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Journal Articles

Spin-flop phase in a honeycomb antiferromagnet Mn$$_{0.84}$$Mg$$_{0.16}$$TiO$$_{3}$$

Shamoto, Shinichi; Yamauchi, Hiroki; Ikeuchi, Kazuhiko*; Lee, M. K.*; Chang, L.-J.*; Garlea, V. O.*; Hwang, I. Y.*; Lee, K. H.*; Chung, J.-H.*

Journal of the Physical Society of Japan, 90(9), p.093703_1 - 093703_4, 2021/09

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

no abstracts in English

Journal Articles

Magnetic structure of short-range ordering in intermetallic antiferromagnet Mn$$_3$$RhSi

Kodama, Katsuaki; Honda, Takashi*; Yamauchi, Hiroki; Shamoto, Shinichi*; Ikeda, Kazutaka*; Otomo, Toshiya*

Journal of the Physical Society of Japan, 90(7), p.074710_1 - 074710_7, 2021/07

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

Journal Articles

Spin wave excitations in honeycomb antiferromagnet MnTiO$$_{3}$$

Hwang, I. Y.*; Lee, K. H.*; Chung, J.-H.*; Ikeuchi, Kazuhiko*; Garlea, V. O.*; Yamauchi, Hiroki; Akatsu, Mitsuhiro*; Shamoto, Shinichi

Journal of the Physical Society of Japan, 90(6), p.064708_1 - 064708_6, 2021/06

 Times Cited Count:1 Percentile:72.06(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Origin of magnetovolume effect in a cobaltite

Miao, P.*; Tan, Z.*; Lee, S. H.*; Ishikawa, Yoshihisa*; Torii, Shuki*; Yonemura, Masao*; Koda, Akihiro*; Komatsu, Kazuki*; Machida, Shinichi*; Sano, Asami; et al.

Physical Review B, 103(9), p.094302_1 - 094302_18, 2021/03

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

The layered perovskite PrBaCo$$_{2}$$O$$_{5.5}$$ demonstrates a strong negative thermal expansion (NTE) which holds potential for being fabricated into composites with zero thermal expansion. The NTE was found to be intimately associated with the spontaneous magnetic ordering, known as magneto-volume effect (MVE). Here we report with compelling evidences that the continuous-like MVE in PrBaCo$$_{2}$$O$$_{5.5}$$ is intrinsically of discontinuous character, originating from an magnetoelectric transition from an antiferromagnetic insulating large-volume (AFILV) phase to a ferromagnetic less-insulating small-volume (FLISV) phase. Furthermore, the magnetoelectric effect (ME) shows high sensitivity to multiple external stimuli such as temperature, carrier doping, hydrostatic pressure, magnetic field etc. In contrast to the well-known ME such as colossal magnetoresistance and multi-ferroic effect which involve symmetry breaking of crystal structure, the ME in the cobaltite is purely isostructural. Our discovery provides a new path way to realizing the ME as well as the NTE, which may find applications in new techniques.

Journal Articles

Broken C$$_{4}$$ symmetry in the tetragonal state of uniaxial strained BaCo$$_{0.9}$$Ni$$_{0.1}$$S$$_{1.9}$$

Shamoto, Shinichi; Yamauchi, Hiroki; Ikeuchi, Kazuhiko*; Kajimoto, Ryoichi; Ieda, Junichi

Physical Review Research (Internet), 3(1), p.013169_1 - 013169_9, 2021/02

Journal Articles

High-temperature short-range order in Mn$$_3$$RhSi

Yamauchi, Hiroki; Sari, D. P.*; Watanabe, Isao*; Yasui, Yukio*; Chang, L.-J.*; Kondo, Keietsu; Ito, Takashi; Ishikado, Motoyuki*; Hagiwara, Masato*; Frontzek, M. D.*; et al.

Communications Materials (Internet), 1, p.43_1 - 43_6, 2020/07

High-temperature short-range order is discovered up to 720 K in Mn$$_3$$RhSi by complementary use of neutron scattering and muon spin relaxation measurements.

Journal Articles

The $$f$$-electron state of the heavy fermion superconductor NpPd$$_5$$Al$$_2$$ and the isostructural family

Metoki, Naoto; Aczel, A. A.*; Aoki, Dai*; Chi, S.*; Fernandez-Baca, J. A.*; Griveau, J.-C.*; Hagiwara, Masato*; Hong, T.*; Haga, Yoshinori; Ikeuchi, Kazuhiko*; et al.

