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Journal Articles

$$q$$=0 long-range magnetic order in centennialite CaCu$$_{3}$$(OD)$$_{6}$$Cl$$_{2}$$ $$cdot$$ 0.6D$$_{2}$$O; A Spin-$$frac{1}{2}$$ perfect kagome antiferromagnet with $$J_{1}$$-$$J_{2}$$-$$J_{d}$$

Iida, Kazuki*; Yoshida, Hiroyuki*; Nakao, Akiko*; Jeschke, H. O.*; Iqbal, Y.*; Nakajima, Kenji; Kawamura, Seiko; Munakata, Koji*; Inamura, Yasuhiro; Murai, Naoki; et al.

Physical Review B, 101(22), p.220408_1 - 220408_6, 2020/06

 Times Cited Count:6 Percentile:75.71(Materials Science, Multidisciplinary)

Crystal and magnetic structures of the mineral centennialite CaCu$$_{3}$$(OD)$$_{6}$$Cl$$_{2}$$ $$cdot$$ 0.6D$$_{2}$$O are investigated by means of synchrotron X-ray diffraction and neutron diffraction measurements complemented by density functional theory (DFT) and pseudofermion functional renormalization group (PFFRG) calculations. In CaCu$$_{3}$$(OD)$$_{6}$$Cl$$_{2}$$ $$cdot$$ 0.6D$$_{2}$$O, Cu$$^{2+}$$ ions form a geometrically perfect kagome network with antiferromagnetic $$J_{1}$$. No intersite disorder between Cu$$^{2+}$$ and Ca$$^{2+}$$ ions is detected. CaCu$$_{3}$$(OD)$$_{6}$$Cl$$_{2}$$ $$cdot$$ 0.6D$$_{2}$$O enters a magnetic long-range ordered state below $$T_{rm N}$$ = 7.2 K, and the $$q$$=0 magnetic structure with negative vector spin chirality is obtained. The ordered moment at 0.3 K is suppressed to 0.58(2)$$mu$$B. Our DFT calculations indicate the presence of antiferromagnetic $$J_{2}$$ and ferromagnetic $$J_{d}$$ superexchange couplings of a strength which places the system at the crossroads of three magnetic orders (at the classical level) and a spin-$$frac{1}{2}$$ PFFRG analysis shows a dominance of $$q$$=0 type magnetic correlations, consistent with and indicating proximity to the observed $$q$$=0 spin structure. The results suggest that this material is located close to a quantum critical point and is a good realization of a $$J_{1}$$-$$J_{2}$$-$$J_{d}$$ kagome antiferromagnet.

Journal Articles

Phase-transition kinetics of magnetic skyrmions investigated by stroboscopic small-angle neutron scattering

Nakajima, Taro*; Inamura, Yasuhiro; Ito, Takayoshi*; Oishi, Kazuki*; Oike, Hiroshi*; Kagawa, Fumitaka*; Kikkawa, Akiko*; Taguchi, Yasujiro*; Kakurai, Kazuhisa*; Tokura, Yoshinori*; et al.

Physical Review B, 98(1), p.014424_1 - 014424_5, 2018/07

 Times Cited Count:4 Percentile:32.53(Materials Science, Multidisciplinary)

We investigated the phase-transition kinetics of magnetic skyrmion lattice (SkL) in MnSi by means of stroboscopic small-angle neutron scattering (SANS). Temporal evolutions of SANS patterns were measured with time resolution of 13 ms while sweeping temperature as fast as 50 Ks$$^{-1}$$. It turned out that the paramagnetic-to-SkL transition immediately occurs upon traversing the equilibrium phase boundary on the rapid cooling, whereas the SkL-to-conical transition can be kinetically avoided to realize the low-temperature metastable SkL with a long-range magnetic order. The formation of the metastable SkL was found to be strongly dependent not only on cooling rate, but also on magnetic eld and trajectory in the H-T phase diagram.

