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Work function lowering of LaB$$_{6}$$ by monolayer hexagonal boron nitride coating for improved photo- and thermionic-cathodes

山口 尚人*; 遊佐 龍之介*; Wang, G.*; Pettes, M. T.*; Liu, F.*; 津田 泰孝; 吉越 章隆; 虻川 匡司*; Moody, N. A.*; 小川 修一*

Applied Physics Letters, 122(14), p.141901_1 - 141901_7, 2023/04

 被引用回数:0 パーセンタイル:0(Physics, Applied)



Magnetization switching process by dual spin-orbit torque in interlayer exchange-coupled systems

増田 啓人*; 山根 結太*; 関 剛斎*; Raab, K.*; 土肥 昂尭*; Modak, R.*; 内田 健一*; 家田 淳一; Kl$"a$ui, M.*; 高梨 弘毅

Applied Physics Letters, 122(16), p.162402_1 - 162402_7, 2023/04


We report current-induced magnetization switching in Pt/Co/Ir/Co/Pt multilayers with different Ir layer thicknesses ($$t_mathrm{Ir}$$), where the perpendicularly magnetized Co layers are coupled ferromagnetically or antiferromagnetically through an interlayer exchange coupling and are sandwiched by the Pt spin Hall layers. The domain structures formed during switching vary depending on the magnetization alignment, i.e., ferromagnetically coupled or antiferromagnetically coupled configuration. These results clarify the macroscopic picture of switching process for interlayer exchange-coupled systems. The local picture of the switching process is also examined by a numerical calculation based on a macrospin model, which reveals the switching dynamics triggered by dual spin-orbit torque for both antiferromagnetically and ferromagnetically coupled cases. The numerical calculation shows that the dual spin-orbit torque from the two Pt layers effectively acts on the two Co layers not only for the antiferromagnetically coupled case but also for the ferromagnetically coupled one. Our findings deepen the under- standing of the switching mechanism in a magnetic multilayer and provide an avenue to design spintronic devices with more efficient spin-orbit torque switching.


Thermal stability of non-collinear antiferromagnetic Mn$$_3$$Sn nanodot

佐藤 佑磨*; 竹内 祐太郎*; 山根 結太*; Yoon, J.-Y.*; 金井 駿*; 家田 淳一; 大野 英男*; 深見 俊輔*

Applied Physics Letters, 122(12), p.122404_1 - 122404_5, 2023/03

 被引用回数:0 パーセンタイル:0(Physics, Applied)

$$D0_{19}$$-Mn$$_3$$Sn, an antiferromagnet having a non-collinear spin structure in a kagome lattice, has attracted great attention owing to various intriguing properties such as large anomalous Hall effect. Stability of magnetic state against thermal fluctuation, characterized in general by the thermal stability factor $$Delta$$, has been well studied in ferromagnetic systems but not for antiferromagnets. Here we study $$Delta$$ of the antiferromagnetic Mn$$_3$$Sn nanodots as a function of their diameter $$D$$. To obtain $$Delta$$, we measure the switching probability as a function of pulse-field amplitude and analyze the results based on a model developed by accounting for two and six-fold magnetic anisotropies in the kagome plane. We observe no significant change in $$Delta$$ down to $$D = 300$$ nm below which it decreases with $$D$$. The obtained $$D$$ dependence is well explained by a single-domain and nucleation-mediated reversal models. These findings provide a basis to understand the thermal fluctuation and reversal mechanism of antiferromagnets for device application.


Shapiro steps in charge-density-wave states driven by ultrasound

森 道康; 前川 禎通

Applied Physics Letters, 122(4), p.042202_1 - 042202_5, 2023/01

 被引用回数:0 パーセンタイル:0(Physics, Applied)

We show that ultrasound can induce the Shapiro steps (SS) in the charge-density-wave (CDW) state. When ultrasound with frequency $$omega$$ and a dc voltage are applied, the SS occur at the current $$Ipropto nomega$$ with integer $$n$$. Even and odd multiples of SS are represented by two couplings between the CDW and ultrasound. Although an ac voltage bias with frequency $$omega$$ induces the SS at $$Ipropto nomega$$, the ultrasound bias enhances the odd multiples more strongly than the even ones. This is the difference between the ultrasound and the ac voltage. Since the SS cause abrupt peaks in the $$dV/dI$$, the extreme changes in the $$I-V$$ curve will be applied to a very sensitive ultrasound detector.


