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Journal Articles

Magnetic hysteresis induction with nanocolumnar defects in magnetic insulators

Harii, Kazuya*; Umeda, Maki; Arisawa, Hiroki*; Hioki, Tomosato*; Sato, Nana; Okayasu, Satoru; Ieda, Junichi

Journal of the Physical Society of Japan, 92(7), p.073701_1 - 073701_4, 2023/07

 Times Cited Count:0 Percentile:69.97(Physics, Multidisciplinary)

Journal Articles

The Damage analysis for irradiation tolerant spin-driven thermoelectric device based on single-crystalline Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt heterostructures

Ieda, Junichi; Okayasu, Satoru; Harii, Kazuya*; Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Ishida, Masahiko*; Saito, Eiji

IEEE Transactions on Magnetics, 58(8), p.1301106_1 - 1301106_6, 2022/08

 Times Cited Count:1 Percentile:26.34(Engineering, Electrical & Electronic)

The combination of spin-driven thermoelectric (STE) devices based on spin Seebeck effect (SSE), and radioactive isotopes as heat sources, has potential as a next-generation method of power generation in applications such as power supplies for space probes. However, there has been very limited knowledge available indicating the irradiation tolerance of spin thermoelectric devices. Through analysis using a heavy ion-beam accelerator and the hard X-ray photoemission spectroscopy (HAXPES) measurements, we show that a prototypical STE device based on Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt heterostructures has tolerance to irradiation of high-energy heavy-ion beams. We used 320 MeV gold ion beams modeling cumulative damages due to fission products emitted from the surface of spent nuclear fuels. By varying the dose level, we confirmed that the thermoelectric and magnetic properties of the SSE elements are not affected by the ion-irradiation dose up to $$10^{10}$$ ions/cm$$^2$$ fluence and that the SSE signal is extinguished around $$10^{12}$$ ions/cm$$^2$$, in which the ion tracks almost fully cover the sample surface. In addition, the HAXPES measurements were performed to understand the effects at the interface of Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt. The HAXPES measurements suggest that the chemical reaction that diminishes the SSE signals is enhanced with the increase of the irradiation dose. We share the current understandings of the damage analysis in Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt for developing better STE devices applicable to harsh environmental usages.

Journal Articles

Tolerance of spin-Seebeck thermoelectricity against irradiation by swift heavy ions

Okayasu, Satoru; Harii, Kazuya*; Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Ishida, Masahiko*; Ieda, Junichi; Saito, Eiji

Journal of Applied Physics, 128(8), p.083902_1 - 083902_7, 2020/08


 Times Cited Count:3 Percentile:20.59(Physics, Applied)

Journal Articles

Hard X-ray photoelectron spectroscopy study of Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$

Kobata, Masaaki; Yoshii, Kenji; Fukuda, Tatsuo; Kawasaki, Ikuto; Okane, Tetsuo; Yamagami, Hiroshi; Yaita, Tsuyoshi; Harii, Kazuya; Ieda, Junichi; Okayasu, Satoru; et al.

JPS Conference Proceedings (Internet), 30, p.011192_1 - 011192_6, 2020/03

High energy X-ray photoelectron spectroscopy (HAXPES) measurements were carried out for the Spin Seebeck system Pt/Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$(YIG). This system was found to show anomalous Hall effect, possible due to the formation of intermetallic compounds between Fe$$^{3+}$$ and Pt. To reveal this possibility, we have measured the Fe 1s photoelectron peaks by using HAXPES. It was found that the Fe ions consist of Fe$$^{3+}$$ in YIG and metallic Fe. The formation of the metallic state is consistent with the proposed origin of the anomalous Hall effect. Other spectra such as Pt 4f will be presented at the conference.