Journal Articles

Structure of the magnetic excitations in the spin-1/2 triangular-lattice Heisenberg antiferromagnet Ba$$_{3}$$CoSb$$_{2}$$O$$_{9}$$

Ito, Saya*; Kurita, Nubuyuki*; Tanaka, Hidekazu*; Kawamura, Seiko; Nakajima, Kenji; Ito, Shinichi*; Kuwahara, Keitaro*; Kakurai, Kazuhisa*

Nature Communications (Internet), 8, p.235_1 - 235_6, 2017/08

 Times Cited Count:44 Percentile:93.33(Multidisciplinary Sciences)

Journal Articles

Interaction of spin-orbital-lattice degrees of freedom; Vibronic state of the corner-sharing-tetrahedral frustrated spin system HoBaFe$$_{4}$$O$$_{7}$$ by dynamical Jahn-Teller effect

Kamazawa, Kazuya*; Ishikado, Motoyuki*; Kawamura, Seiko; Kawakita, Yukinobu; Kakurai, Kazuhisa*; Nakajima, Kenji; Sato, Masashi*

Physical Review B, 95(10), p.104413_1 - 104413_7, 2017/03

 Times Cited Count:2 Percentile:15.91(Materials Science, Multidisciplinary)

Journal Articles

Effects of Mg, Ag, and Al substitutions on magnetic excitations in the triangular-lattice antiferromagnet CuCrO$$_{2}$$

Kajimoto, Ryoichi; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Kakurai, Kazuhisa; Hokazono, Takahisa*; Ozono, Akira*; Okuda, Tetsuji*

Journal of the Physical Society of Japan, 82(5), p.054702_1 - 054702_6, 2013/05

 Times Cited Count:4 Percentile:36.94(Physics, Multidisciplinary)

Journal Articles

Uniaxial-pressure control of magnetic phase transitions in a frustrated magnet CuFe$$_{1-x}$$Ga$$_{x}$$O$$_{2}$$ (x =0, 0.018)

Nakajima, Taro*; Mitsuda, Setsuo*; Takahashi, Keiichiro*; Yoshitomi, Keisuke*; Masuda, Kazuya*; Kaneko, Chikafumi*; Homma, Yuki*; Kobayashi, Satoru*; Kitazawa, Hideaki*; Kosaka, Masashi*; et al.

Journal of the Physical Society of Japan, 81(9), p.094710_1 - 094710_8, 2012/09

Journal Articles

Uniaxial-pressure control of magnetic phase transitions in a frustrated magnet CuFe$$_{1-x}$$Ga$$_{x}$$O$$_{2}$$ ($$x$$ = 0, 0.018)

Nakajima, Taro*; Mitsuda, Setsuo*; Takahashi, Keiichiro*; Yoshitomi, Keisuke*; Masuda, Kazuya*; Kaneko, Chikafumi*; Homma, Yuki*; Kobayashi, Satoru*; Kitazawa, Hideaki*; Kosaka, Masashi*; et al.

Journal of the Physical Society of Japan, 81(9), p.094710_1 - 094710_8, 2012/09

 Times Cited Count:12 Percentile:62.78(Physics, Multidisciplinary)

Journal Articles

ToF inelastic neutron scattering studies on quantum spin systems (CuCl)La$$B_2$$O$$_7$$ ($$B$$ = Nb, Ta)

Kawamura, Seiko; Nakajima, Kenji; Inamura, Yasuhiro; Tsujimoto, Yoshihiro*; Kitada, Atsushi*; Takeiri, Fumitaka*; Kageyama, Hiroshi*; Ajiro, Yoshitami*; Nishi, Masakazu*; Kakurai, Kazuhisa

