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Journal Articles

Multipole ordering in -electron systems

Kubo, Katsunori; Hotta, Takashi

Physica B; Condensed Matter, 378-380, p.1081 - 1082, 2006/05

https://doi.org/10.1016/j.physb.2006.01.428

Times Cited Count：4 Percentile：22.76(Physics, Condensed Matter)

In order to investigate multipole ordering in -electron systems from a microscopic viewpoint, we study the so-called models on three kinds of lattices, simple cubic (sc), bcc, and fcc, based on a - coupling scheme with -electron hopping integrals through bonding. From the model, we derive an effective model for each lattice structure by using the second-order perturbation theory with respect to . By further applying mean-field theory to the effective model, we find a $Gamma_{3g}$ antiferro-quadrupole transition for the sc lattice, a $Gamma_{2u}$ antiferro-octupole transition for the bcc lattice, and a longitudinal triple- $Gamma_{5u}$ octupole transition for the fcc lattice.

Journal Articles

Multipole ordering in -electron systems on the basis of a - coupling scheme

Kubo, Katsunori; Hotta, Takashi

Physical Review B, 72(14), p.144401_1 - 144401_12, 2005/10

https://doi.org/10.1103/PhysRevB.72.144401

Times Cited Count：30 Percentile：72.79(Materials Science, Multidisciplinary)

We investigate microscopic aspects of multipole ordering in -electron systems with emphasis on the effect of lattice structure. For the purpose, we construct -electron models on three kinds of lattices, simple cubic (sc), bcc, and fcc, in a tight-binding approximation on the basis of a - coupling scheme. Then, an effective model is derived in the strong-coupling limit for each lattice with the use of second-order perturbation theory with respect to . By applying mean-field theory to such effective models, we find multipole ordered states depending on the lattice structure. For the sc lattice, a $Gamma_{3g}$ antiferro-quadrupole transition occurs at a finite temperature and at further lowering temperature, we find another transition to a ferromagnetic state. For the bcc lattice, a $Gamma_{2u}$ antiferro-octupole ordering occurs first, and then, a ferromagnetic phase transition follows it. Finally, for the fcc lattice, we find a single phase transition to the longitudinal triple- $Gamma_{5u}$ octupole ordering.

Journal Articles

Analysis of - model for octupole ordering in NpO

Kubo, Katsunori; Hotta, Takashi

Physical Review B, 72(13), p.132411_1 - 132411_4, 2005/10

https://doi.org/10.1103/PhysRevB.72.132411

Times Cited Count：37 Percentile：77.56(Materials Science, Multidisciplinary)

In order to examine the origin of octupole ordering in NpO, we propose a microscopic model constituted of neptunium and oxygen orbitals. To study multipole ordering, we derive effective multipole interactions from the - model by using the fourth-order perturbation theory in terms of - hopping integrals. Analyzing the effective model numerically, we find a tendency toward $Gamma_{5u}$ antiferro-octupole ordering.

Journal Articles

Symmetry lowering in NpO; $^{17}$ O-NMR study

Tokunaga, Yo; Homma, Yoshiya*; Kambe, Shinsaku; Aoki, Dai*; Sakai, Hironori; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; Walstedt, R. E.; Yasuoka, Hiroshi

Physica B; Condensed Matter, 359-361, p.1096 - 1098, 2005/04

https://doi.org/10.1016/j.physb.2005.01.297

Times Cited Count：7 Percentile：33.79(Physics, Condensed Matter)

In order to elucidate the nature of the exotic ordered phase of NpO below = 26 K, we have initiated the first $^{17}$ O-NMR measurements. From the temperature dependence of the $^{17}$ O-NMR spectrum, the occurrence of two inequivalent oxygen sites has been confirmed below . This finding verifies the lowering of symmetry in the ordered state of NpO.

Journal Articles

NMR evidence for triple- multipole structure in NpO

Tokunaga, Yo; Homma, Yoshiya*; Kambe, Shinsaku; Aoki, Dai*; Sakai, Hironori; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; Walstedt, R. E.; Yasuoka, Hiroshi

Physical Review Letters, 94(13), p.137209_1 - 137209_4, 2005/04

https://doi.org/10.1103/PhysRevLett.94.137209

Times Cited Count：78 Percentile：90.09(Physics, Multidisciplinary)

In order to elucidate the nature of the exotic ordered phase of NpO below = 26 K, we have initiated the first $^{17}$ O-NMR measurements on this system. From the $^{17}$ O-NMR spectrum, the occurrence of two inequivalent oxygen sites has been confirmed below . It has also been shown that the characteristic features of the hyperfine interaction at the oxygen sites are well explained by invoking a hyperfine interaction with field-induced antiferromagnetic moments which appear as a result of the triple- antiferro-quadrupolar order. The NMR findings strongly support the occurrence of the longitudinal triple- multipole structure in NpO.