Laser-fluence dependence of resonance-enhanced multiphoton reduction of trivalent europium

松田 晶平; 中島 信昭*; 横山 啓一; 谷口 誠治*; Chosrowjan, H.*; 染川 智弘*; 八ッ橋 知幸*

Chemical Physics Letters, 802, p.139759_1 - 139759_6, 2022/09

 被引用回数:0 パーセンタイル:0.01(Chemistry, Physical)



Electrical properties and energy band alignment of SiO$$_{2}$$/GaN metal-oxide-semiconductor structures fabricated on N-polar GaN(000$$bar{1}$$) substrates

溝端 秀聡*; 冨ヶ原 一樹*; 野崎 幹人*; 小林 拓真*; 吉越 章隆; 細井 卓治*; 志村 考功*; 渡部 平司*

Applied Physics Letters, 121(6), p.062104_1 - 062104_6, 2022/08

N極性GaN(000$$bar{1}$$)基板上に作製したSiO$$_{2}$$/GaN MOS構造の界面特性とエネルギーバンドアライメントを、電気測定と放射光X線光電子分光法を用いて調べた。さらに、得られた結果をGa極性GaN(0001)上のSiO$$_{2}$$/GaN MOS構造の特性と比較した。SiO$$_{2}$$/GaN(000$$bar{1}$$)構造はGaN(0001)基板上に作製した構造よりも熱的に不安定であることがわかった。しかし、絶縁膜堆積後アニールの条件を最適化することにより、SiO$$_{2}$$/GaN(000$$bar{1}$$)構造でも優れた電気特性が得られた。一方で、SiO$$_{2}$$/GaN(000$$bar{1}$$)構造の伝導帯オフセットがSiO$$_{2}$$/GaN(0001)構造よりも小さく、これによるゲートリーク電流の増大が見られた。以上のことから、MOSデバイスの作製においてN極性GaN(000$$bar{1}$$)基板の利用には注意を要することを明らかにした。


Temperature dependence of positron annihilation lifetime in near-surface and bulk of room-temperature ionic liquid observed by a slow positron beam

平出 哲也; 満汐 孝治*; 小林 慶規*; 大島 永康*

Chemical Physics Letters, 795, p.139507_1 - 139507_4, 2022/05

 被引用回数:0 パーセンタイル:0.01(Chemistry, Physical)

N,N,N-Trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI)中において三重項ポジトロニウム(オルトーPs)消滅寿命の温度依存性を、産業技術総合研究所に整備されている垂直型陽電子ビームを用いて150$$^{circ}$$Cまで測定した。TMPA-TFSI液体試料表面から表面近傍とバルク中での測定を行うために、2keVと12keVのエネルギーで陽電子を入射した。融点よりも130$$^{circ}$$C高い150$$^{circ}$$Cにおいても表面の構造による違いが見られた。また、どちらの入射エネルギーでも高温ほど寿命は短くなった。同様の現象は水中においてのみ、オルトーPsと放射線分解生成物であるOHラジカルなどとの反応によって見出されていた。TMPA-TFSIにおける温度依存性においても、オルトーPsの化学反応の存在を示していると考えられた。


Observation of domain structure in non-collinear antiferromagnetic Mn$$_3$$Sn thin films by magneto-optical Kerr effect

内村 友宏*; Yoon, J.-Y.*; 佐藤 佑磨*; 竹内 祐太郎*; 金井 駿*; 武智 涼太*; 岸 桂輔*; 山根 結太*; DuttaGupta, S.*; 家田 淳一; et al.