JPS Conference Proceedings (Internet), 30, p.011123_1 - 011123_6, 2020/03

Rare earths (4$$f$$) and actinides (5$$f$$) provide variety of interesting states realized with competing interactions between the increasing number of $$f$$ electrons. Since crystal field splitting of many-body $$f$$ electron system is smaller than the bandwidth, (1) high resolution experiments are needed, (2) essentially no clear spectrum with well defined peaks is expected in itinerant Ce and U compounds, and (3) Np and Pu is strictly regulated. Therefore, systematic research on magnetic excitations by neutron scattering experiments of localized compounds and rare earth iso-structural reference is useful. We describe the $$f$$ electron states of heavy electron compounds NpPd$$_5$$Al$$_2$$ and actinide and rare earth based iso-structural family.

Journal Articles

$$f$$-electron states in PrPd$$_5$$Al$$_2$$

Metoki, Naoto; Yamauchi, Hiroki; Suzuki, Hiroyuki*; Kitazawa, Hideaki*; Hagiwara, Masato*; Masuda, Takatsugu*; Aczel, A. A.*; Chi, S.*; Hong, T.*; Matsuda, Masaaki*; et al.

Journal of the Physical Society of Japan, 87(9), p.094704_1 - 094704_8, 2018/09

 Times Cited Count:5 Percentile:54.08(Physics, Multidisciplinary)

The $$f$$-electron states of PrPd$$_5$$Al$$_2$$ were revealed by neutron inelastic scattering. The flat $$f$$-orbitals with large $$J_z$$ become stable under the two-dimensional CEF potential of unique crystal structure, which is the origin of the Ising anisotropy. A systematic understanding is possible in RPd$$_5$$Al$$_2$$ based on this CEF potential. Especially the $$XY$$-type anisotropy in NpPd$$_5$$Al$$_2$$ can be qualitatively understood with the positive Stevens factors. It mean that the local property is important for the physical properties of RPd$$_5$$Al$$_2$$ including the heavy fermion superconductivity in NpPd$$_5$$Al$$_2$$.

Journal Articles

Neutron inelastic scattering study of the $$f$$-electron states in NdPd$$_5$$Al$$_2$$

Metoki, Naoto; Yamauchi, Hiroki; Suzuki, Hiroyuki*; Kitazawa, Hideaki*; Kamazawa, Kazuya*; Ikeuchi, Kazuhiko*; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro

Journal of the Physical Society of Japan, 87(8), p.084708_1 - 084708_7, 2018/08

 Times Cited Count:5 Percentile:54.08(Physics, Multidisciplinary)

Inelastic neutron scattering experiments were carried out in order to study the $$f$$-electron states of NdPd$$_5$$Al$$_2$$The CEF levels at 0K, 35.4K, 88.3K, 101.5K, and 198.8K were clarified from the excitation spectra. The $$Gamma_6$$ ground state contains the orbital with $$J_z=pm9/2$$ as a main component due to a large negative B$$_{20}=-1.4$$K, which is the origin of the strong uniaxial anisotropy. The estimated magnetic moment, the calculated susceptibility, magnetization curve, and specific heat are in good agreement with the experimental data. The existence of a common charge distribution with CePd$$_5$$Al$$_2$$ and PrPd$$_5$$Al$$_2$$. Indicates that a localized character is important even in actinide-based iso-structural compounds as actually observed in UPd$$_5$$Al$$_2$$ and also NpPd$$_5$$Al$$_2$$, in which the valence crossover plays important role for the heavy fermion superconductivity.

Journal Articles

Polarized neutron scattering study of the multiple order parameter system NdB$$_4$$

Metoki, Naoto; Yamauchi, Hiroki; Matsuda, Masaaki*; Fernandez-Baca, J. A.*; Watanuki, Ryuta*; Hagiwara, Masato*

Physical Review B, 97(17), p.174416_1 - 174416_10, 2018/05

 Times Cited Count:3 Percentile:24.8(Materials Science, Multidisciplinary)

Neutron polarization analysis has been carried out in order to clarify the magnetic structure of multiple order parameter $$f$$-electron system NdB$$_4$$. We confirmed the non-collinear "all-in all-out" structure ($$Gamma$$$$_{4}$$) of the in-plane moment. We found that the magnetic moment along the $$c$$-axis $$m_c$$ showed diagonally antiferromagnetic structure ($$Gamma_{10}$$). The unusual magnetic ordering is phenomenologically understood via Landau theory. We also found that a long-period incommensurate modulation of the ($$0,0,1/2$$) antiferromagnetic structure of $$m_c$$ with the propagation $$q_{s1}$$ = (0.14, 0.14, 0.1) and $$q_{s2}$$ = (0.2, 0, 0.1) in phase III and IV, respectively. It is clear that the multipole degree-of-freedom based on pseudo-quartet $$f$$-electron state play important role.