Journal Articles

Spin wave and orbital ordering in the C-type antiferromagnetic phase of Nd $_{1-x}$ Sr $_{x}$ MnO $_{3}$

Kajimoto, Ryoichi; Yoshizawa, Hideki*; Kawasaki, Ryuichi*; Noda, Kohei*; Kuwahara, Hideki*

Journal of the Physical Society of Japan, 74(1), p.502 - 503, 2005/01

https://doi.org/10.1143/JPSJ.74.502

Times Cited Count：2 Percentile：19.77(Physics, Multidisciplinary)

The spin wave dispersion relation of the C-type antiferromagnetic structure in Nd $_{0.25}$ Sr $_{0.75}$ MnO $_{3}$ was determined by neutron scattering. The spin exchange interactions show a large anisotropy, which evidences the d $_{3z^2-r^2}$ orbital ordering along the axis. The exchange interaction along the direction is fairly large and similar to the value in the ferromagnetic metallic phase, suggesting there is finite hopping of charges along the orbital chains.

Journal Articles

Long periodic magnetic structure in CeBC

Oyama, Kenji*; Kaneko, Koji; Onimaru, Takahiro*; Tobo, Aya*; Ishimoto, Kenichi*; Onodera, Hideya*; Yamaguchi, Yasuo*

Journal of the Physical Society of Japan, 72(12), p.3303 - 3304, 2003/12

https://doi.org/10.1143/JPSJ.72.3303

Times Cited Count：6 Percentile：43(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Single crystal growth and structural and magnetic properties of the uranium thernary intermetallic compound UCrSi

Matsuda, Tatsuma; Metoki, Naoto; Haga, Yoshinori; Ikeda, Shugo; Okubo, Tomoyuki*; Sugiyama, Kiyohiro*; Nakamura, Noriko*; Kindo, Koichi*; Kaneko, Koji; Nakamura, Akio; et al.

Journal of the Physical Society of Japan, 72(1), p.122 - 130, 2003/01

https://doi.org/10.1143/JPSJ.72.122

Times Cited Count：11 Percentile：57.14(Physics, Multidisciplinary)

no abstracts in English

JAEA Reports

Abstracts of the Workshop on Orbital Ordering and Fluctuations in d- and f-electron Systems; March 4-6, 2002, ASRC, JAERI, Tokai, Japan

Ueda, Kazuo; Hotta, Takashi

JAERI-Review 2002-037, 31 Pages, 2002/12

JAERI-Review-2002-037.pdf:2.7MB

Strongly correlated f- and d-electron systems including heavy Fermion systems and transition metal oxides are important source of exciting new phenomena in condensed matter physics. Recently it has been recognized in more profound way that the orbital degeneracy of the f- and d-electrons plays very important role underlying those exotic phenomena. The idea of the present workshop is to bring active researchers in the field together and to exchange ideas in informal atmosphere. In the workshop many interesting results were presented and stimulating discussions were made as clearly seen by the present report.

Journal Articles

Orbital ordering in manganites and ruthenates

Hotta, Takashi; Dagotto, E.*

Physica B; Condensed Matter, 312-313(1-4), p.700 - 702, 2002/03

https://doi.org/10.1016/S0921-4526(01)01491-0

Times Cited Count：2 Percentile：14.65(Physics, Condensed Matter)

The crucial role of the orbital degree of freedom is here discussed in order to understand the complex spin and charge structures of transition metal oxides. For manganites, it is shown that diagonal charge stripes in the ferromagnetic phase are induced by the staggered orbital ordered pattern, while for ruthenates, a novel orbital ordering is found to exist in the G-type antiferromagnetic structure, with a hole arrangement as recently observed in X-ray experiments.

Journal Articles

Prediction of orbital ordering in single-layered ruthenates

Hotta, Takashi; Dagotto, E.*

Physical Review Letters, 88(1), p.017201_1 - 017201_4, 2002/01

https://doi.org/10.1103/PhysRevLett.88.017201

Times Cited Count：80 Percentile：90(Physics, Multidisciplinary)

The key role of the orbital degree of freedom to understand the magnetic properties of layered ruthenates is here discussed. In the G-type antiferromagnetic (AFM) phase of CaRuO, recent X-ray experiments reported the presence of 0.5 hole per site in the $d_{rm xy}$ orbital, while the $d_{rm yz}$ and $d_{rm zx}$ orbitals contain 1.5 holes. This unexpected $t_{rm 2g}$ hole distribution is explained by a novel state with orbital ordering (OO), stabilized by a combination of Coulomb interactions and lattice distortions. In addition, the rich phase diagram presented here suggests the possibility of large magnetoresistance effects, and predicts a new ferromagnetic OO phase in ruthenates.