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Journal Articles

Triple axis spectrometers of JAEA

Osakabe, Toyotaka

Hamon, 31(1), p.14 - 17, 2021/02

no abstracts in English

Journal Articles

Origin of the large ferroelectric polarization enhancement under high pressure for multiferroic DyMnO$$_{3}$$ studied by polarized and unpolarized neutron diffraction

Terada, Noriki*; Qureshi, N.*; Stunault, A.*; Enderle, M.*; Ouladdiaf, B.*; Colin, C. V.*; Khalyavin, D. D.*; Manuel, P.*; Orlandi, F.*; Miyahara, Shin*; et al.

Physical Review B, 102(8), p.085131_1 - 085131_7, 2020/08

 Times Cited Count:2 Percentile:17.39(Materials Science, Multidisciplinary)

Journal Articles

Spherical neutron polarimetry under high pressure for a multiferroic delafossite ferrite

Terada, Noriki*; Qureshi, N.*; Chapon, L. C.*; Osakabe, Toyotaka

Nature Communications (Internet), 9, p.4368_1 - 4368_9, 2018/10

 Times Cited Count:5 Percentile:29.23(Multidisciplinary Sciences)

Journal Articles

Magnetic ordering in pressure-induced phases with giant spin-driven ferroelectricity in multiferroic TbMnO$$_{3}$$

Terada, Noriki*; Khalyavin, D. D.*; Manuel, P.*; Osakabe, Toyotaka; Kikkawa, Akiko*; Kitazawa, Hideaki*

Physical Review B, 93(8), p.081104_1 - 081104_5, 2016/02

 Times Cited Count:18 Percentile:66.03(Materials Science, Multidisciplinary)

We performed neutron diffraction experiments under high pressures and high magnetic fields using a single crystal of the multiferroic compound TbMnO$$_{3}$$ in order to clarify the mechanism associated with pressure/magnetic-field-induced giant ferroelectric polarization. We found that the E-type ordering of Mn spins induces giant ferroelectric polarization over all the parameter regions investigated, through an exchange striction mechanism. Furthermore, we propose that the polarization is reduced by polar ordering of the Tb moments in a zero magnetic field and is enhanced via the field-induced transition from polar to nonpolar Tb orderings at 2T.

Journal Articles

Development of technique for electrical insulation of metallic gasket using anodic oxide coating

Osakabe, Toyotaka; Kato, Yoshihiro*; Honmoto, Satoru*; Kuwahara, Keitaro*

Koatsuryoku No Kagaku To Gijutsu, 25(1), p.57 - 63, 2015/03

In this article, we describe an unique technique for electrical insulation of metallic gasket to perform simultaneous measurements of electrical resistivity and neutron diffraction under high pressure. The anodic oxide coating was adopted as the insulation layer of the aluminum (JIS A2017) gasket used in the hybrid-anvil device for neutron diffraction. In the feasibility tests of the coated gaskets, maximum pressure of about 6 GPa was generated without electrical breakdown of the coating or disconnection of Au leads.

Journal Articles

Beam-transport optimization for cold-neutron spectrometer

Nakajima, Kenji; Kawamura, Seiko; Kikuchi, Tatsuya; Kajimoto, Ryoichi; Takahashi, Nobuaki*; Nakamura, Mitsutaka; Soyama, Kazuhiko; Osakabe, Toyotaka

EPJ Web of Conferences, 83, p.03011_1 - 03011_5, 2015/01

 Times Cited Count:3 Percentile:73.67

We report the design of the beam-transport system (especially the vertical geometry) for a cold-neutron disk-chopper spectrometer AMATERAS at J-PARC. Based on the elliptical shape, which is one of the most effective geometries for a ballistic mirror, the design was optimized to obtain, at the sample position, a neutron beam with high flux without serious degrading in divergence and spacial homogeneity within the boundary conditions required from actual spectrometer construction. The optimum focal point was examined. An ideal elliptical shape was modified to reduce its height without serious loss of transmission. The final result was adapted to the construction requirements of AMATERAS. Although the ideas studied in this paper are considered for the AMATERAS case, they can be useful also to other spectrometers in similar situations.

