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Journal Articles

$$f$$-electron states of NpPd$$_5$$Al$$_2$$ and the isostructural family; Heavy fermion superconductivity accompanied by valence crossover

Metoki, Naoto

Kotai Butsuri, 55(7), p.285 - 296, 2020/07

Electron states are the main theme of "solid-state physics", which is essential for microscopic understanding of multipoles and superconductivity, etc. 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

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

Pseudo-triplet 5$$f$$ electron state in the heavy fermion superconductor NpPd$$_5$$Al$$_2$$

Metoki, Naoto; Aoki, Dai*; Griveau, J.-C.*; Otsuki, Junya*

Journal of the Physical Society of Japan, 89(2), p.024707_1 - 024707_6, 2020/02

 Times Cited Count:2 Percentile:51.78(Physics, Multidisciplinary)

The pseudo triplet ground state in the heavy-fermion superconductor NpPd$$_5$$Al$$_2$$ was concluded. The magnetic susceptibility $$chi$$ can be reproduced by the singlet ground state $$Gamma_{t1}$$ with the main component of $$|0rangle$$ and the first excited doublet $$Gamma_{t5}$$ dominated by $$|pm1rangle$$ at $$Delta E=49$$,K. The magnetization curve can be explained from the effective local hamiltonian for pseudo spin $$J$$=1 with $$DJ_z^2$$($$D=Delta E$$) equivalent to the quadrupole operator $$O_{20}$$. The specific heat can be described with the Kondo model normalized to give the entropy R$$ln3$$, corresponding to the pseudo triplet state. The derived Kondo temperature $$T_{rm K}=55$$,K comparable to the level splitting $$Delta E=49$$,K indicates the contribution of the excited doublet $$Gamma_{t5}$$ to the possible multi-channel Kondo effect.

Journal Articles

$$f$$-electron states of heavy-fermion superconductor NpPd$$_5$$Al$$_2$$ and rare-earth- and actinide-based isostructural compounds

Metoki, Naoto

Journal of the Physical Society of Japan, 89(2), p.025001_1 - 025001_2, 2020/02

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

Good correspondence of the $$LS$$ and $$j$$-$$j$$ coupling scheme can be realized in the $$f$$-electron states of the heavy-fermion superconductor NpPd$$_5$$Al$$_2$$ and the isostructural family. The rare-earth and actinide elements are under a common strong uniaxial point charge potential with tetragonal point symmetry $$D_{4h}$$. The systematic development of the $$f$$-electron states can be understood in the $$LS$$ coupling scheme of $$^nf$$ configuration (the number of $$f$$ electrons $$nleq6$$). We can find the corresponding states in $$j$$-$$j$$ coupling scheme with three $$f$$-orbitals $$Gamma_7^{rm; i}, Gamma_7^{rm; ii}$$, and $$Gamma_6$$ determined from CePd$$_5$$Al$$_2$$ with $$^1f$$ configuration.

Journal Articles

Localized 5$$f^2$$ states in UPd$$_5$$Al$$_2$$ and valence crossover in the Vicinity of Heavy-Fermion superconductivity

Metoki, Naoto; Haga, Yoshinori; Yamamoto, Etsuji; Matsuda, Masaaki*

Journal of the Physical Society of Japan, 87(11), p.114712_1 - 114712_9, 2018/11

 Times Cited Count:2 Percentile:29.78(Physics, Multidisciplinary)

The localized 5$$f$$ states with 5$$f^2$$ ($$^3H_4$$) configuration of U$$^{4+}$$ ion have been revealed in UPd$$_5$$Al$$_2$$. We found that the low-lying states are the same as PrPd$$_5$$Al$$_2$$ flat orbitals with large $$J_z$$ are stabilized by a two-dimensional CEF potential in the unique crystal structure. The present study involves the valence crossover from tetravalent to trivalent in a series of AnPd$$_5$$Al$$_2$$, demonstrated by lattice and/or transport anomaly as well as many body effects in the vicinity of the boundary. The valence instability plays important role for the unusual heavy fermion superconductivity in NpPd$$_5$$Al$$_2$$.

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

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

Spin polarized neutron scattering study on metal-insulator crossover in uranium dichalcogenide $$beta$$-US$$_{2}$$

Metoki, Naoto; Sakai, Hironori; Suzuki, Michito; Yamamoto, Etsuji; Haga, Yoshinori; Matsuda, Tatsuma; Ikeda, Shugo*

JPS Conference Proceedings (Internet), 3, p.013011_1 - 013011_6, 2014/06

Uranium chalcogenides are highly interesting because of the variety of the physical properties from 5$$f$$-based metal and Mott-Hibbard insulator. Especially dichalcogenide family exhibits a metal-insulator crossover depending on the chalcogenide elements, or under magnetic field and pressure. In this talk we present a recent result of our neutron scattering study on uranium dichalcogenide, which demonstrates that the metal-insulator crossover is related to the change of 5$$f$$ character from localized to itinerant. The electronic structure related to this phenomenon is discussed based on the band calculation.