Journal Articles

Spin hydrodynamic generation

Takahashi, Ryo*; Matsuo, Mamoru; Ono, Masao; Harii, Kazuya; Chudo, Hiroyuki; Okayasu, Satoru; Ieda, Junichi; Takahashi, Saburo*; Maekawa, Sadamichi; Saito, Eiji

Nature Physics, 12, p.52 - 56, 2016/01

 Times Cited Count:102 Percentile:96.34(Physics, Multidisciplinary)

Journal Articles

Ion induced modifications of Mn-doped ZnO films

Matsunami, Noriaki*; Ito, M.*; Kato, M.*; Okayasu, Satoru; Sataka, Masao*; Kakiuchida, Hiroshi*

Nuclear Instruments and Methods in Physics Research B, 365(Part A), p.191 - 195, 2015/12

 Times Cited Count:6 Percentile:46.42(Instruments & Instrumentation)

We have studied ion impact effects on atomic structure in terms of X-ray diffraction (XRD), optical absorption and electrical resistivity of Mn (6%)-doped ZnO films under 100 MeV Xe ion impact at room temperature. We find the monotonic reduction of the XRD intensity to 1/50 of that of unirradiated film at 5 $$times$$10$$^{14}$$ cm$$^{-2}$$, little bandgap change ($$<$$0.02 eV) and decrease of the resistivity by 4 order of magnitude. The resistivity modification has been compared with that by irradiations of low energy ions such as 100 keV Ne and N, which show more effective decrease of resistivity. We also find that temperature (T) dependence of the magnetic susceptibility ($$chi$$) of Mn-doped ZnO follows the Curie law: $$chi$$ = $$chi$$$$_{o}$$ + C/T (i.e., paramagnetic) and the Curie constant C decreases to a half of that before irradiation (C$$_{O}$$ = 0.012 emu cm$$^{-3}$$ K) at 100 MeV Xe ion fluence of 10$$^{12}$$ cm$$^{-2}$$.

Journal Articles

Barnett effect in paramagnetic states

Ono, Masao; Chudo, Hiroyuki; Harii, Kazuya; Okayasu, Satoru; Matsuo, Mamoru; Ieda, Junichi; Takahashi, Ryo*; Maekawa, Sadamichi; Saito, Eiji

Physical Review B, 92(17), p.174424_1 - 174424_4, 2015/11

 Times Cited Count:29 Percentile:75.01(Materials Science, Multidisciplinary)

Journal Articles

Equilibrium and non-equilibrium charge-state distributions of 2.0 MeV/u carbon ions passing through carbon foils

Imai, Makoto*; Sataka, Masao*; Matsuda, Makoto; Okayasu, Satoru; Kawatsura, Kiyoshi*; Takahiro, Katsumi*; Komaki, Kenichiro*; Shibata, Hiromi*; Nishio, Katsuhisa

Nuclear Instruments and Methods in Physics Research B, 354, p.172 - 176, 2015/07

 Times Cited Count:14 Percentile:75.98(Instruments & Instrumentation)

Both equilibrium and non-equilibrium charge-state distributions were studied experimentally for 2.0 MeV/u carbon ions after passing through carbon foils. Measured charge-state distribution established the equilibrium at a target thickness of 10 $$mu$$g/cm$$^{2}$$ and this remained unchanged until a maximum target thickness of 98 $$mu$$g/cm$$^{2}$$. The equilibrium charge-state distribution, the equilibrium mean charge-state, and the width and skewness of the equilibrium distribution were compared with predictions using existing semi-empirical formulae as well as simulation results, including the ETACHA code. It was found that charge-state distributions, mean charge states, and distribution widths for C$$^{2+}$$, C$$^{3+}$$, and C$$^{4+}$$ incident ions merged into quasi-equilibrium values at a target thickness of 5.7 $$mu$$g/cm$$^{2}$$ in the pre-equilibrium region and evolved simultaneously to the "real equilibrium" values for all of the initial charge states, including C$$^{5+}$$ and C$$^{6+}$$ ions. Two kinds of simulation, ETACHA and solution of rate equations taking only single electron transfers into account, were used, and both of them reproduced the measured charge evolution qualitatively. The quasi-equilibrium behavior could be reproduced with the ETACHA code, but not with solution of elementary rate equations.