Journal of Physics; Conference Series, 320, p.012037_1 - 012037_5, 2011/09

 Times Cited Count:0 Percentile:0.03

The magnetic ground state of (CuCl)LaNb$$_2$$O$$_7$$ has been suggested to be a spin-singlet state with an excitation gap of $$Delta E sim 2.3$$ meV, while (CuCl)LaTa$$_2$$O$$_7$$ has an antiferromagnetic (AFM) ground state. The systems are suspected to be a frustrated quantum spin system due to the competition between the nearest and next-nearest exchange interactions. We have studied magnetic excitation in these systems by ToF inelastic neutron scattering technique. The measurements were performed on powder samples of (CuCl)LaNb$$_2$$O$$_7$$ and (CuCl)LaTa$$_2$$O$$_7$$ at a disk-chopper-type spectrometer AMATERAS in J-PARC. In both systems, a band-like excitation was observed at $$Delta E sim 2$$ meV. The $$Q$$ dependence of the intensity of magnetic excitation around 2 meV for (CuCl)LaNb$$_2$$O$$_7$$ well reproduces that observed at a triple-axis spectrometer, exhibiting characteristics of spin-singlet dimers. On the other hand, (CuCl)LaTa$$_2$$O$$_7$$ in the AFM state exhibits a different $$Q$$ dependence.

Journal Articles

AMATERAS; A Cold-neutron disk chopper spectrometer

Nakajima, Kenji; Kawamura, Seiko; Kikuchi, Tatsuya; Nakamura, Mitsutaka; Kajimoto, Ryoichi; Inamura, Yasuhiro; Takahashi, Nobuaki; Aizawa, Kazuya; Suzuya, Kentaro; Shibata, Kaoru; et al.

Journal of the Physical Society of Japan, 80(Suppl.B), p.SB028_1 - SB028_6, 2011/05

 Times Cited Count:90 Percentile:94.38(Physics, Multidisciplinary)

AMATERAS is a cold-neutron disk-chopper spectrometer in MLF, J-PARC. The construction of main part of the spectrometer has been completed in spring of 2009. Soon after that, we have started the commissioning work on AMATERAS. The performance of AMATERAS has been examined by test experiments in the course of commissioning. In parallel to these works, we have started the user program on AMATERAS from December 2009 and we are getting scientific results from our spectrometer. In this presentation, we will report the current status of AMATERAS including the results of performance tests and some of examples of scientific outputs.

Journal Articles

Temperature and Ag doping effect on magnetic excitations in the quasi-two-dimensional triangular lattice antiferromagnet CuCrO$$_2$$ studied by inelastic neutron scattering

Kajimoto, Ryoichi; Nakajima, Kenji; Kawamura, Seiko; Inamura, Yasuhiro; Kakurai, Kazuhisa; Arai, Masatoshi; Hokazono, Takahisa*; Ozono, Akira*; Okuda, Tetsuji*

Journal of the Physical Society of Japan, 79(12), p.123705_1 - 123705_4, 2010/12

 Times Cited Count:21 Percentile:74(Physics, Multidisciplinary)

Journal Articles

Exchange-striction associated with the elliptical proper helical magnetic structure in the ferroelectric phase of CuFe$$_{1-y}$$Ga$$_{y}$$O$$_{2}$$

Terada, Noriki*; Nakajima, Taro*; Mitsuda, Setsuo*; Matsuda, Masaaki; Kakurai, Kazuhisa; Tanaka, Yoshihito*; Kitazawa, Hideaki*

Journal of Physics; Conference Series, 211(1), p.012005_1 - 012005_6, 2010/01

 Times Cited Count:2 Percentile:69.52

Journal Articles

Improvement of the quality and stability of electron bunch using countercrossing laser beam

Kotaki, Hideyuki; Daito, Izuru; Kando, Masaki; Hayashi, Yukio; Ma, J.-L.; Chen, L.-M.; Esirkepov, T. Z.; Fukuda, Yuji; Homma, Takayuki; Pirozhkov, A. S.; et al.