Journal Articles

Pressure-induced polar phases in multiferroic delafossite CuFeO$$_{2}$$

Terada, Noriki*; Khalyavin, D. D.*; Manuel, P.*; Osakabe, Toyotaka; Radaelli, P. G.*; Kitazawa, Hideaki*

Physical Review B, 89(22), p.220403_1 - 220403_6, 2014/06


 Times Cited Count:29 Percentile:75.53(Materials Science, Multidisciplinary)

We have studied the pressure effect on the magnetic orderings in the strongly frustrated antiferromagnet CuFeO$$_{2}$$, by using neutron diffraction experiments under hydrostatic pressure. The main result is elucidation of the pressure-temperature magnetic phase diagram, consisting of the fourmagnetic phases including two polar ones. In particular, in the 3 GPa $$<$$ P $$<$$ 4 GPa pressure range, the ICM2 phase with the proper screw magnetic ordering stabilized. This polar phase is almost identical to the ferroelectric incommensurate (FEIC) phase induced by either a magnetic field or chemical doping. Furthermore, above 4 GPa, a new low-symmetry phase ICM3 is realized. This is unique for the family of delafossite multiferroics and implies an admixture of both cycloidal and proper screw spin configurations. The sequence of the observed magnetic phases with changing pressure might be attributed to pressure suppression of the monoclinic lattice distortions responsible for releasing the spin frustration in the system.

Journal Articles

High-pressure studies of DyB$$_2$$C$$_2$$

Yamauchi, Hiroki; Osakabe, Toyotaka; Kosaka, Masashi*; Matsuoka, Eiichi*; Onodera, Hideya*

Journal of the Korean Physical Society, 62(12), p.2084 - 2087, 2013/06

 Times Cited Count:1 Percentile:11.88(Physics, Multidisciplinary)

Journal Articles

Development of technique for high-pressure single-crystal neutron scattering and its application to studies of magnetic materials

Osakabe, Toyotaka

Hamon, 22(2), p.139 - 144, 2012/05

In this article, a new high-pressure apparatus for single-crystal magnetic neutron diffraction under 10 GPa is described. First, new hybrid-anvil, which is composed of an opposed pair of a supported SiC anvil and a tungsten carbide (WC) anvil with a center-dimpled culet, is introduced. Next, results of an investigation of pressure-transmitting media are shown. The hydrostaticity of the media is essential for the single-crystal diffraction experiments. Finally, a thermal neutron focusing device with a lot of curved supermirrors is shown. The device can compensate weak magnetic signals from tiny samples in high-pressure cells. As examples of the studies using the apparatus, the high-pressure single-crystal magnetic neutron diffraction experiments on 4f-electron systems PrFe$$_{4}$$P$$_{12}$$ and HoB$$_{2}$$C$$_{2}$$ are taken up.

Journal Articles

Pressure effects on quadrupolar and magnetic ordering in HoB$$_2$$C$$_2$$ observed by single-crystal neutron diffraction

Yamauchi, Hiroki; Osakabe, Toyotaka; Matsuoka, Eiichi*; Onodera, Hideya*

Journal of the Physical Society of Japan, 81(3), p.034715_1 - 034715_7, 2012/03

 Times Cited Count:11 Percentile:58.59(Physics, Multidisciplinary)

High-pressure single-crystal neutron diffraction experiments were carried out on a tetragonal HoB$$_2$$C$$_2$$ where the antiferroquadrupolar (AFQ) order coexists with the antiferromagnetic (AFM) order competitively. The transition temperature $$T$$$$_{rm N}$$ increases monotonically with increasing pressure up to 9.8 GPa, whereas $$T$$$$_{rm Q}$$ decreases and vanishes at approximately 4 GPa as pressure increases, indicating that applying pressure enhances the AFM interaction and simultaneously suppresses the AFQ order. We presume that the volume shrinkage by applying pressure constrains the local atomic displacement of (B-C) layers and leads to the suppression of the AFQ order. We additionally found pressure-induced phases where the ordered state was considered to be antiferromagnetic.

