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Yamauchi, Hiroki; Metoki, Naoto; Watanuki, Ryuta*; Hong, T.*; Fernandez-Baca, J. A.*; Hagihara, Masato; Masuda, Takatsugu*; Yoshizawa, Hideki*; Ito, Shinichi*
Journal of the Physical Society of Japan, 94(5), p.054705_1 - 054705_8, 2025/04
Metoki, Naoto; Yamauchi, Hiroki; Hagihara, Masato; Watanuki, Ryuta*; Kawamura, Seiko; Kofu, Maiko*; Nakajima, Kenji; Matsuda, Masaaki*
Physical Review B, 111(10), p.104424_1 - 104424_9, 2025/03
Times Cited Count:0 Percentile:0.00(Materials Science, Multidisciplinary)Inelastic neutron scattering experiments were carried out to understand the unusual successive order in NdB with the frustrated Shatry-Sutherland (SS) lattice. The pseudo-quartet with
and
splits into four levels in the magnetically ordered states. The spectra can be explained with the on-site magnetic interaction
, the coupling of
with quadrupole
, and the uniaxial crystalline electric field. The
-electron states reproduce the temperature dependences of the in-plane moment
which is the primary order parameter, and a weakly induced
as the secondary order parameter. The magnetic-quadrupole coupling emerges and play essential role under the geometrical frustration, where the Heisenberg interactions are cancelled out.
Kofu, Maiko; Watanuki, Ryuta*; Sakakibara, Toshiro*; Kawamura, Seiko; Nakajima, Kenji; Matsuura, Masato*; Ueki, Takeshi*; Akutsu, Kazuhiro*; Yamamuro, Osamu*
Scientific Reports (Internet), 11(1), p.12098_1 - 12098_8, 2021/06
Times Cited Count:8 Percentile:58.52(Multidisciplinary Sciences)Metoki, Naoto; Yamauchi, Hiroki; Matsuda, Masaaki*; Fernandez-Baca, J. A.*; Watanuki, Ryuta*; Hagihara, Masato*
Physical Review B, 97(17), p.174416_1 - 174416_10, 2018/05
Times Cited Count:11 Percentile:43.92(Materials Science, Multidisciplinary)Neutron polarization analysis has been carried out in order to clarify the magnetic structure of multiple order parameter -electron system NdB
. We confirmed the non-collinear "all-in all-out" structure (
) of the in-plane moment. We found that the magnetic moment along the
-axis
showed diagonally antiferromagnetic structure (
). The unusual magnetic ordering is phenomenologically understood via Landau theory. We also found that a long-period incommensurate modulation of the (
) antiferromagnetic structure of
with the propagation
= (0.14, 0.14, 0.1) and
= (0.2, 0, 0.1) in phase III and IV, respectively. It is clear that the multipole degree-of-freedom based on pseudo-quartet
-electron state play important role.
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:19 Percentile:72.15(Physics, Multidisciplinary)Neutron diffraction experiments have been carried out to characterize the magnetic structures and order parameters in an intermediate phase of NdB showing the successive phase transitions at
K,
K, and
K. The observed patterns in phase II (
) are successfully explained by postulating a planar structure with static magnetic moments in the tetragonal
-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.
Mitamura, Hiroyuki*; Watanuki, Ryuta*; Kaneko, Koji; Sakakibara, Toshiro*
Kotai Butsuri, 50(12), p.821 - 832, 2015/12
no abstracts in English
Mitamura, Hiroyuki*; Watanuki, Ryuta*; Kaneko, Koji; Onozaki, Norimichi*; Amo, Yuta*; Kittaka, Shunichiro*; Kobayashi, Riki*; Shimura, Yasuyuki*; Yamamoto, Isao*; Suzuki, Kazuya*; et al.
