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Meer, H.*; Wust, S.*; Schmitt, C.*; Herrgen, P.*; Fuhrmann, F.*; Hirtle, S.*; Bednarz, B.*; Rajan, A.*; Ramos, R.*; Ni
o, M. A.*; et al.
Advanced Functional Materials, 33(21), p.2213536_1 - 2213536_6, 2023/05
被引用回数：0 パーセンタイル：54.89(Chemistry, Multidisciplinary)The antiferromagnetic order in heterostructures of NiO/Pt thin films can be modified by optical pulses. After the irradiation with laser light, the optically induced creation of antiferromagnetic domains can be observed by imaging the created domain structure utilizing the X-ray magnetic linear dichroism effect. The effect of different laser polarizations on the domain formation can be studied and used to identify a polarization-independent creation of 180
domain walls and domains with 180 different N
el vector orientation. By varying the irradiation parameters, the switching mechanism can be determined to be thermally induced. This study demonstrates experimentally the possibility to optically create antiferromagnetic domains, an important step towards future functionalization of all optical switching mechanisms in antiferromagnets.
Zhou, Z.*; Frost, W.*; Lloyd, D. C.*; 関 剛斎*; 窪田 崇秀*; Ramos, R.*; 齊藤 英治; 高梨 弘毅; 廣畑 貴文*
Journal of Magnetism and Magnetic Materials, 571, p.170575_1 - 170575_5, 2023/04
被引用回数：0 パーセンタイル：0(Materials Science, Multidisciplinary)Recent development in neuromorphic computation allows us to achieve low power and highly efficient calculations better than the conventional von Neumann computation. In order to achieve realistic synaptic operation, potentiation to add weighting to strengthen a selected artificial synapse. Such functionality can be achieved by reducing the electrical resistance of the artificial synapse. Recently, a ferromagnetic Heusler alloy used in a magnetoresistive junction has been demonstrated to crystallise via the layer-by-layer mode by introducing an electrical current pulse. In this study, we have extended the current-induced crystallisation to a junction with epitaxially-grown Heusler alloy after post-annealing for crystallisation. By combining this potentiation functionality with the neuromorphic operation, realistic synaptic computation can be developed.
Schreiber, F.*; Meer, H.*; Schmitt, C.*; Ramos, R.*; 齊藤 英治; Baldrati, L.*; Kl
ui, M.*
Physical Review Applied (Internet), 16(6), p.064023_1 - 064023_9, 2021/12
被引用回数：3 パーセンタイル：27.71(Physics, Applied)We analyze the complex impact of the local magnetic spin texture on the transverse Hall-type voltage in device structures utilized to measure magnetoresistance effects. We find a highly localized and asymmetric magnetic sensitivity in the eight-terminal geometries that are frequently used in current-induced switching experiments, for instance, to probe antiferromagnetic materials. Using current-induced switching of antiferromagnetic NiO/Pt as an example, we estimate the change in the spin Hall magnetoresistance signal associated with switching events based on the domain-switching patterns observed via direct imaging. This estimate correlates with the actual electrical data after subtraction of a nonmagnetic contribution. Here, the consistency of the correlation across three measurement geometries with fundamentally different switching patterns strongly indicates a magnetic origin of the measured and analyzed electrical signals.
Cl isotopesLinh, B. D.*; Corsi, A.*; Gillibert, A.*; Obertelli, A.*; Doornenbal, P.*; Barbieri, C.*; Chen, S.*; Chung, L. X.*; Duguet, T.*; G
mez-Ramos, M.*; et al.
Physical Review C, 104(4), p.044331_1 - 044331_16, 2021/10
被引用回数：5 パーセンタイル：46.8(Physics, Nuclear)理化学研究所のRIビームファクトリーにて中性子過剰Clの励起状態を
Arからのノックアウト反応によって生成し、脱励起ガンマ線からそのエネルギー準位を測定した。また、陽子ノックアウトの運動量分布から
Clの基底状態が
であることがわかった。その結果を大規模殻模型計算およびいくつかの第一原理計算と比較した。Cl同位体の基底状態および第一励起状態は、計算で用いた相互作用に敏感であることがわかった。それは、陽子の一粒子エネルギーと四重極集団運動との複雑な結合によるためであると考えられる。
吉川 貴史*; Reitz, D.*; 伊藤 宏陽*; 巻内 崇彦*; 杉本 宜陽*; 恒川 翔*; 大門 俊介*; 大柳 洸一*; Ramos, R.*; 高橋 三郎*; et al.