Journal Articles

Line splitting by mechanical rotation in nuclear magnetic resonance

Harii, Kazuya; Chudo, Hiroyuki; Ono, Masao; Matsuo, Mamoru; Ieda, Junichi; Okayasu, Satoru; Maekawa, Sadamichi; Saito, Eiji

Japanese Journal of Applied Physics, 54(5), p.050302_1 - 050302_3, 2015/05

 Times Cited Count:13 Percentile:50.38(Physics, Applied)

Journal Articles

Commensurate and incommensurate vortex states confined in mesoscopic triangles of weak pinning superconducting thin films

Kokubo, Nobuhito*; Miyahara, Hajime*; Okayasu, Satoru; Nojima, Tsutomu*

Journal of the Physical Society of Japan, 84(4), p.043704_1 - 043704_4, 2015/04

 Times Cited Count:4 Percentile:35.18(Physics, Multidisciplinary)

We report on the direct observation of vortex states confined in equilateral and isosceles triangular dots of weak pinning amorphous superconducting thin films with a scanning superconducting quantum interference device microscope. The observed images illustrate not only pieces of a triangular vortex lattice as commensurate vortex states, but also incommensurate vortex states including metastable ones. We comparatively analyze vortex configurations found in different sample geometries and discuss the symmetry and stability of commensurate and incommensurate vortex configurations against deformations of the sample shape.

Journal Articles

Direct imaging of vortex polygons and vortex shells in mesoscopic squares of a weak pinning superconducting thin film

Kokubo, Nobuhito*; Okayasu, Satoru; Nojima, Tsutomu*; Tamochi, Hirotaka*; Shinozaki, Bunju*

Journal of the Physical Society of Japan, 83(8), p.083704_1 - 083704_5, 2014/08

 Times Cited Count:15 Percentile:67.48(Physics, Multidisciplinary)

Journal Articles

Observation of Barnett fields in solids by nuclear magnetic resonance

Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru; Ieda, Junichi; Haruki, Rie*; Okayasu, Satoru; Maekawa, Sadamichi; Yasuoka, Hiroshi; Saito, Eiji

Applied Physics Express, 7(6), p.063004_1 - 063004_4, 2014/06

 Times Cited Count:44 Percentile:84.65(Physics, Applied)

A magnetic field is predicted to emerge on a particle in a rotating body even if the body is electrically neutral. This emergent field is called a Barnett field. We show that nuclear magnetic resonance (NMR) enables direct measurement of the Barnett field in solids. We rotated both a sample and an NMR coil synchronously at high speed and found an NMR shift whose sing reflects that of the nuclear magnetic moments. This result provides direct evidence of the Barnett field. The use of NMR for Barnett field measurement enables the unknown signs of nuclear magnetic moments in solids to be determined.

Journal Articles

Ultracentrifuge experiment on AgI super-ionic conductor

Ono, Masao; Okayasu, Satoru; Iguchi, Yusuke*; Esaka, Fumitaka; Bagum, R.*; Haruki, Rie; Mashimo, Tsutomu*

Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan (Internet), 12(ists29), p.Tq_1 - Tq_3, 2014/04

We had realized the composition gradient of elements or isotopes in some binary alloys or single element by solid-state centrifugation. While, it might difficult to realize graded structure of elements in binary ionic crystal by centrifugation as it strongly keeps their stoichiometry. However, isotope fractionation in binary ionic crystal by centrifugation might be expected as the self-diffusion of ions occurs. We have planed the ultracentrifuge experiments on $$alpha$$-AgI superionic conductor to investigate the isotope effect in binary ionic crystal under a strong centrifugal acceleration field. $$alpha$$-AgI superionic conductor is suitable for the confirmation experiment as it is an intrinsic ionic crystal and Ag ions have high diffusivity. For the first stage, we have experimentally searched the experimental conditions of magnitude of centrifugal acceleration and temperature that ensure the experiment without decomposition. It is confirmed that the combination of experimental conditions of up to 6.1$$times$$10$$^{5}$$ g, 350$$^{circ}$$C, 24h ensure the experiment without decomposition at least.

