser field) in scalings of the frequency and intensity of the driver, as well as the plasma density.

論文

Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation

Lohrmann, A.*; Castelletto, S.*; Klein, J. R.*; 大島 武; Bosi, M.*; Negri, M.*; Lau, D. W. M.*; Gibson, B. C.*; Prawer, S.*; McCallum, J. C.*; et al.

Applied Physics Letters, 108(2), p.021107_1 - 021107_4, 2016/01

https://doi.org/10.1063/1.4939906
 被引用回数：39 パーセンタイル：82.59(Physics, Applied)

Creation and characterisation of single photon emitters near the surface of 4H- and 6H-silicon carbide bulk substrates and 3C-SiC epitaxially grown on silicon substrates were investigated. These single photon emitters can be created and stabilized by thermal annealing in an oxygen atmosphere at temperatures above 550 $$^{circ}$$C. Hydrofluoric acid (HF) treatment is shown to effectively annihilate the emission from defects and to restore an optically clean surface. However, the emission from the defects can be obtained after re-oxidation above 550 $$^{circ}$$C. By measuring using standard confocal microscopy techniques, the excited state lifetimes for the emitters are found to be in the nanosecond regime in all three polytypes, and the emission dipoles are aligned with the lattice.

論文

Atom-photon coupling from nitrogen-vacancy centres embedded in tellurite microspheres

Ruan, Y.*; Gibson, B. C.*; Lau, D. W. M.*; Greentree, A. D.*; Ji, H.*; Ebendorff-Heidepriem, H.*; Johnson, B. C.*; 大島 武; Monro, T. M.*

Scientific Reports (Internet), 5, p.11486_1 - 11486_7, 2015/06

https://doi.org/10.1038/srep11486
 被引用回数：5 パーセンタイル：29.59(Multidisciplinary Sciences)

A technique for creating high quality tellurite microspheres with embedded nano-diamonds (NDs) containing nitrogen-vacancy (NV) centers was developed. TZN tellurite glass (TeO$$_{2}$$-ZnO-Na$$_{2}$$O) was fabricated in-house using the melt-quench technique and was formed to be glass fiber with a diameter of 0.16 mm. During this process, NDs with NV centers which were created by electron irradiation at 2 MeV were added into TZN tellurite glass above 690 $$^{circ}$$C. To obtain uniformly dispersed ND solutions, the NDs were processed using strong acid reflux and ultra-sonication before the mixture with TZN tellurite glass. This method can realize very bright fluorescence of the NVs in the NDs at room temperature. It is concluded that this new approach can be applied to a robust way of creating cavities for use in quantum and sensing applications.

論文

The ITER-QUELL, a quench propagation experiment on a long length CICC with central channel

Anghel, A.*; 高橋 良和; Smith, S.*; Pourrahimi, S.*; Zhelamskij, M.*; Blau, B.*; Fuchs, A.*; Heer, B.*; 濱田 一弥; Fujisaki, H.*; et al.

Fusion Technology 1996, p.185 - 190, 1996/00

ITERタスクの一貫として行われたクエンチ試験(QUELL)は、1/6の縮小導体を約100m用いて導体がクエンチした時の導体のふるまいを観測し、このデータを用いてコンピュータの解析コードを確立することと、クエンチ検出システムを開発することを目的として、行われた。本論文においては、クエンチ時の常伝導部の伝播の結果(伝播速度、温度上昇、圧力上昇等)及びクエンチ検出システムの性能について報告する。

口頭

High energy photon emission from wakefields and its signatures in astrophysical Blazars

Farinella, D.*; Zhang, X.*; Lau, C.*; Taimourzadeh, S.*; Hwang, Y.*; Koga, J. K.; 戎崎 俊一*; 田島 俊樹*

no journal, , 

Episodic eruptions of accretion disks of AGNs (and Blazars) due to the Magneto-Rotational-Instability are related to the excitation of intense Alfv$'e$n waves and their subsequently mode converted EM pulses. These intense pulses are related to the emission of bursts of $$gamma$$ rays and extreme high energy cosmic ray (EHECR) genesis in AGN and Blazars. Wakefield acceleration and pondermotive acceleration of electrons give rise to $$gamma$$ ray emissions of the above through synchrotron radiation which can undergo inverse-Compton scattering to attain high X-ray energies. We study additional emissions of $$gamma$$ rays by the betatron oscillations and QED radiative processes in the intense accelerating fields.

口頭

高温熱処理したSiC中に存在する単一光子源

大島 武; Lohrmann, A.*; Johnson, B. C.*; Castelletto, S.*; 小野田 忍; 牧野 高紘; 武山 昭憲; Klein, J. R.*; Bosi, M.*; Negri, M.*; et al.

no journal, , 

量子スピントロニクスや量子フォトニクスへの応用が期待される炭化ケイ素半導体(SiC)中の単一光子源(SPS)に関して、デバイス作製の際に用いる高温熱処理といったプロセス後にも安定に存在するSPSの探索を行った。共焦点蛍光顕微鏡(CFM)観察の結果、1600$$^{circ}$$C以上での熱処理後も550$$sim$$600nmの波長帯に室温においても高輝度で発光特性を示すSPSが存在することが確認された。加えて、未熱処理のSiC基板のCFM観察を行ったところ、非常に少量ではあるが同様なSPSが存在することも判明したが、発光は不安定であり、数秒間の観察中に発光が消失してしまうことが見いだされた。そこで、熱処理温度(酸素中、5分間)とSPSの発光の安定性の関係を調べたところ、550$$^{circ}$$C以上の熱処理で発光が安定化することが明らかとなった。

口頭

Visible range photoluminescence from single photon sources in 3C, 4H and 6H silicon carbide

Lohrmann, A.*; Castelletto, S.*; Klein, J. R.*; Bosi, M.*; Negri, M.*; Lau, D. W. M.*; Gibson, B. C.*; Prawer, S.*; McCallum, J. C.*; 大島 武; et al.

no journal, , 

The single photon sources (SPSs) in the visible spectral region were fabricated near the surface of semi-insulating (SI) 4H-silicon carbide (SiC), SI 6H-SiC substrates and 3C-SiC epitaxial films by annealing in dry oxygen. The photoluminescence (PL) with high intensity was observed from samples after oxygen annealing above 550 $$^{circ}$$C although blinking characteristics of PL were observed from samples annealed below 550 $$^{circ}$$C. Also, the samples annealed above 550 $$^{circ}$$C showed blinking characteristics after removing oxygen atoms terminating the surface by HF-etching. Therefore, we can conclude that the oxygen termination is important to obtain stable PL characteristics from the SPSs near the surface of SiC.

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