Journal Articles

Magnetic phase diagrams of YVO$$_{3}$$ and TbVO$$_{3}$$ under high pressure

Bizen, Daisuke*; Nakao, Hironori*; Iwasa, Kazuaki*; Murakami, Yoichi*; Osakabe, Toyotaka; Fujioka, Jun*; Yasue, Toshio*; Miyasaka, Shigeki*; Tokura, Yoshinori*

Journal of the Physical Society of Japan, 81(2), p.024715_1 - 024715_6, 2012/02

 Times Cited Count:6 Percentile:43.76(Physics, Multidisciplinary)

The magnetic phase diagrams for $$R$$VO$$_{3}$$ ($$R$$ = Y, Tb) were determined by low temperature and high pressure neutron-diffraction techniques. We found that the magnetic ground state in TbVO$$_{3}$$ changes from ${it C}$-type spin ordering (${it C}$-SO) to ${it G}$-type spin ordering (${it G}$-SO) on application of pressure. The transition of the magnetic ground state also indicates that the ground state of the orbital ordering changes from ${it G}$-type orbital ordering (${it G}$-OO) to ${it C}$-type orbital ordering (${it C}$-OO). In YVO$$_{3}$$, the ${it G}$-SO and ${it C}$-OO phases set in simultaneously up to 6.2 GPa, and the disorder-[${it G}$-SO, ${it C}$-OO] phase transition appears above 6 GPa. This is the first observation of a simultaneous spin and orbital order-disorder phase transition in perovskite-type transition-metal oxides $$R$$MO$$_{3}$$. The [${it G}$-SO, ${it C}$-OO] phase is strongly stabilized with increasing pressure, and both the covalency effect and the superexchange interaction play roles in this stabilization.

Journal Articles

Magnetic correlations and the influence of atomic disorder in frustrated isosceles triangular lattice antiferromagnet CuMnO$$_2$$

Terada, Noriki*; Tsuchiya, Yoshinori*; Kitazawa, Hideaki*; Osakabe, Toyotaka; Metoki, Naoto; Igawa, Naoki; Oyama, Kenji*

Physical Review B, 84(6), p.064432_1 - 064432_8, 2011/08

 Times Cited Count:17 Percentile:58.98(Materials Science, Multidisciplinary)

We have studied the magnetic correlations of the isosceles triangular lattice antiferromagnet CuMnO$$_2$$. Above $$T$$$$_{rm N}$$, the magnetic correlations are characterized by a two-dimensional (2D) short-range correlation. Below $$T$$$$_{rm N}$$, the magnetic structures have been identified to be collinear with the magnetic moments almost parallel to the $$d_{z^2}$$ orbitals. The stacking sequence along the $$c$$ direction is changed from antiferromagnetic to ferromagnetic by atomic disorder. We find that the second-nearest-neighbor interlayer interaction plays an important role for the magnetic stacking along the $$c$$ axis. The magnetic excitation below $$T$$$$_{rm N}$$ is characterized by collective spin-wave excitation with an energy gap of 6 meV from the three-dimensional long-range magnetic order and by spin-liquid-like 2D excitation, indicated by specific heat.

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:112 Percentile:95.27(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

High-pressure suppression of long-range magnetic order in the triangular-lattice antiferromagnet CuFeO$$_{2}$$

Terada, Noriki*; Osakabe, Toyotaka; Kitazawa, Hideaki*

Physical Review B, 83(2), p.020403_1 - 020403_4, 2011/01

 Times Cited Count:12 Percentile:48.24(Materials Science, Multidisciplinary)

We succeeded in observing pressure-suppressed magnetic long-range ordering (LRO) in the triangular-lattice antiferromagnet CuFeO$$_{2}$$, using neutron-diffraction experiments under an isotropic pressure. The magnetic LRO of the four-sublattice ground state under ambient pressure in CuFeO$$_{2}$$ almost disappears at the high pressure of 7.9 GPa, and is replaced by an incommensurate order with temperature-independent wave number of (0.192 0.192 1.5). The incommensurate wave number observed at 7.9 GPa corresponds to that observed just above the temperature at which lattice distortion and magnetic LRO simultaneously occur under ambient pressure. Therefore, the long-range magnetic ordering disappears because the high pressure suppressed the lattice distortion that otherwise relieves spin frustration and leads the spin system to LRO.