Applied Physics Letters, 120(17), p.172405_1 - 172405_5, 2022/04

 被引用回数:7 パーセンタイル:91.96(Physics, Applied)

We perform a hysteresis-loop measurement and domain imaging for $$(1100)$$-oriented $$D0_{19}$$-Mn$$_{3+x}$$Sn$$_{1-x}$$ $$(-0.11 le x le 0.14)$$ thin films using magneto-optical Kerr effect (MOKE) and compare it with the anomalous Hall effect (AHE) measurement. We obtain a large Kerr rotation angle of 10 mdeg., comparable with bulk single-crystal Mn$$_3$$Sn. The composition $$x$$ dependence of AHE and MOKE shows a similar trend, suggesting the same origin, i.e., the non-vanishing Berry curvature in the momentum space. Magnetic domain observation at the saturated state shows that x dependence of AHE and MOKE is explained by an amount of reversible area that crucially depends on the crystalline structure of the film. Furthermore, in-depth observation of the reversal process reveals that the reversal starts with nucleation of sub-micrometer-scale domains dispersed in the film, followed by a domain expansion, where the domain wall preferentially propagates along the $$[11bar{2}0]$$ direction. Our study provides a basic understanding of the spatial evolution of the reversal of chiral-spin structure in non-collinear antiferromagnetic thin films.


Fabrication of (Bi$$_2$$)$$_m$$(Bi$$_2$$Te$$_3$$)$$_n$$ superlattice films by Te desorption from a pristine Bi$$_2$$Te$$_3$$ film

日下 翔太郎*; 佐々木 泰祐*; 角田 一樹; 一ノ倉 聖*; 出田 真一郎*; 田中 清尚*; 宝野 和博*; 平原 徹*

Applied Physics Letters, 120(17), p.173102_1 - 173102_5, 2022/04

 被引用回数:1 パーセンタイル:44.44(Physics, Applied)

We fabricated superlattice films composed of Bi$$_2$$ bilayers (BLs) and Bi$$_2$$Te$$_3$$ quintuple layers (QLs) by annealing pure Bi$$_2$$Te$$_3$$ films. It was found that Te desorbs from the QL to form the BL with an activation energy of 2.7 eV. Eventually two distinct stoichiometric phases were formed, Bi$$_1$$Te$$_1$$ (QL-BL-QL) and Bi$$_4$$Te$$_3$$ (QL-BL), as evidenced by scanning transmission emission microscopy measurements. The surface-state dispersion was measured with angle-resolved photoemission spectroscopy and the topological nature of each sample is discussed. Our method offers a convenient and simple way to fabricate superlattice films with different topological properties.


Determination of site occupancy of boron in 6H-SiC by multiple-wavelength neutron holography

林 好一*; Lederer, M.*; 福本 陽平*; 後藤 雅司*; 山本 裕太*; 八方 直久*; 原田 正英; 稲村 泰弘; 及川 健一; 大山 研司*; et al.

Applied Physics Letters, 120(13), p.132101_1 - 132101_6, 2022/03

 被引用回数:0 パーセンタイル:0(Physics, Applied)

The local structure around boron doped in a 6H-type silicon carbide (SiC) was investigated using neutron holography. Three dimensional atomic images reconstructed from multiple-wavelength holograms revealed the boron substitution for both silicon and carbon. To determine the boron locations accurately, we calculated holograms with varying occupancies of six different sites and fitted the image intensities with those obtained from the experimental holograms by the steepest descent method. As a result, it was found that boron atoms were selectively located at the Si-C-cubic site layer. Furthermore, boundaries right above the boron locations were suggested from the absence of atomic images in the upper region of the reconstruction.


Hydration structures of barium ions; ${it Ab initio}$ molecular dynamics simulations using the SCAN meta-GGA density functional and EXAFS spectroscopy studies

山口 瑛子; 小林 恵太; 高橋 嘉夫*; 町田 昌彦; 奥村 雅彦

Chemical Physics Letters, 780, p.138945_1 - 138945_5, 2021/10

 被引用回数:4 パーセンタイル:53.02(Chemistry, Physical)



Martensitic transformation in CrCoNi medium-entropy alloy at cryogenic temperature

Naeem, M.*; Zhou, H.*; He, H.*; Harjo S.; 川崎 卓郎; Lan, S.*; Wu, Z.*; Zhu, Y.*; Wang, X.-L.*