Journal Articles

Enhancement of critical current densities in (Ba,K)Fe$$_{2}$$As$$_{2}$$ by 320 MeV Au irradiation in single crystals and by high-pressure sintering in powder-in-tube wires

Pyon, S.*; Taen, Toshihiro*; Otake, Fumiaki*; Tsuchiya, Yuji*; Inoue, Hiroshi*; Akiyama, Hiroki*; Kajitani, Hideki; Koizumi, Norikiyo; Okayasu, Satoru; Tamegai, Tsuyoshi*

Applied Physics Express, 6(12), p.123101_1 - 123101_4, 2013/12

 Times Cited Count:20 Percentile:63.69(Physics, Applied)

We demonstrate a large enhancement of critical current density ($$J$$$$_{rm c}$$) up to 1.0 $$times$$ 10$$^{7}$$ A/cm$$^{2}$$ at 5 K under self-field in (Ba,K)Fe$$_{2}$$As$$_{2}$$ single crystals by irradiating 320 MeV Au ions. With the very promising potential of this material in mind, we have fabricated a (Ba,K)Fe$$_{2}$$As$$_{2}$$ superconducting wire through a powder-in-tube method combined with the hot isostatic pressing technique, whose effectiveness has been proven in industrial Bi2223 tapes. The Jc in the wire at 4.2 K has reached 37 kA/cm$$^{2}$$ under self-field and 3.0 kA/cm$$^{2}$$ at 90 kOe. Magneto-optical imaging of the wire confirmed the large intergranular Jc in the wire core.

Journal Articles

Effects of irradiation-particle energy on critical current density in Co-doped BaFe$$_{2}$$As$$_{2}$$

Taen, Toshihiro*; Yagyuda, Hidenori*; Nakajima, Yasuyuki*; Tamegai, Tsuyoshi*; Okayasu, Satoru; Kitamura, Hisashi*; Murakami, Takeshi*; Laviano, F.*; Ghigo, G.*

Physica C, 484, p.62 - 65, 2013/01

 Times Cited Count:8 Percentile:37.42(Physics, Applied)

We report effects of particle energy on physical properties of Co-doped BaFe$$_{2}$$As$$_{2}$$ in the case of Xe and Au irradiations. The irradiation-induced suppression of $$T$$$$_{rm c}$$ is found to be related with several factors, such as defect structures and the thickness of the crystal. Heavy-ion irradiation induces enhancement of critical current density $$J$$$$_{rm c}$$, and a weak dip in the hysteresis loop. The fish-tail effect is completely suppressed by a modest density of defects. The enhancement of $$J$$$$_{rm c}$$ is closely related to the defect structure. Namely, splayed structure in columnar defects, inevitably introduced at lower energies, results in a strong enhancement of $$J$$$$_{rm c}$$ by forced entanglement of vortices.

Journal Articles

Effects of particle irradiations on vortex states in iron-based superconductors

Tamegai, Tsuyoshi*; Taen, Toshihiro*; Yagyuda, Hidenori*; Tsuchiya, Yuji*; Mohan, S.*; Taniguchi, Tomotaka*; Nakajima, Yasuyuki*; Okayasu, Satoru; Sasase, Masato*; Kitamura, Hisashi*; et al.