Nature Communications (Internet), 12, p.4356_1 - 4356_7, 2021/07
被引用回数：19 パーセンタイル：88.38(Multidisciplinary Sciences)Thermoelectric effects have been applied to power generators and temperature sensors that convert waste heat into electricity. The effects, however, have been limited to electrons to occur, and inevitably disappear at low temperatures due to electronic entropy quenching. Here, we report thermoelectric generation caused by nuclear spins in a solid: nuclear-spin Seebeck effect. The sample is a magnetically ordered material MnCO
having a large nuclear spin 
of 
Mn nuclei and strong hyperfine coupling, with a Pt contact. In the system, we observe low-temperature thermoelectric signals down to 100 mK due to nuclear-spin excitation. Our theoretical calculation in which interfacial Korringa process is taken into consideration quantitatively reproduces the results. The nuclear thermoelectric effect demonstrated here offers a way for exploring thermoelectric science and technologies at ultralow temperatures.
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：7.86(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
O on the sides of the GMR pillar. This generates a spin wave in FeO, 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 
A/cm
to 
A/cm. By simple assumption, we estimate the effect of the edge domain on magnetization reversal to be 
by spin-transfer torque.
Meer, H.*; Schreiber, F.*; Schmitt, C.*; Ramos, R.*; 齊藤 英治; Gomonay, O.*; Sinova, J.*; Baldrati, L.*; Klui, M.*
Nano Letters, 21(1), p.114 - 119, 2021/01
被引用回数：51 パーセンタイル：96.99(Chemistry, Multidisciplinary)We unravel the origin of current-induced magnetic switching of insulating antiferromagnet/heavy metal systems. We utilize concurrent transport and magneto-optical measurements to image the switching of antiferromagnetic domains in specially engineered devices of NiO/Pt bilayers. Different electrical pulsing and device geometries reveal different final states of the switching with respect to the current direction. We can explain these through simulations of the temperature-induced strain, and we identify the thermomagnetoelastic switching mechanism combined with thermal excitations as the origin, in which the final state is defined by the strain distributions and heat is required to switch the antiferromagnetic domains. We show that such a potentially very versatile noncontact mechanism can explain the previously reported contradicting observations of the switching final state, which were attributed to spin-orbit torque mechanisms.
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：5.55(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.
Prez S
nchez, R.*; Jurado, B.*; Mot, V.*; Roig, O.*; Dupuis, M.*; Bouland, O.*; Denis-Petit, D.*; Marini, P.*; Mathieu, L.*; Tsekhanovich, I.*; et al.
Physical Review Letters, 125(12), p.122502_1 - 122502_5, 2020/09
被引用回数：13 パーセンタイル：70.32(Physics, Multidisciplinary)Reliable neutron-induced-reaction cross sections of unstable nuclei are essential for nuclear astrophysics and applications but their direct measurement is often impossible. The surrogate-reaction method is one of the most promising alternatives to access these cross sections. In this work, we successfully applied the surrogate-reaction method to infer for the first time both the neutron-induced fission and radiative capture cross sections of 
Pu in a consistent manner from a single measurement. This was achieved by combining simultaneously measured fission and 
-emission probabilities for the 
Pu(
He, He') surrogate reaction with a calculation of the angular-momentum and parity distributions populated in this reaction. While other experiments measure the probabilities for some selected -ray transitions, we measure the -emission probability. This enlarges the applicability of the surrogate-reaction method.
Schreiber, F.*; Baldrati, L.*; Schmitt, C.*; Ramos, R.*; 齊藤 英治; Lebrun, R.*; Klui, M.*
Applied Physics Letters, 117(8), p.082401_1 - 082401_5, 2020/08
被引用回数：25 パーセンタイル：84.2(Physics, Applied)We demonstrate stable and reversible current induced switching of large-area (
100 
m) 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.
