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論文

Laser-induced creation of antiferromagnetic 180-degree domains in NiO/Pt bilayers

Meer, H.*; Wust, S.*; Schmitt, C.*; Herrgen, P.*; Fuhrmann, F.*; Hirtle, S.*; Bednarz, B.*; Rajan, A.*; Ramos, R.*; Nio, M. A.*; et al.

Advanced Functional Materials, 33(21), p.2213536_1 - 2213536_6, 2023/05

https://doi.org/10.1002/adfm.202213536

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 $^{circ}$ domain walls and domains with 180 $^{circ}$ different Nel 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.

論文

Magnetic sensitivity distribution of Hall devices in antiferromagnetic switching experiments

Schreiber, F.*; Meer, H.*; Schmitt, C.*; Ramos, R.*; 齊藤英治; Baldrati, L.*; Klui, M.*

Physical Review Applied (Internet), 16(6), p.064023_1 - 064023_9, 2021/12

https://doi.org/10.1103/PhysRevApplied.16.064023

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.

論文

Experimental evidence for common driving effects in low-energy fission from sublead to actinides

Schmitt, C.*; Lemasson, A.*; Schmidt, K.-H.*; Jhingan, A.*; Biswas, S.*; Kim, Y. H.*; Ramos, D.*; Andreyev, A. N.; Curien, D.*; Ciemala, M.*; et al.

Physical Review Letters, 126(13), p.132502_1 - 132502_6, 2021/04

https://doi.org/10.1103/PhysRevLett.126.132502

被引用回数：15 パーセンタイル：84.11(Physics, Multidisciplinary)

Isotopic distributions of fragments from fission of the neutron-deficient $^{178}$ Hg nuclide are reported. This experimental observable is obtained for the first time in the region around lead using an innovative approach based on inverse kinematics and the coincidence between the large acceptance magnetic spectrometer VAMOS++ and a new detection arm close to the target. The average fragment ratio and prompt neutron multiplicity are derived and compared with current knowledge from actinide fission. A striking consistency emerges, revealing the unexpected dominant role of the proton subsystem with atomic number between the = 28 and 50 magic numbers. The origin of nuclear charge polarization in fission and fragment deformation at scission are discussed.

論文

Direct imaging of current-induced antiferromagnetic switching revealing a pure thermomagnetoelastic switching mechanism in NiO

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

https://doi.org/10.1021/acs.nanolett.0c03367

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.

論文

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.*; Klui, M.*

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

https://doi.org/10.1063/5.0011852

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.

論文

Efficient spin torques in antiferromagnetic CoO/Pt quantified by comparing field- and current-induced switching

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

https://doi.org/10.1103/PhysRevLett.125.077201

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 $4times10^{-11}$ TA $^{-1}$ m. The Nel vector final state is in line with a thermomagnetoelastic switching mechanism for a negative magnetoelastic constant of the CoO.

論文

$^{239}$ Pu nuclear magnetic resonance in the candidate topological insulator PuB

Dioguardi, A. P.*; 安岡弘志*; Thomas, S. M.*; 酒井宏典; Cary, S. K.*; Kozimor, S. A.*; Albrecht-Schmitt, T. E.*; Choi, H. C.*; Zhu, J.-X.*; Thompson, J. D.*; et al.

Physical Review B, 99(3), p.035104_1 - 035104_6, 2019/01

https://doi.org/10.1103/PhysRevB.99.035104

被引用回数：8 パーセンタイル：37.59(Materials Science, Multidisciplinary)

正方晶プルトニウムボロン化合物PuB $_{4}$ の単結晶、および粉末試料を用いて、 $^{239}$ Pu核核磁気共鳴(NMR)実験を行なった。この化合物は、最近になって強相関電子系のトポロジカル絶縁体候補物質と考えられている。 $^{239}$ Pu核NMRスペクトルは、結晶内Pu位置の局所対称性を反映したものとなっており、NMRシフトとNMR緩和率の温度依存性は、エネルギーギャップをもつ非磁性状態にあることが示唆された。これは、密度汎関数理論計算結果とも矛盾しない。実際に観測された巨視的なギャップ状態は、本化合物がトポロジカル絶縁体候補であることを支持している。

論文

Neutron-hole states in $^{131}$ Sn and spin-orbit splitting in neutron-rich nuclei

Orlandi, R.; Pain, S. D.*; Ahn, S.*; Jungclaus, A.*; Schmitt, K. T.*; Bardayan, D. W.*; Catford, W. N.*; Chapman, R.*; Chipps, K. A.*; Cizewski, J. A.*; et al.

Physics Letters B, 785, p.615 - 620, 2018/10

https://doi.org/10.1016/j.physletb.2018.08.005

被引用回数：7 パーセンタイル：53.6(Astronomy & Astrophysics)

Low-lying neutron-hole states in $^{131}$ Sn were populated via the $^{132}$ Sn(d,t) reaction at Oak Ridge National Laboratory. The triton angular distributions were compared to DWBA calculations and revealed spectroscopic factors compatible with a single-hole nature of the states populated. The data permit to determine the spin-orbit splitting of the strongly bound $d_{3/2}$ and $d_{5/2}$ neutron orbits below the shell gap, which was compared to the splitting of the weakly bound 3 and 2 orbits above the gap. The comparison revealed a smaller energy splitting of the 3 orbits. All splittings were reproduced using Woods-Saxon calculations, and the lower splitting of the 3 orbits was explained to arise from the large radial extent of the wavefunction and small value of the amplitude at the surface. This result is important to understand at a fundamental level the spin-orbit interaction, and its effects on neutron-rich nuclei.

口頭

Neutron hole states in $^{131}$ Sn studied via the $^{132}$ Sn(d,t) $^{131}$ Sn reaction

Orlandi, R.; Pain, S. D.*; Bardayan, D. W.*; Gross, C. J.*; Smith, M. S.*; Jungclaus, A.*; Ahn, S.*; Jones, K. L.*; Pittman, S. T.*; Schmitt, K. T.*; et al.

no journal, ,

Knowledge of single-particle energies in the vicinity of exotic doubly-magic nuclei is of critical importance to understand evolution of nuclear structure. In the present work, the $^{132}$ Sn(d,t) $^{131}$ Sn reaction (Q=-1.055 MeV) was studied in inverse kinematics at HRIBF of Oak Ridge National Laboratory. The $^{132}$ Sn ISOL beam was post-accelerated to an energy of 4.39 MeV/u using the ORNL HRIBF accelerator. The beam (average intensity of 1.2e4 pps) impinged on a 250 g/cm $^{2}$ deuterated polyethylene target, for approximately 4 days. Ejected tritons were detected using the Super ORRUBA array of segmented Si telescopes. Low-lying states in $^{131}$ Sn were populated in the experiment. Preliminary results will be shown.

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