Physical Review Letters, 113(14), p.147202_1 - 147202_5, 2014/10
Times Cited Count:27 Percentile:77.66(Physics, Multidisciplinary)Kobayashi, Riki; Kaneko, Koji; Wakimoto, Shuichi; Chi, S.*; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*
Journal of the Korean Physical Society, 63(3), p.337 - 340, 2013/08
Times Cited Count:5 Percentile:37.72(Physics, Multidisciplinary)Matsuo, Motoaki*; Saito, Hiroyuki; Machida, Akihiko; Sato, Ryutaro*; Takagi, Shigeyuki*; Miwa, Kazutoshi*; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi; Orimo, Shinichi*
RSC Advances (Internet), 3(4), p.1013 - 1016, 2013/01
Times Cited Count:20 Percentile:53.33(Chemistry, Multidisciplinary)Tokunaga, Yo; Saito, Yo*; Sakai, Hironori; Kambe, Shinsaku; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*; Kawasaki, Yu*; Kishimoto, Yutaka*
Physical Review B, 84(21), p.214403_1 - 214403_7, 2011/12
Times Cited Count:9 Percentile:37.64(Materials Science, Multidisciplinary)We report NMR studies of TbCoGa, which has the tetragonal HoCoGa
structure and exhibits two antiferromagnetic (AF) transitions at
=36.2 K and
=5.4 K. From a symmetry analysis of internal magnetic fields at orthorhombic Ga sites, we have successfully determined the magnetic structures in the AF-I (
) and AF-II (
) phases. The AF-I phase is a collinear AF order with a propagation vector
and ordered moments parallel to the [001] direction. In the AF-II phase, on the other hand, we found a non-collinear AF structure described by double propagation vectors
and
, where the moments tilt away from the [001] direction toward [100], keeping a constant value along the [001] direction. In the context of these results we discuss the possible presence of magnetic frustration in this system.
Yamauchi, Hiroki; Watanuki, Ryuta*; Chi, S.*; Fernandez-Baca, J. A.*; Kaneko, Koji; Kawasaki, Takuro; Kiyanagi, Ryoji; Hanashima, Takayasu*
no journal, ,
no abstracts in English
Metoki, Naoto; Yamauchi, Hiroki; Watanuki, Ryuta*; Suzuki, Kazuya*; Hagihara, Masato*; Masuda, Takatsugu*; Matsuda, Masaaki*; Songxue, C.*; Fernandez Baca, J.*
no journal, ,
Our neutron scattering study and using representational analysis revealed the magnetic structure in phase II of NdB with Shastry-Sutherland lattice. We found that the magnetic structure is described by the mixture of the basis vector of
and
representation with the magnetic moment of about 2
. We observed pseudo-quartet CEF state and the temperature dependence by means of neutron inelastic scattering below 5 meV.
Kofu, Maiko; Watanuki, Ryuta*; Sakakibara, Toshiro*; Kawamura, Seiko; Nakajima, Kenji; Ueki, Takeshi*; Akutsu, Kazuhiro*; Yamamuro, Osamu*
no journal, ,
Ionic liquids (ILs) have been in the spotlight due to their unique and interesting properties. It is remarkable that their physicochemical properties are controlled by varying cations and anions. Magnetic IL is an example. The first discovered magnetic IL CmimFeCl
is easily vitrified upon cooling and also crystallized by annealing. Interestingly, an antiferromagnetic transition occurs at 2.3 K in the crystalline state while spin-glass behavior is observed below 0.45 K (=
) in the glassy state. Our inelastic neutron scattering experiments have demonstrated that the glassy C
mimFeCl
exhibits a broad and non-dispersive excitation, while the crystal displays spin-wave excitations. The excitation spectrum in the glass state is scaled by the Bose population factor below
, which is highly reminiscent of "boson peak" commonly observed in structural glasses. We guess that, since there is no periodicity in structural glasses, magnons hardly propagate through magnetic medium and are localized.