Baldrati, L.*; Schmitt, C.*; Gomonay, O.*; Lebrun, R.*; Ramos, R.*; 齊藤 英治; Sinova, J.*; Klui, M.*
Physical Review Letters, 125(7), p.077201_1 - 077201_6, 2020/08
被引用回数：36 パーセンタイル：91.79(Physics, Multidisciplinary)We achieve current-induced switching in collinear insulating antiferromagnetic CoO/Pt, with fourfold in-plane magnetic anisotropy. This is measured electrically by spin Hall magnetoresistance and confirmed by the magnetic field-induced spin-flop transition of the CoO layer. By applying current pulses and magnetic fields, we quantify the efficiency of the acting current-induced torques and estimate a current-field equivalence ratio of 
TA
m. The N
el vector final state 
is in line with a thermomagnetoelastic switching mechanism for a negative magnetoelastic constant of the CoO.
) two-proton knockout from neutron-rich nucleiFrotscher, A.*; Gmez-Ramos, M.*; Obertelli, A.*; Doornenbal, P.*; Authelet, G.*; 馬場 秀忠*; Orlandi, R.; 他86名*
Physical Review Letters, 125(1), p.012501_1 - 012501_7, 2020/07
被引用回数：5 パーセンタイル：38.78(Physics, Multidisciplinary)Twenty-one two-proton () knock-out cross sections of neutron-rich radioactive isotopes were measured in inverse kinematics using the MINOS time-projection chamber at RIBF, RIKEN. The proton angular distributions, measured for the first time, reveal that the reaction kinematics of the () reaction is consistent with sequential proton collisions within the projectile nucleus.
Fe
O
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：9 パーセンタイル：53.43(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.
Chrysalidis, K.*; Barzakh, A. E.*; Ahmed, R.*; Andreyev, A. N.; Ballof, J.*; Cubiss, J. G.*; Fedorov, D. V.*; Fedosseev, V. N.*; Fraile, L. M.*; Harding, R. D.*; et al.
Nuclear Instruments and Methods in Physics Research B, 463, p.472 - 475, 2020/01
被引用回数：3 パーセンタイル：36.4(Instruments & Instrumentation)放射壊変によって生成された多数のジスプロシウム同位体について、ISOLDEのレーザー共鳴イオン源(RILIS)を用いてイオン源内レーザー分光法によって研究した。
Dyに対する相対的な同位体シフトを
(gs) 
共鳴遷移を用いて測定した。電子的因子Fとマスシフト因子Mを導出し、それらを使って
Dyと
Dyの平均自乗荷電半径の変化を初めて決定した。
八尋 黎明*; 吉川 貴史*; Ramos, R.*; 大柳 洸一*; 日置 友智*; 大門 俊介*; 齊藤 英治
Physical Review B, 101(2), p.024407_1 - 024407_7, 2020/01
被引用回数：19 パーセンタイル：77.9(Materials Science, Multidisciplinary)We report the observation of anomalous peak structures induced by hybridized magnon-phonon excitation (magnon polarons) in the magnetic field dependence of the spin Peltier effect (SPE) in a LuBi
Fe
GaO (BiGa:LuIG) with Pt contact. The SPE peaks coincide with magnetic fields tuned to the threshold of magnonpolaron formation, consistent with the previous observation in the spin Seebeck effect. The enhancement of SPE is attributed to the lifetime increase in spin current caused by magnon-phonon hybridization in BiGa:LuIG.