IEEE Transactions on Plasma Science, 36(4), p.1760 - 1764, 2008/08

 Times Cited Count:8 Percentile:34.65(Physics, Fluids & Plasmas)

The counter-crossing injection, which is a realistic setup for applications, by two sub-relativistic laser pulses colliding is demonstrated in sub-relativistic intensity laser pulse interaction with plasma. The laser pulses in plasma are self-focused to higher intensity when the laser power is above the threshold of a relativistic self-focusing. The collision of self-focused laser pulses generates a high-quality electron beam with high repeatability. The generated monoenergetic electron beam has 14 MeV of the peak energy, 11% of the energy spread, 22 pC of the charge, 1.6$$pi$$mm mrad of the normalized emittance, and 50% of the repeatability.

Journal Articles

Counter-crossing injection for stable high-quality electron beam generation via laser-plasma interaction

Kotaki, Hideyuki; Daito, Izuru; Hayashi, Yukio; Ma, J.-L.; Chen, L.-M.; Kando, Masaki; Esirkepov, T. Z.; Fukuda, Yuji; Homma, Takayuki; Pirozhkov, A. S.; et al.

Journal of Physics; Conference Series, 112(4), p.042031_1 - 042031_4, 2008/00

 Times Cited Count:1 Percentile:58.25

Laser-driven plasma accelerators have been conceived to be the next-generation particle accelerators, promising ultrahigh field particle acceleration with a very short duration electron beam. In the case of electron beam generation by using one laser pulse via wavebreaking, however, it is not stable. In order to generate a stable high-quality electron beam, optical injection by collision of two laser pulses is proposed. Recently, the electron generation with this approach was demonstrated. The experiment was carried out by the perfect head-on collision, which has problems to the backward laser light and the extraction of the generated electron beam. The counter-crossing injection, which is a realistic setup for applications, by two sub-relativistic laser pulses collision with the colliding angle of 45$$^{circ}$$ is demonstrated. The collision of two laser pulses generates a high-quality electron beam with high repeatability. The generated monoenergetic electron beam has 14.4 MeV of the peak energy, 10.6% of the energy spread, 21.8 pC of the charge, 1.6 $$pi$$ mm mrad of the normalized emittance, and 47.4% of the repeatability.

Journal Articles

Elongation of plasma channel for electron acceleration

Chen, L.-M.; Nakajima, Kazuhisa; Hong, W.*; Hua, J. F.*; Kameshima, Takashi; Kotaki, Hideyuki; Sugiyama, Kiyohiro*; Wen, X.*; Wu, Y.*; Tang, C.*; et al.

Chinese Optics Letters, 5(S1), p.S133 - S135, 2007/05

Journal Articles

Self-guiding of 100 TW femtosecond laser pulses in centimeter-scale underdense plasma

Chen, L.-M.; Kotaki, Hideyuki; Nakajima, Kazuhisa*; Koga, J. K.; Bulanov, S. V.; Tajima, Toshiki; Gu, Y. Q.*; Peng, H. S.*; Wang, X. X.*; Wen, T. S.*; et al.

Physics of Plasmas, 14(4), p.040703_1 - 040703_4, 2007/04

 Times Cited Count:36 Percentile:78.52(Physics, Fluids & Plasmas)

An experiment for the laser self-guiding studies has been carried out with 100 TW laser pulse interaction with the long underdense plasma. Formation of extremely long plasma channel with its length, about 10 mm, 20 times above the Rayleigh length is observed. The self-focusing channel features such as the laser pulse significant bending and the electron cavity formation are demonstrated experimentally for the first time.

Journal Articles

Cold-neutron disk-chopper spectrometer at J-PARC

Nakajima, Kenji; Nakamura, Mitsutaka; Kajimoto, Ryoichi; Osakabe, Toyotaka; Kakurai, Kazuhisa; Matsuda, Masaaki; Metoki, Naoto; Wakimoto, Shuichi; Sato, Taku*; Ito, Shinichi*; et al.