Journal Articles

Metal-insulator crossover accompanied by the dual nature of 5$$f$$ electrons with localized and itinerant charancters in $$beta$$-US$$_2$$

Metoki, Naoto; Sakai, Hironori; Yamamoto, Etsuji; Haga, Yoshinori; Matsuda, Tatsuma; Ikeda, Shugo*

Journal of the Korean Physical Society, 62(12), p.1782 - 1786, 2013/06

 Times Cited Count:1 Percentile:12.72(Physics, Multidisciplinary)

Magnetic excitation of a narrow gap semiconductor $$beta$$-US$$_2$$was studied by means of neutron scattering. At low temperatures clear crystalline electric field (CEF) excitations were observed, indicating localized character of 5$$f$$ electrons. The excitation energy $$sim$$7 meV of the pseudo doublet state is consistent with the level scheme based on 5$$f^2$$ configuration of U$$^ {4+}$$ ions, which reproduces the magnetic susceptibility, magnetization, and specific heat. With elevating temperature the conductivity recovers with 5$$f$$ carriers excited beyond the gap of 90 K. Simultaneously the CEF excitation becomes weak and broad, and is replaced by a quasi-elastic response of magnetic origin, indicating the crossover of 5$$f$$ character from localized to itinerant.

Journal Articles

Magnetic and nonmagnetic impurity effect on magnetic orderings of the isosceles-triangular-lattice antiferromagnet CuMnO$$_2$$

Terada, Noriki*; Tsuchiya, Yoshinori*; Kitazawa, Hideaki*; Metoki, Naoto

Journal of the Korean Physical Society, 62(12), p.1905 - 1909, 2013/06

 Times Cited Count:2 Percentile:22.1(Physics, Multidisciplinary)

We have investigated magnetic and nonmagnetic impurity substitution effects on magnetic ordering of a frustrated isosceles triangular lattice antiferromagnet CuMnO$$_2$$ by means of the magnetic neutron diffraction measurements on Cu(Mn$$_{1-y}$$Ga$$_y$$)O$$_2$$. While the magnetic wave vector of the magnetic ground state of "magnetically" substituted Cu(Mn$$_{1-x}$$Cu$$_x$$)O$$_2$$ with x = 0:04 is Q = (-1/2 1/2 0), that in the "nonmagnetically" substituted Cu(Mn$$_{1-y}$$Ga$$_y$$)O$$_2$$ with y =0.05, 0.15 and 0.20 is Q = (-1/2 1/2 1/2) that is identical to that of pure CuMnO$$_2$$. We discuss an influence of magnetic or nonmagnetic impurity substitution on the magnetic ordering of CuMnO$$_2$$, by comparing the results of Cu(Mn$$_{1-y}$$Ga$$_y$$)O$$_2$$ with Cu(Mn$$_{1-x}$$Cux)O$$_2$$.

Journal Articles

Neutron scattering experiments for the study of in-plane ordered moment in URu$$_2$$Si$$_2$$

Metoki, Naoto; Sakai, Hironori; Yamamoto, Etsuji; Tateiwa, Naoyuki; Matsuda, Tatsuma; Haga, Yoshinori

Journal of the Physical Society of Japan, 82(5), p.055004_1 - 055004_2, 2013/05

 Times Cited Count:17 Percentile:71.77(Physics, Multidisciplinary)

The hidden order parameter in URu$$_2$$Si$$_2$$ remains an open question for this quarter of a century. Many type of models have been proposed. The models predict unusual order parameters such as higher order multipole, dynamical origin, or very recently, "hastatic" order, accompanying Ising quasi-particles. We provide neutron scattering data measured at the wave vector $$Q$$=(003) for the in-plane magnetic component. The existence of the in-plane component in the order of $$sim$$0.01 or 10$$^{-2}$$$$sim$$10$$^{-3}$$ Bohr magneton has been proposed by a recent theoretical studies. The data were obtained also under magnetic field up to 10 T along the [010] direction in order to reveal a possible $$O_{xy}$$ type antiferro-quadrupole (AFQ) order at the propagation of $$Q$$=(001) proposed previously. Our data indicate that there is no in-plane magnetic component within the experimental accuracy of 0.004 Bohr magneton. Namely we could not obtain the results which support these theories.