Ramos, R.*; 日置 友智*; 橋本 佑介*; 吉川 貴史*; Frey, P.*; Kreil, A. J. E.*; Vasyuchka, V. I.*; Serga, A. A.*; Hillebrands, B.*; 齊藤 英治
Nature Communications (Internet), 10, p.5162_1 - 5162_8, 2019/11
被引用回数：23 パーセンタイル：76.88(Multidisciplinary Sciences)Resonant enhancement of spin Seebeck effect (SSE) due to phonons was recently discovered in YFeO (YIG). This effect is explained by hybridization between the magnon and phonon dispersions. However, this effect was observed at low temperatures and high magnetic fields, limiting the scope for applications. Here we report observation of phonon-resonant enhancement of SSE at room temperature and low magnetic field. We observe in LuBiFeGaO an enhancement 700% greater than that in a YIG film and at very low magnetic fields around 10 T, almost one order of magnitude lower than that of YIG. The result can be explained by the change in the magnon dispersion induced by magnetic compensation due to the presence of non-magnetic ion substitutions. Our study provides a way to tune the magnon response in a crystal by chemical doping, with potential applications for spintronic devices.
O/Pt/FeO epitaxial trilayers吉川 貴史*; 鈴木 基寛*; Ramos, R.*; Aguirre, M. H.*; 岡林 潤*; 内田 健一*; Lucas, I.*; Anadn, A.*; 菊池 大介*; Algarabel, P. A.*; et al.
Journal of Applied Physics, 126(14), p.143903_1 - 143903_11, 2019/10
被引用回数：10 パーセンタイル：49.82(Physics, Applied)Induced Pt ferromagnetism in FeO/Pt/FeO epitaxial trilayer films has been investigated by means of X-ray magnetic circular dichroism (XMCD) at the Pt 
-edges at various temperatures from 300 K to 12 K, including the metal-insulator transition temperature of FeO (
K). At all the temperatures, we observed clear XMCD signals due to Pt ferromagnetism, the amplitude of which was determined to be 0.39 
at 300K and 0.52 at 12 K for the sample with the Pt thickness of 
nm. Interestingly, these values are comparable to or even greater than those in Pt/3
-ferromagnetic-metal (Fe, Ni, Co, and Ni
Fe
) junction systems. The results can be interpreted in terms of a possible Fe interdiffusion into the Pt layer and also possible Fe-Pt alloying due to its high-temperature deposition.
el order switching in antiferromagnetic thin films revealed by magnetotransport and direct imagingBaldrati, L.*; Gomonay, O.*; Ross, A.*; Filianina, M.*; Lebrun, R.*; Ramos, R.*; Leveille, C.*; Fuhrmann, F.*; Forrest, T. R.*; Maccherozzi, F.*; et al.
Physical Review Letters, 123(17), p.177201_1 - 177201_6, 2019/10
被引用回数：118 パーセンタイル：98.44(Physics, Multidisciplinary)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.
Hg, 
Hg, 
Hg and 
HgWrzosek-Lipska, K.*; Rezynkina, K.*; Bree, N.*; Zieli
ska, M.*; Gaffney, L. P.*; Petts, A.*; Andreyev, A. N.; Bastin, B.*; Bender, M.*; Blazhev, A.*; et al.
European Physical Journal A, 55(8), p.130_1 - 130_23, 2019/08
被引用回数：11 パーセンタイル：74.44(Physics, Nuclear)The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 
Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of 0
, 2, and 4
states was observed in all nuclei under study. Reduced 
matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions.
-FeO/NiO/Pt epitaxial stacksDong, B.-W.*; Baldrati, L.*; Schneider, C.*; 新関 友彦*; Ramos, R.*; Ross, A.*; Cramer, J.*; 齊藤 英治; Klui, M.*
Applied Physics Letters, 114(10), p.102405_1 - 102405_5, 2019/03
被引用回数：11 パーセンタイル：49.82(Physics, Applied)We study the spin Hall magnetoresistance (SMR) in epitaxial -FeO/NiO(001)/Pt stacks, as a function of temperature and thickness of the antiferromagnetic insulating NiO layer. Upon increasing the thickness of NiO from 0 nm to 10 nm, we detect a sign change of the SMR in the temperature range between 10 K and 280 K. This temperature dependence of the SMR in our stacks is different compared to that of previously studied yttrium iron garnet/NiO/Pt, as we do not find any peak or sign change as a function of temperature. We explain our data by a combination of spin current reflection from both the NiO/Pt and -FeO/NiO interfaces and the thickness-dependent exchange coupling mode between the NiO and -FeO layers, comprising parallel alignment for thin NiO and perpendicular alignment for thick NiO.