Kofu, Maiko; Watanuki, Ryuta*; Sakakibara, Toshiro*; Kawamura, Seiko; Nakajima, Kenji; Ueki, Takeshi*; Akutsu, Kazuhiro*; Yamamuro, Osamu*
no journal, ,
Ionic liquids (ILs) have been in the spotlight due to their unique and interesting properties. It is remarkable that their physicochemical properties are controlled by varying cations and anions. Magnetic IL is an example. The first discovered magnetic IL CmimFeCl
is easily vitrified upon cooling and also crystallized by annealing. Interestingly, an antiferromagnetic transition occurs at 2.3 K in the crystalline state while spin-glass behavior is observed below 0.45 K (=
) in the glassy state. Our inelastic neutron scattering experiments have demonstrated that the glassy C
mimFeCl
exhibits a broad and non-dispersive excitation, while the crystal displays spin-wave excitations. The excitation spectrum in the glass state is scaled by the Bose population factor below
, which is highly reminiscent of "boson peak" commonly observed in structural glasses. Since there is no periodicity in structural glasses, magnons hardly propagate through magnetic medium and are localized. The localized magnetic excitations are suggestive of the formation of spin cluster.
Kofu, Maiko; Watanuki, Ryuta*; Sakakibara, Toshiro*; Kawamura, Seiko; Nakajima, Kenji; Ueki, Takeshi*; Akutsu, Kazuhiro*; Yamamuro, Osamu*
no journal, ,
Ionic liquids (ILs) have been in the spotlight due to their unique and interesting properties. It is remarkable that their physicochemical properties are controlled by varying cations and anions. Magnetic IL is an example. The first discovered magnetic IL CmimFeCl
is easily vitrified upon cooling and also crystallized by annealing. Interestingly, an antiferromagnetic transition occurs at 2.3 K in the crystalline state while spin-glass behavior is observed below 0.45 K (=
) in the glassy state. Our inelastic neutron scattering experiments have demonstrated that the glassy C
mimFeCl
exhibits a broad and non-dispersive excitation, while the crystal displays spin-wave excitations. The excitation spectrum in the glass state is scaled by the Bose population factor below
, which is highly reminiscent of "boson peak" commonly observed in structural glasses. We guess that, since there is no periodicity in structural glasses, magnons hardly propagate through magnetic medium and are localized. The localized magnetic excitations are suggestive of the formation of spin clusters.
Michimura, Shinji; Inami, Toshiya; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*
no journal, ,
no abstracts in English
Metoki, Naoto; Yamauchi, Hiroki; Watanuki, Ryuta*; Kawamura, Seiko; Yoshida, Masahiro*; Yoshizawa, Hideki*
no journal, ,
NdB has a crystal structure with two-dimensional orthogonal dimers that are expected to be geometrically frustrated. In the magnetic ordered phase, magnetic moment has a complex structure in which orthogonal in-plane components and a weak c-axis component are induced. To clarify the ordering mechanism and order parameter, we focused on the
electronic state and carried out inelastic neutron scattering experiments on this system. In the paramagnetic state, we found a quasi-doublet state associated with a strong uniaxial crystal field, which can be explained by the entropy released with successive transitions. In addition, in the ordered phase, a peak shift and splitting into four singlets were observed. We analyzed the temperature dependence of the spectrum considering with magnetic and quadrupolar interactions and their coupling terms. The results can well explain the mechanism of the transition, which we will show in this presentation.
Kaneko, Koji; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*; Osakabe, Toyotaka
no journal, ,
no abstracts in English
Tokunaga, Yo; Saito, Yo*; Sakai, Hironori; Kambe, Shinsaku; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*; Kawasaki, Yu*; Kishimoto, Yutaka*
no journal, ,
We report NMR studies of TbCoGa, which has the tetragonal HoCoGa
structure and exhibits two antiferromagnetic (AF) transitions at
=36.2 K and
=5.4 K. From analysis of the internal fields at Ga sites, we have determined the magnetic structures of the AF-I (
) and the AF-II (
) phases. The AF-I phase is a collinear AF order with the propagation vector q=[1/2, 0, 1/2] and with ordered moments parallel to the c axis. This is in accordance with the neutron diffraction measurements. In the AF-II phase, on the other hand, we found a non-collinear AF structure described with double propagation vectors
=[1/2, 0, 1/2] and
=[0, 1/2, 1/2]. Interestingly, the NMR reveals that the c component of the Tb moments does not change value between the AF-I and the AF-II phases, even though an a component is newly developed in the AF-II phase.
Kaneko, Koji; Wakimoto, Shuichi; Chi, S.*; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*; Kobayashi, Riki
no journal, ,
no abstracts in English