Journal of Neutron Research, 15(1), p.13 - 21, 2007/03

no abstracts in English

Journal Articles

Focusing quality of a split short laser pulse

Kotaki, Hideyuki; Oishi, Yuji*; Nayuki, Takuya*; Fujii, Takashi*; Nemoto, Koshichi*; Nakajima, Kazuhisa

Review of Scientific Instruments, 78(3), p.036102_1 - 036102_3, 2007/03

 Times Cited Count:0 Percentile:0.01(Instruments & Instrumentation)

no abstracts in English

Journal Articles

20 MeV quasi-monoenergetic electron beam production by using JLITE-X laser system at JAEA-APRC

Mori, Michiaki; Kando, Masaki; Daito, Izuru; Kotaki, Hideyuki; Hayashi, Yukio; Ogura, Koichi; Sagisaka, Akito; Esirkepov, T. Z.; Nakajima, Kazuhisa; Daido, Hiroyuki; et al.

International Journal of Modern Physics B, 21(3&4), p.407 - 414, 2007/02

 Times Cited Count:0 Percentile:0.01(Physics, Applied)

The quasi-monoenergetic electron beam produced by intense laser-plasma interaction was observed at plasma densities from $$4.1 times 10^{19} cm^{-3}$$ to $$5.0 times 10^{19} cm^{-3}$$. The terawatt laser beam was focused by using an off-axis parabolic mirror with f=648 mm. We observed quasi-monoenergetic electron beams in the forward direction. The peak energy of quasi-monoenergetic component of the electron beam was increased from 9 MeV to $$sim$$20 MeV with a energy spread of $$sim$$ 20$$%$$ increasing the plasma density from $$4.1 times 10^{19} cm^{-3}$$ to $$5.0 times 10^{19} cm^{-3}$$. However, the quasi-monoenergetic component of the electron beam disappeared at a plasma density of $$6.6 times 10^{19} cm^{-3}$$, and non-equilibrium (non Maxwellian) spectrum of the electron beam was observed. The table-top laser driven fs quasi-monoenergetic electron beam which is applicable to variety of fields has been demonstrated.

Journal Articles

Experimental study on $$K$$$$_{alpha}$$ X-ray emission from intense femtosecond laser-solid interactions

Xu, M. H.*; Chen, L.-M.; Li, Y.-T.*; Yuan, X.-H.*; Liu, Y.-Q.*; Nakajima, Kazuhisa; Tajima, Toshiki; Wang, Z.-H.*; Wei, Z.-Y.*; Zhao, W.*; et al.

Acta Physica Sinica, 56(1), p.353 - 358, 2007/01

The characteristics of $$K$$$$_{alpha}$$ X-ray sources generated by p-polarized femtosecond laser-solid interactions are experimentally studied in the relativistic regime. By use of knife-edge image technique and a single-photon-counting X-ray CCD camera, we obtain the source size, the spectrum and the conversion efficiency of the $$K$$$$_{alpha}$$ X-ray sources. The experimental results show that the conversion efficiency of $$K$$$$_{alpha}$$ photons reaches an optimum value 7.08$$times$$10$$^{-6}$$/sr at the laser intensity of 1.6$$times$$10$$^{18}$$W/cm$$^{2}$$, which is different from the Reich's simulation results. We find that about 10% of laser energy is converted into the forward hot electrons at the laser intensity of 1.6$$times$$10$$^{18}$$W/cm$$^{2}$$.

Journal Articles

Transverse dynamics and energy tuning of fast electrons generated in sub-relativistic intensity laser pulse interaction with plasmas

Mori, Michiaki; Kando, Masaki; Daito, Izuru; Kotaki, Hideyuki; Hayashi, Yukio; Yamazaki, Atsushi; Ogura, Koichi; Sagisaka, Akito; Koga, J. K.; Nakajima, Kazuhisa; et al.

Physics Letters A, 356(2), p.146 - 151, 2006/07

 Times Cited Count:45 Percentile:84.27(Physics, Multidisciplinary)

The regimes of quasi-mono-energetic electron beam generation were experimentally studied inthe sub-relativistic intensity laser plasma interaction. The observed electron acceleration regime is unfolded with two-dimensional-particle-in-cell simulations of laser-wakefield generation in the self-modulation regime.

95 (Records 1-20 displayed on this page)