Journal Articles

Stress and temperature dependence of the structure of the martensite and X-phase in Ni$$_{2}$$MnGa

Fukuda, Takashi*; Terai, Tomoyuki*; Kushida, Hiroaki*; Kakeshita, Tomoyuki*; Osakabe, Toyotaka; Kakurai, Kazuhisa

Philosophical Magazine, 90(14), p.1925 - 1935, 2010/05

 Times Cited Count:6 Percentile:37.97(Materials Science, Multidisciplinary)

The stress and temperature dependence of the structure of the X-phase in Ni$$_{2}$$MnGa has been investigated by neutron diffraction measurements under compressive stress to clarify the structural relationship among the P-, I-, M- and X-phases. The structure of the X-phase in Ni$$_{2}$$MnGa depends strongly on stress and temperature compared to the M- or I-phase. In association with the X $$rightarrow$$ M transformation, both the position and intensity of the satellite reflection changes drastically, regardless of stress and temperature, while with X $$rightarrow$$ P transformation, the intensity of the satellite reflection fades gradually. For the I $$rightarrow$$ X transformation, the position and intensity of the satellite changes drastically when transformation occur under compressive stress, while the changes are continuous under zero stress. These results strongly suggest the existence of a multicritical point in Ni$$_{2}$$MnGa.

Journal Articles

Large-volume static compression using nano-polycrystalline diamond for opposed anvils in compact cells

Okuchi, Takuo*; Sasaki, Shigeo*; Osakabe, Toyotaka; Ono, Yoshiki*; Odake, Shoko*; Kagi, Hiroyuki*

Journal of Physics; Conference Series, 215, p.012188_1 - 012188_9, 2010/03

 Times Cited Count:5 Percentile:85.8

We prepared super-hard nano-polycrystalline diamond (NPD) anvils for large-volume compression for intrinsically low-sensitivity methods of measurement, such as neutron scattering and NMR. These anvils are harder, larger and stronger than single crystal diamond anvils, so that they could play an ideal role to accept the larger forces. We tested supported and unsupported anvil geometries separately by using two types of compact high-pressure cells and could generate the pressure of 14 GPa for the sample volume of 0.1 mm$$^{3}$$ or more. The test results demonstrate a large future potential of NPD anvils for large-volume compression.

Journal Articles

Pressure-induced antiferromagnetic order in filled skutterudite PrFe$$_{4}$$P$$_{12}$$ studied by single-crystal high-pressure neutron diffraction

Osakabe, Toyotaka; Kuwahara, Keitaro*; Kawana, Daichi*; Iwasa, Kazuaki*; Kikuchi, Daisuke*; Aoki, Yuji*; Kogi, Masafumi*; Sato, Hideyuki*

Journal of the Physical Society of Japan, 79(3), p.034711_1 - 034711_7, 2010/03

 Times Cited Count:18 Percentile:69.39(Physics, Multidisciplinary)

Journal Articles

Development of high-pressure technique for single-crystal magnetic neutron diffraction under 10 GPa

Osakabe, Toyotaka; Yamauchi, Hiroki; Okuchi, Takuo*

Koatsuryoku No Kagaku To Gijutsu, 20(1), p.72 - 75, 2010/02

A new hybrid-type anvil technique for high-pressure single-crystal magnetic neutron diffraction under 10 GPa is described. The hybrid anvil is composed of an opposed pair of two kinds of anvils. One is a large sapphire anvil or a supported SiC anvil and the other is a tungsten carbide (WC) anvil which has a hollow in the center of the culet. In a feasibility test of the hybrid anvil, we could generate the pressure up to 10 GPa at the load of 3.8 tons with high stability.

Journal Articles

Structural relation between the X-phase and other phases in Ni$$_{2}$$MnGa

Kakeshita, Tomoyuki*; Fukuda, Takashi*; Terai, Tomoyuki*; Osakabe, Toyotaka; Kakurai, Kazuhisa

Materials Science Forum, 635, p.49 - 54, 2009/12

We have investigated stress and temperature dependences of the structure of the X-phase in Ni$$_{2}$$MnGa to understand structural relation between the X-phase and other phases. We found that the structure change associated with the transformation from the intermediate (I-) phase to the X-phase is discontinuous under a compressive stress, while it is continuous under zero stress. In addition, the transformation from the X-phase to the L2$$_{1}$$-type parent phase is continuous regardless of applied stress. These results strongly suggest the existence of multi-critical point in Ni$$_{2}$$MnGa.

Journal Articles

Incommensurate structures of intermediate phase and martensite phase in Ni$$_{2}$$MnGa

Kushida, Hiroaki*; Fukuda, Kodai*; Terai, Tomoyuki*; Fukuda, Takashi*; Kakeshita, Tomoyuki*; Oba, Takuya*; Osakabe, Toyotaka; Kakurai, Kazuhisa; Kato, Kenichi*

Journal of Physics; Conference Series, 165, p.012054_1 - 012054_4, 2009/06

135 (Records 1-20 displayed on this page)