Journal Articles

Neutron scattering study of yttrium iron garnet

Shamoto, Shinichi; Ito, Takashi; Onishi, Hiroaki; Yamauchi, Hiroki; Inamura, Yasuhiro; Matsuura, Masato*; Akatsu, Mitsuhiro*; Kodama, Katsuaki; Nakao, Akiko*; Moyoshi, Taketo*; et al.

Physical Review B, 97(5), p.054429_1 - 054429_9, 2018/02

 Times Cited Count:10 Percentile:63.24(Materials Science, Multidisciplinary)

Nuclear and magnetic structure and full magnon dispersions of yttrium iron garnet Y$$_3$$Fe$$_5$$O$$_{12}$$ have been studied by neutron scattering. The lowest-energy dispersion below 14 meV exhibits a quadratic dispersion as expected from ferromagnetic magnons. The imaginary part of $$q$$-integrated dynamical spin susceptibility $$chi$$"($$E$$) exhibits a square-root energy-dependence in the low energies. The magnon density of state is estimated from the $$chi$$"($$E$$) obtained on an absolute scale. The value is consistent with a single chirality mode for the magnon branch expected theoretically.

Journal Articles

Magnetic structure and quadrupolar order parameter driven by geometrical frustration effect in NdB$$_4$$

Yamauchi, Hiroki; Metoki, Naoto; Watanuki, Ryuta*; Suzuki, Kazuya*; Fukazawa, Hiroshi; Chi, S.*; Fernandez-Baca, J. A.*

Journal of the Physical Society of Japan, 86(4), p.044705_1 - 044705_9, 2017/04

 Times Cited Count:7 Percentile:59.82(Physics, Multidisciplinary)

Neutron diffraction experiments have been carried out to characterize the magnetic structures and order parameters in an intermediate phase of NdB$$_4$$ showing the successive phase transitions at $$T_{rm 0} = 17.2$$ K, $$T_{rm N1} = 7.0$$ K, and $$T_{rm N2} = 4.8$$ K. The observed patterns in phase II ($$T_{rm N1} < T < T_{rm 0}$$) are successfully explained by postulating a planar structure with static magnetic moments in the tetragonal $$ab$$-plane. We have found that the magnetic structure in phase II can be uniquely determined to be a linear combination of noncolinear "all-in/all-out"-type and "vortex"-type antiferromagnetic structures. We propose that the quadrupolar interaction holds the key to stabilizing the noncollinear magnetic structure and quadrupolar order. Here, the frustration in the Shastry - Sutherland lattice would play an essential role in suppressing the dominance of the magnetic interaction.

Journal Articles

Neutron powder diffraction study on the magnetic structure of NdPd$$_5$$Al$$_2$$

Metoki, Naoto; Yamauchi, Hiroki; Kitazawa, Hideaki*; Suzuki, Hiroyuki*; Hagiwara, Masato*; Frontzek, M. D.*; Matsuda, Masaaki*; Fernandez-Baca, J. A.*

Journal of the Physical Society of Japan, 86(3), p.034710_1 - 034710_5, 2017/03

 Times Cited Count:8 Percentile:63.32(Physics, Multidisciplinary)

Magnetic structure of NdPd$$_5$$Al$$_2$$ has been studied by means of neutron powder diffraction. We observed remarkable magnetic reflections with the modulation vector $$q$$= (1/2 0 0) below the ordering temperature $$T_{rm N}$$ = 1.2 K. We found a collinear magnetic structure of Nd moment of 2.9(1) $${mu}_{rm B}$$ at 0.3 K parallel to the $$c$$-axis, where the ferromagnetically ordered $$a$$ planes stack with four Nd layer period of ++-- sequence along the $$a$$ direction with the distance between adjuscent Nd layers to be $$a/2$$. This is very similar to CePd$$_5$$Al$$_2$$ with $$q$$ = (0.23 0.23 0) and the Ce moment parallel to the $$c$$-axis. These structures with in-plane modulation $$q_{|}$$ is a consequence of the two dimensional nature of fermi surface topology in this family, coming from unique crystal structure with very long tetragonal unit cell and large distance $$>$$ 7${AA}$ between the rare earth layers separated by Al and two Pd layers.

Journal Articles

Neutron diffraction of ice and water in hydrogels

Sekine, Yurina; Kobayashi, Riki*; Chi, S.*; Fernandez-Baca, J. A.*; Suzuya, Kentaro; Fujisaki, Fumika*; Ikeda, Kazutaka*; Otomo, Toshiya*; Fukazawa, Tomoko*; Yamauchi, Hiroki; et al.