Journal Articles

Neutron scattering study on high-quality single crystals of non-centrosymmetric heavy-fermion superconductor CePt$$_{3}$$Si

Kaneko, Koji; Stockert, O.*; Skoulatos, M.*; Schneidewind, A.*; Takeuchi, Tetsuya*; Matsuda, Tatsuma; Haga, Yoshinori; Settai, Rikio*; Onuki, Yoshichika; Metoki, Naoto

Journal of the Physical Society of Japan, 81(Suppl.B), p.SB006_1 - SB006_7, 2012/12

 Times Cited Count:2 Percentile:21.1(Physics, Multidisciplinary)

Journal Articles

Three-dimensional magnetically-oriented microcrystal array; A Large sample for neutron diffraction analysis

Kimura, Tsunehisa*; Kimura, Fumiko*; Matsumoto, Kenji*; Metoki, Naoto

Neutron Diffraction, p.179 - 202, 2012/03

We report the results of the neutron scattering study on three dimensionally oriented pseudo single crystals under rotating magnetic field.

Journal Articles

Report of the International Conference on Research Reactors; Safe Management and Effective Utilization

Metoki, Naoto

Hamon, 22(1), p.93 - 95, 2012/02

The International Conference on Research Reactors: Safe Management and Effective Utilization was Held in Rabat, the capital of the Kingdom of Morocco organized by IAEA hosted by the Kingdom of Morocco. Japan Atomic Energy Agency presented an invited talk about the (1) impact of the earthquake, (2) recent results, and (3) complementary research reactors and pulse neutron source. The talk was quoted in the summary talk which summarized as, "JRR-3 remains useful after J-PARC has been started. This and the construction of new research reactors, HANARO, OPAL FRM-II demonstrate an important role of the research reactors in the field of neutron science.", "JRR-3 has no serious damage from the earthquake, and the users look forward to an early re-operation."

Journal Articles

Neutron scattering studies of the spin-5/2 antiferromagnetic linear trimer substance SrMn$$_3$$P$$_4$$O$$_{14}$$

Hase, Masashi*; D$"o$nni, A.*; Ozawa, Kiyoshi*; Kitazawa, Hideaki*; Sakai, Osamu*; Pomjakushin, V. Y.*; Keller, L.*; Kaneko, Koji; Metoki, Naoto; Kakurai, Kazuhisa; et al.

Journal of Physics; Conference Series, 340, p.012066_1 - 012066_7, 2012/00

 Times Cited Count:1 Percentile:46.98

We determined the magnetic structure below $$T_{rm N1}=2.2(1)$$ K of the spin-5/2 antiferromagnetic (AF) trimer substance SrMn$$_3$$P$$_4$$O$$_{14}$$ using neutron powder diffraction experiments. The incommensurate propagation vector is expressed as [0, $$k_y$$, 0], due to competition between the nearest-neighbor and next-nearest-neighbor interactions in trimerized chains. The value of $$k_y$$ is 0.316 to 0.331, changing rapidly at $$T_{rm N2}= 1.75(5)$$ K. We confirmed that the intra-trimer $$J_1$$ interaction is AF. The magnetic excitation peaks were obsereved at 0.46, 0.68, and 1.02 meV. The weak Q dependence indicates the discrete energy levels, which do not contradict the AF trimer model with the intra-trimer interaction value of 0.29 meV (3.4 K).

Journal Articles

Magnetic excitations in the spin-5/2 antiferromagnetic trimer substance SrMn$$_3$$P$$_4$$O$$_{14}$$

Hase, Masashi*; Matsuda, Masaaki*; Kaneko, Koji; Metoki, Naoto; Kakurai, Kazuhisa; Yang, T.*; Cong, R.*; Lin, J.*; Ozawa, Kiyoshi*; Kitazawa, Hideaki*

Physical Review B, 84(21), p.214402_1 - 214402_6, 2011/12

 Times Cited Count:9 Percentile:42.37(Materials Science, Multidisciplinary)

Journal Articles

Spin density wave in insulating ferromagnetic frustrated chain LiCuVO$$_{4}$$

Masuda, Takatsugu*; Hagiwara, Masato*; Kondo, Yosuke*; Kaneko, Koji; Metoki, Naoto

Journal of the Physical Society of Japan, 80(11), p.113705_1 - 113705_4, 2011/11

 Times Cited Count:34 Percentile:83.07(Physics, Multidisciplinary)

We study a field-induced quantum phase in the weakly-coupled ferromagnetic frustrated chain LiCuVO$$_{4}$$ by a neutron diffraction technique. A new incommensurate magnetic peak is observed at H $$geq$$ 8.5 T. The field-dependent propagation vector is identified with the spin density wave correlation in the theoretically predicted magnetic quadrupole order. Quantum fluctuation, geometrical frustration, and interchain interaction induce an exotic spin density wave long-range order in the insulating magnet.

226 (Records 1-20 displayed on this page)