Superconductor Science and Technology, 25(8), p.084008_1 - 084008_14, 2012/08

 Times Cited Count:83 Percentile:93.33(Physics, Applied)

Various kinds of energetic particles are irradiated into iron-based superconductors, and their effects on the critical current density $$J$$$$_{rm c}$$ and vortex dynamics have been systematically studied. It is found that $$J$$$$_{rm c}$$ is enhanced and vortex dynamics is strongly suppressed by energetic particles having a sufficient energy deposition rate, similar to the case of high temperature cuprate superconductors. The enhancement of $$J$$$$_{rm c}$$, in general, persists up to much higher irradiation doses than in cuprates. However, details of the effect of irradiation depend on the kind of ion species and their energies. Even with the same ions and energies, the effect is not universal for different kinds of iron-based superconductors. The correlated nature of defects created by heavy-ion irradiation is confirmed by the angular dependence of irreversible magnetization.

Journal Articles

Separation in $$varepsilon$$-phase of BiPb alloy under mega-gravity

Okayasu, Satoru; Ono, Masao; Nishio, Taichiro*; Iguchi, Yusuke*; Mashimo, Tsutomu*

Defect and Diffusion Forum, 323-325, p.545 - 548, 2012/04

 Times Cited Count:0 Percentile:0.01

Atomic sedimentation in solid occurs under mega-gravity treatment. As the result, partially melt-growth in $$varepsilon$$-phase of BiPb-alloy occurs. Small difference of densities between fully hcp structure of Bi$$_{3}$$Pb$$_{7}$$ and that of partially defected Bi$$_{3}$$Pb$$_{(7-delta)}$$ are enhanced under mega-gravity, and cause the separation of the $$varepsilon$$-phase. Superconducting properties differs between the separated two phases.

Journal Articles

Effect of Si interlayers on the magnetic and mechanical properties of Fe/Ge neutron polarizing multilayer mirrors

Maruyama, Ryuji; Yamazaki, Dai; Okayasu, Satoru; Takeda, Masayasu; Zettsu, Nobuyuki*; Nagano, Mikinori*; Yamamura, Kazuya*; Hayashida, Hirotoshi; Soyama, Kazuhiko

Journal of Applied Physics, 111(6), p.063904_1 - 063904_10, 2012/03

 Times Cited Count:4 Percentile:18.32(Physics, Applied)

no abstracts in English

Journal Articles

Radiation effects on film formation and nanostructural changes of iron disilicide thin film

Sasase, Masato*; Yamamoto, Hiroyuki; Okayasu, Satoru

Nuclear Instruments and Methods in Physics Research B, 272, p.318 - 321, 2012/02

 Times Cited Count:0 Percentile:0.02(Instruments & Instrumentation)

Radiation effects for film formation and nanostructural changes of iron disilicide thin film have been discussed.

Journal Articles

Flux pinning properties of correlated pinning at low temperatures in ErBCO films with inclined columnar defects

Awaji, Satoshi*; Namba, Masashi*; Watanabe, Kazuo*; Kai, Hideki*; Mukaida, Masashi*; Okayasu, Satoru

Journal of Applied Physics, 111(1), p.013914_1 - 013914_4, 2012/01

 Times Cited Count:24 Percentile:69.81(Physics, Applied)

The effect of $$c$$-axis correlated pinning on the critical current density $$J$$$$_{c}$$ at low temperatures under high magnetic fields was investigated on the basis of the transport measurements of $$J$$$$_{c}$$ and irreversibility field B$$_{irr}$$ properties of an ErBa$$_{2}$$Cu$$_{3}$$O$$_{y}$$ film with inclined columnar defects. The contribution of correlated pinning on $$J$$$$_{c}$$ decreased drastically with decreasing temperature under high magnetic fields above the matching field. At low temperatures, the presence of a matching field limited the pinning force for correlated pinning, while the ratio of the maximum pinning force of the correlated pinning to the random one was proportional to the inverse of B$$_{irr}$$. In order to improve the critical current properties at low temperatures under high magnetic fields, an increase in the matching field and/or the introduction of strong random pinning are effective.

183 (Records 1-20 displayed on this page)