Applied Physics Letters, 119(13), p.131901_1 - 131901_7, 2021/09

 被引用回数:7 パーセンタイル:72.26(Physics, Applied)

We investigated the in situ deformation behavior of the CrCoNi medium-entropy alloy at a cryogenic temperature of 140 K and compared it with deformation at room temperature. The sample exhibited higher strength and larger ductility at the cryogenic temperature. The CrCoNi alloy remained single-phase face-centered cubic at room temperature, while deformation at 140 K resulted in a martensitic transformation to the hexagonal close-packed structure. The phase transformation, an additional deformation mechanism to stacking faults, twinning, and dis- location slip, resulted in a higher work hardening at cryogenic temperature. The study addresses the structure metastability in the CrCoNi alloy, which led to the formation of epsilon-martensite from the intrinsic stacking faults.


Evaluation of edge domains in giant magnetoresistive junctions

Frost, W.*; 関 剛斎*; 窪田 崇秀*; Ramos, R.*; 齊藤 英治; 高梨 弘毅*; 廣畑 貴文*

Applied Physics Letters, 118(17), p.172405_1 - 172405_5, 2021/04

 被引用回数:1 パーセンタイル:14.03(Physics, Applied)

We demonstrate that the spin-Seebeck effect can be used to estimate the volume of edge domains formed in a giant magnetoresistive (GMR) device. The thermal gradient induced by Joule heating can be harnessed by the addition of a ferromagnetically insulating channel of Fe$$_2$$O$$_3$$ on the sides of the GMR pillar. This generates a spin wave in Fe$$_2$$O$$_3$$, which couples with the free-layer edge magnetization and controls the reversal of the ferromagnetic layers in one direction only, increasing the current density from $$(1.1pm0.1)times10^7$$ A/cm$$^2$$ to $$(7.0pm0.5)times10^7$$ A/cm$$^2$$. By simple assumption, we estimate the effect of the edge domain on magnetization reversal to be $$10%-15%$$ by spin-transfer torque.


Observation of quantum interference conductance fluctuations in metal rings with strong spin-orbit coupling

Ramos, R.*; 巻内 崇彦*; 吉川 貴史*; 大門 俊介*; 大柳 洸一*; 齊藤 英治

Applied Physics Letters, 117(24), p.242402_1 - 242402_5, 2020/12

 被引用回数:1 パーセンタイル:7.62(Physics, Applied)

We investigated the magnetotransport properties of mesoscopic platinum nanostructures (wires and rings) with sub-100 nm lateral dimensions at very low temperatures. Despite the strong spin-orbit interaction in platinum, oscillation of the conductance as a function of the external magnetic field due to quantum interference effects was found to appear. The oscillation was decomposed into Aharonov-Bohm periodic oscillations and aperiodic fluctuations of the conductance due to a magnetic flux piercing the loop of the ring and the metal wires forming the nanostructures, respectively. We also investigated the magnetotransport under different bias currents to explore the interplay between electron phase coherence and spin accumulation effects in strong spin-orbit conductors.


Concurrent magneto-optical imaging and magneto-transport readout of electrical switching of insulating antiferromagnetic thin films

Schreiber, F.*; Baldrati, L.*; Schmitt, C.*; Ramos, R.*; 齊藤 英治; Lebrun, R.*; Kl$"a$ui, M.*

Applied Physics Letters, 117(8), p.082401_1 - 082401_5, 2020/08

 被引用回数:20 パーセンタイル:84.19(Physics, Applied)

We demonstrate stable and reversible current induced switching of large-area ($$>$$100 $$mu$$m$$^2$$) antiferromagnetic domains in NiO/Pt by performing concurrent transport and magneto-optical imaging measurements in an adapted Kerr microscope. By correlating the magnetic images of the antiferromagnetic domain changes and magneto-transport signal response in these current-induced switching experiments, we disentangle magnetic and non-magnetic contributions to the transport signal. Our table-top approach establishes a robust procedure to subtract the non-magnetic contributions in the transport signal and extract the spin-Hall magnetoresistance response associated with the switching of the antiferromagnetic domains, enabling one to deduce details of the antiferromagnetic switching from simple transport measurements.