JPS Conference Proceedings (Internet), 8, p.033009_1 - 033009_6, 2015/09

Neutron diffraction profiles of low-D$$_{2}$$O-content poly-N,N,-dimethylacrylamide (PDMAA) hydrogels were measured from 100 to 300 K to investigate the structure and properties of water in hydrogels. A broad diffraction observed at temperatures lower than 220 K indicates the existence of amorphous ice in the hydrogels at low temperatures. During the heating process, diffraction peaks from ice crystals appear in the profiles. These peaks indicate that cubic ice and hexagonal ice exist at T $$geq$$ 220 K. We refined the structure parameters of these ices in the hydrogel, which indicate the existence of low-density ice in the hydrogel.

Journal Articles

Neutron diffraction of ice in hydrogels

Sekine, Yurina; Fukazawa, Tomoko*; Aizawa, Mamoru*; Kobayashi, Riki*; Chi, S.*; Fernandez-Baca, J. A.*; Yamauchi, Hiroki; Fukazawa, Hiroshi

Journal of Physical Chemistry B, 118(47), p.13453 - 13457, 2014/08

 Times Cited Count:1 Percentile:2.1(Chemistry, Physical)

Neutron diffraction patterns for deuterated poly-$$N$$,$$N$$,-dimethylacrylamide (PDMAA) hydrogels were measured from 10 to 300 K to investigate the structure and properties of water in the gels. Diffraction peaks observed below 250 K indicate the existence of ice in the hydrogels. Some diffraction peaks from the ice are at lower diffraction angles than those in ordinary hexagonal ice (Ih). These shifts in peaks indicate that the lattice constants of the $$a$$ and $$c$$ axes in the ice are about 0.29% and 0.3% higher than those in ice Ih, respectively. The results show that bulk low-density ice can exist in PDMAA hydrogels. The distortions in the lattice structure of ice imply significant interactions between water molecules and the surrounding polymer chains, which play an important role in the chemical and mechanical properties of the hydrogel.

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:12.72(Physics, Multidisciplinary)

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:9 Percentile:55.77(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

Magnons and electromagnons in a spin-lattice-coupled frustrated magnet CuFeO$$2$$ as seen via inelastic neutron scattering

Nakajima, Taro*; Suno, Azusa*; Mitsuda, Setsuo*; Terada, Noriki*; Kimura, Shojiro*; Kaneko, Koji; Yamauchi, Hiroki

Physical Review B, 84(18), p.184401_1 - 184401_7, 2011/11

 Times Cited Count:32 Percentile:79.37(Materials Science, Multidisciplinary)

Journal Articles

Neutron diffraction study on the Xe behavior in clathrate hydrate analyzed by Rietveld/maximum entropy method

Igawa, Naoki; Taguchi, Tomitsugu; Hoshikawa, Akinori*; Yamauchi, Hiroki; Birumachi, Atsushi; Ishii, Yoshinobu*

IOP Conference Series; Materials Science and Engineering, 18, p.022021_1 - 022021_4, 2011/05

The neutron scattering length density distributions of Xe deuterohydrate were analyzed by Rietveld and MEM analysis applied to neutron powder diffraction data to clarify the Xe behavior in the temperature range from 10 to 245 K. A spherical positive scattering length density attributed to the Xe atom was observed at the center of the small cage of the hydrate. On the other hand, an ellipsoid shaped scattering length density distribution at the center of the large cage was observed; the major axis of the ellipsoid scattering length density was directed toward the center of a hexagonal facet of the large cage. The distributions of the Xe atom in the both cages were almost the same at any temperature.

Journal Articles

Structure and properties of ferroelectric ice

Fukazawa, Hiroshi; Arakawa, Masashi*; Kagi, Hiroyuki; Yamauchi, Hiroki; Chakoumakos, B. C.*; Fernandez-Baca, J. A.*

Physics and Chemistry of Ice 2010, p.421 - 428, 2011/03

Whether or not ice in the universe exists as ferroelectric is a question that has attracted interest in astrophysics and physical chemistry, because long-range electrostatic forces, caused by the ferroelectricity, might be an important factor for materials evolution and hydrogen bonding. From neutron diffraction and scattering measurements, we have studied ice with impurities, such as potassium, sodium and lithium, that acted as a catalyst. Time-resolved diffraction experiments show that ferroelectric ice XI with hydrogen-ordered arrangement nucleates and grows with time for about 5 days. We found that the doped ice that has once been converted to ice XI is a stronger ferroelectric ice than that has never been converted. We also show the existence of the ferroelectric ice under high-pressure and its formation from compressed amorphous ice.

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