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Journal Articles

Neutron spectroscopy study on crystalline electric field excitations in NdB$$_4$$

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

https://doi.org/10.7566/JPSJ.94.054705

Journal Articles

Magnetic and quadrupole coupling emerging in NdB$$_4$$ with geometrically frustrated orthogonal antiferromagnetic dimer

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

https://doi.org/10.1103/PhysRevB.111.104424
 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$$_4$$ with the frustrated Shatry-Sutherland (SS) lattice. The pseudo-quartet with $$|pm frac{5}{2}rangle$$ and $$|pm frac{7}{2}rangle$$ splits into four levels in the magnetically ordered states. The spectra can be explained with the on-site magnetic interaction $$langle J_x rangle J_x$$, the coupling of $$J_x$$ with quadrupole $$O_{zx}$$, and the uniaxial crystalline electric field. The $$f$$-electron states reproduce the temperature dependences of the in-plane moment $$m_perp=langle J_x rangle$$ which is the primary order parameter, and a weakly induced $$m_c=langle J_z rangle$$ 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.

Journal Articles

Spin glass behavior and magnetic boson peak in a structural glass of a magnetic ionic liquid

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

https://doi.org/10.1038/s41598-021-91619-z
 Times Cited Count：8 Percentile：58.52(Multidisciplinary Sciences)

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*; Hagihara, Masato*

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

https://doi.org/10.1103/PhysRevB.97.174416
 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 $$f$$-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

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

https://doi.org/10.7566/JPSJ.86.044705
 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$$_4$$ 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

The Spin chirality and ferroelectricity on a triangular lattice antiferromagnet

Mitamura, Hiroyuki*; Watanuki, Ryuta*; Kaneko, Koji; Sakakibara, Toshiro*

Kotai Butsuri, 50(12), p.821 - 832, 2015/12

no abstracts in English

Journal Articles

Spin-chirality-driven ferroelectricity on a perfect triangular lattice antiferromagnet

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

https://doi.org/10.1103/PhysRevLett.113.147202
 Times Cited Count：27 Percentile：77.66(Physics, Multidisciplinary)

Journal Articles

Powder neutron diffraction study of HoCoGa$$_{5}$$

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

https://doi.org/10.3938/jkps.63.337
 Times Cited Count：5 Percentile：37.72(Physics, Multidisciplinary)

Journal Articles

Formation of an Fe-H complex anion in YFe$$_{2}$$; Adjustment of imbalanced charge by additional Li as an electron donor

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

https://doi.org/10.1039/c2ra22497f
 Times Cited Count：20 Percentile：53.33(Chemistry, Multidisciplinary)

Journal Articles

NMR determination of noncollinear antiferromagnetic structure in TbCoGa$$_5$$

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

https://doi.org/10.1103/PhysRevB.84.214403
 Times Cited Count：9 Percentile：37.64(Materials Science, Multidisciplinary)

We report NMR studies of TbCoGa$$_5$$, which has the tetragonal HoCoGa$$_5$$ structure and exhibits two antiferromagnetic (AF) transitions at $$T_{rm N1}$$=36.2 K and $$T_{rm N2}$$=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 ($$T_{rm N2}<T<T_{rm N1}$$) and AF-II ($$T<T_{rm N2}$$) phases. The AF-I phase is a collinear AF order with a propagation vector $$q=[1/2, 0, 1/2]$$ 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 $$q_1=[1/2, 0, 1/2]$$ and $$q_{2}=[0, 1/2, 1/2]$$, 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.

Oral presentation

Neutron scattering studies on multi-phase transitions in NdB$$_4$$

Yamauchi, Hiroki; Watanuki, Ryuta*; Chi, S.*; Fernandez-Baca, J. A.*; Kaneko, Koji; Kawasaki, Takuro; Kiyanagi, Ryoji; Hanashima, Takayasu*

no journal, , 

no abstracts in English

Oral presentation

Neutron scattering study on NdB$$_4$$

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$$_4$$ with Shastry-Sutherland lattice. We found that the magnetic structure is described by the mixture of the basis vector of $$Gamma_2$$ and $$Gamma_4$$ representation with the magnetic moment of about 2$$mu_B$$. We observed pseudo-quartet CEF state and the temperature dependence by means of neutron inelastic scattering below 5 meV.

Oral presentation

Neutron scattering study of a magnetic ionic liquid C$$_{4}$$mimFeCl$$_{4}$$

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 C$$_{4}$$mimFeCl$$_{4}$$ 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 (= $$T_{rm SG}$$) in the glassy state. Our inelastic neutron scattering experiments have demonstrated that the glassy C$$_{4}$$mimFeCl$$_{4}$$ 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 $$T_{rm SG}$$, 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.

Oral presentation

Spin glass on a structural glass of a magnetic ionic liquid

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 C$$_{4}$$mimFeCl$$_{4}$$ 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 (= $$T_{rm SG}$$) in the glassy state. Our inelastic neutron scattering experiments have demonstrated that the glassy C$$_{4}$$mimFeCl$$_{4}$$ 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 $$T_{rm SG}$$, 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.

Oral presentation

Spin glass dynamics in a structural glass of C$$_{4}$$mimFeCl$$_{4}$$

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 C$$_{4}$$mimFeCl$$_{4}$$ 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 (= $$T_{rm SG}$$) in the glassy state. Our inelastic neutron scattering experiments have demonstrated that the glassy C$$_{4}$$mimFeCl$$_{4}$$ 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 $$T_{rm SG}$$, 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.

Oral presentation

Resonant X-ray diffraction study of successive magnetic orderings of rectangular components in TbCoGa$$_5$$

Michimura, Shinji; Inami, Toshiya; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*

no journal, , 

no abstracts in English

Oral presentation

$$f$$-electron states in NdB$$_4$$

Metoki, Naoto; Yamauchi, Hiroki; Watanuki, Ryuta*; Kawamura, Seiko; Yoshida, Masahiro*; Yoshizawa, Hideki*

no journal, , 

NdB$$_4$$ 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 $$f$$ 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.

Oral presentation

Neutron scattering study on successive transitions in TbCoGa$$_5$$

Kaneko, Koji; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*; Osakabe, Toyotaka

no journal, , 

no abstracts in English

Oral presentation

Non-collinear antiferromagnetic structure in TbCoGa$$_5$$

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$$_5$$, which has the tetragonal HoCoGa$$_5$$ structure and exhibits two antiferromagnetic (AF) transitions at $$T_{N1}$$=36.2 K and $$T_{N2}$$=5.4 K. From analysis of the internal fields at Ga sites, we have determined the magnetic structures of the AF-I ($$T_{N2}<T<T_{N1}$$) and the AF-II ($$T<T_{N2}$$) 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 $$q_1$$=[1/2, 0, 1/2] and $$q_2$$=[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.

Oral presentation

Magnetic structure of RCoGa$$_5$$ (R=Tb, Ho)

Kaneko, Koji; Wakimoto, Shuichi; Chi, S.*; Sanada, Naoyuki*; Watanuki, Ryuta*; Suzuki, Kazuya*; Kobayashi, Riki

no journal, , 

no abstracts in English

26 (Records 1-20 displayed on this page)