An Electron-capture efficiency in femtosecond filamentation

中島 信昭*; 八ッ橋 知幸*; 迫田 憲治*; 岩倉 いずみ*; 橋本 征奈*; 横山 啓一; 松田 晶平

Chemical Physics Letters, 752, p.137570_1 - 137570_5, 2020/08

 被引用回数:1 パーセンタイル:6.75(Chemistry, Physical)



Understanding water-mediated DNA damage production by molecular dynamics calculation of solvent accessibility

米谷 佳晃*; 中川 洋

Chemical Physics Letters, 749, p.137441_1 - 137441_5, 2020/06

 被引用回数:0 パーセンタイル:0.01(Chemistry, Physical)



Electric field effect on the magnetic domain wall creep velocity in Pt/Co/Pd structures with different Co thicknesses

小山 知弘*; 家田 淳一; 千葉 大地*

Applied Physics Letters, 116(9), p.092405_1 - 092405_5, 2020/03


 被引用回数:3 パーセンタイル:25.71(Physics, Applied)

The electric field (EF) modulation of magnetic domain wall (DW) creep velocity $$v$$ in Pt/Co/Pd structure with perpendicular magnetic anisotropy (MA) has been studied. The structures with different Co thickness $$t_mathrm{Co}$$ up to $$sim 1$$ nm are investigated. In all samples, applying a gate voltage induces a clear change in $$v$$. Thicker samples provide a higher $$v$$ modulation efficiency, and the $$v$$ modulation magnitude of more than a factor of 100 times is observed in the thickest $$t_mathrm{Co}$$ of 0.98 nm. The parameter characterizing the creep motion is significantly affected by the EF, resulting in the modulation of $$v$$. Unlike the $$v$$ case, the MA modulation efficiency decreases with increasing $$t_mathrm{Co}$$. The present results are discussed based on the EF-induced change in the interfacial Dzyaloshinskii-Moriya interaction (iDMI), which has been recently demonstrated in the same structure, and $$t_mathrm{Co}$$ dependence of the DW energy. The $$t_mathrm{Co}$$ dependence of the $$v$$ modulation suggests that the EF effect on the iDMI is more important than the MA.


Absence of evidence of spin transport through amorphous Y$$_3$$Fe$$_5$$O$$_{12}$$

Gomez-Perez, J. M.*; 大柳 洸一*; 八尋 黎明*; Ramos, R.*; Hueso, L. E.*; 齊藤 英治; Casanova, F.*

Applied Physics Letters, 116(3), p.032401_1 - 032401_5, 2020/01

 被引用回数:8 パーセンタイル:58.46(Physics, Applied)

We probe the current-induced magnetic switching of insulating antiferromagnet-heavy-metal systems, by electrical spin Hall magnetoresistance measurements and direct imaging, identifying a reversal occurring by domain wall (DW) motion. We observe switching of more than one-third of the antiferromagnetic domains by the application of current pulses. Our data reveal two different magnetic switching mechanisms leading together to an efficient switching, namely, the spin-current induced effective magnetic anisotropy variation and the action of the spin torque on the DWs.


Polaronic nature of a muonium-related paramagnetic center in SrTiO$$_3$$

伊藤 孝; 髭本 亘; 幸田 章宏*; 下村 浩一郎*

Applied Physics Letters, 115(19), p.192103_1 - 192103_4, 2019/11

 被引用回数:7 パーセンタイル:38.26(Physics, Applied)

The hyperfine features and thermal stability of a muonium (Mu)-related paramagnetic center were investigated in the SrTiO$$_3$$ perovskite titanate via muon spin rotation spectroscopy. The hyperfine coupling tensor of the paramagnetic center was found to have prominent dipolar characteristics, indicating that the electron spin density is dominantly distributed on a Ti site to form a small polaron near an ionized Mu$$^+$$ donor. Based on a hydrogen-Mu analogy, interstitial hydrogen is also expected to form such a polaronic center in the dilute doping limit. The small activation energy of 30(3) meV found for the thermal dissociation of the Mu$$^+$$-polaron complex suggests that the strain energy required to distort the lattice is comparable to the electronic energy gained by localizing the electron.

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