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Journal Articles

Magnetic structure determination of Ce$$T_{2}$$Al$$_{10}$$ ($$T$$ = Ru and Os); Single crystal neutron diffraction studies

Kato, Harukazu*; Kobayashi, Riki; Takesaka, Tomoaki*; Nishioka, Takashi*; Matsumura, Masahiro*; Kaneko, Koji; Metoki, Naoto

Journal of the Physical Society of Japan, 80(7), p.073701_1 - 073701_4, 2011/07

https://doi.org/10.1143/JPSJ.80.073701
 Times Cited Count：61 Percentile：89.36(Physics, Multidisciplinary)

Journal Articles

A Cu NQR study in a $$d$$-electron heavy-fermion system, CaCu$$_{3}$$Ru$$_{4}$$O$$_{12}$$

Kato, Harukazu*; Tsuruta, Takuya*; Nishioka, Takashi*; Matsumura, Masahiro*; Sakai, Hironori; Kambe, Shinsaku

Journal of Physics and Chemistry of Solids, 68(11), p.2187 - 2190, 2007/11

https://doi.org/10.1016/j.jpcs.2007.08.038
 Times Cited Count：8 Percentile：38.69(Chemistry, Multidisciplinary)

Cu nuclear quadrupole resonance (NQR) studies have been carried out for CaCu$$_{3}$$Ru$$_{4}$$O$$_{12}$$,which has been suggested to show a heavy-fermion-like behavioral though it possess no f electron. A Lorentzian shape of the Cu NQR line with a narrow width implies that no magnetic ordering appears, at least, down to 5 K. The spin-lattice relaxation rate of the Cu nuclei probes a change of the Cu 3$$d$$ electron nature, resulting in the Fermi liquid state at a low temperature. These facts strongly support that the heavy fermion picture is available in the concerned compound.

Journal Articles

NMR study of the semimetallic compound UCoGa$$_5$$

Kambe, Shinsaku; Sakai, Hironori; Kato, Harukazu*; Tokunaga, Yo; Fujimoto, Tatsuya*; Walstedt, R. E.*; Ikeda, Shugo; Maehira, Takahiro*; Haga, Yoshinori; Onuki, Yoshichika

Physical Review B, 76(2), p.024411_1 - 024411_6, 2007/07

https://doi.org/10.1103/PhysRevB.76.024411
 Times Cited Count：6 Percentile：31.31(Materials Science, Multidisciplinary)

We report NMR studies on a single crystal of UCoGa$$_5$$, which has the same tetragonal HoCoGa$$_5$$ (115) structure as the$$d$$-wave high-$$T_c$$ superconductor PuCoGa$$_5$$. The spin-lattice relaxation rate ($$1/T_1$$) in UCoGa$$_5$$ issmall comparing with those of other actinide 115 compounds. This fact is consistent with a semi-metallic nature of UCoGa$$_5$$ suggested by de Haas-van Alphen effect measurements and band calculations. From comparison of $$1/T_1$$ at crystallografically different Ga and Co sites and the static susceptibility, an existence of two bands with rather different characters is revealed.

Journal Articles

NMR study of magnetic fluctuations in 115 actinide compounds

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Kato, Harukazu; Fujimoto, Tatsuya; Walstedt, R. E.*; Ikeda, Shugo; Matsuda, Tatsuma; Haga, Yoshinori; Aoki, Dai*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.176 - 181, 2007/03

performed NMR measurements in 5f-115 compounds with various ground states [UFeGa$$_{5}$$ (Paramagnet), UPtGa$$_{5}$$, NpCoGa$$_{5}$$, NpFeGa$$_{5}$$ (Antiferromagnet) and PuRhGa$$_{5}$$ (Superconductor)], and evaluated the T-dependence of the local (actinide site) magnetic fluctuation energies (//c and c) in the paramagnetic states. An anisotropy in the magnetic fluctuations is observed in all compounds due to the strong LS coupling, in contrast to 3d-high Tc cuprates which have isotropic magnetic fluctuations at Cu sites. It is remarkable that the XY-type magnetic anisotropy is strong in PuRhGa$$_{5}$$ comparing with the non-superconducting 5f-115 compounds. The fluctuation energy in PuRhGa$$_{5}$$ is of the order of 10meV which is between of heavy fermion superconductors (1meV for $$T$$$$_{rm c}$$1K) and high $$T$$$$_{rm c}$$ cuprates (102meV for $$T$$$$_{rm c}$$100K). The relation between the magnetic fluctuation properties and the ground states will be discussed.

Journal Articles

Cu NMR study in a heavy-electron system, CaCu$$_3$$Ru$$_4$$O$$_{12}$$

Kato, Harukazu*; Tsuruta, Takuya*; Nishioka, Takashi*; Matsumura, Masahiro*; Sakai, Hironori; Kambe, Shinsaku

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.251 - 253, 2007/03

Cu NMR measurements have been carried out for CaCu$$_3$$Ru$$_4$$O$$_{12}$$, which shows a heavy-fermion-like behavior although it posseses no f electron moment. The field-sweep spectrum observed can be understood as a powder pattern of a Cu nucleus affected by the quadrupole interaction with no axial symmetry. The quadrupole parameters and the Knight shift of Cu are evaluated.

Journal Articles

NMR study of antiferromagnet UPtGa$$_{5}$$

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Fujimoto, Tatsuya; Kato, Harukazu; Walstedt, R. E.; Ikeda, Shugo; Matsuda, Tatsuma; Haga, Yoshinori; Onuki, Yoshichika

Journal of the Physical Society of Japan, 75(Suppl.), p.127 - 129, 2006/08

Recently, new superconductors have been discovered in Pu-based HoCoGa$$_5$$(115) structure compounds: PuCoGa$$_5$$ ($$T_{c}=18K$$) and PuRhGa$$_5$$ ($$T_{c}=9K$$). The discovery has stimulated a lot of interest in actinide compounds. We report NMR measurements on a high-quality single crystal sample of the non-superconducting U- and Np-based 115 compounds. In order to elucidate universal magnetic properties and the origin of superconductivity in the 115 families, spin-lattice relaxation and Knight shift measurements have been performed systematically in the non-superconducting 115 compounds. Comparison of dynamical properties with the superconducting Pu115 compounds will be presented.

Journal Articles

NMR studies of actinide compounds; The NMR of actinide nuclei

Walstedt, R. E.*; Tokunaga, Yo; Kato, Harukazu*; Sakai, Hironori; Fujimoto, Tatsuya; Kambe, Shinsaku; Yasuoka, Hiroshi

Journal of the Physical Society of Japan, 75(Suppl.), p.77 - 81, 2006/08

In a brief recap of recent work on actinide NMR studies at JAERI, we review the direct observation of $$^{235}$$U NMR which has been carried out for both UO$$_2$$ and USb$$_2$$, as well as the estimate of $$T_1$$(T) for $$^{235}$$U which has been obtained from indirect (i.e., $$T_2$$ of $$^{103}$$Rh) NMR studies of the Pauli paramagnet URh$$_3$$. New data for 1/$$T_1$$ vs. T for $$^{17}$$O in NpO$$_2$$ are presented and analyzed. A sizeable fraction of the observed relaxation rate is strongly field-dependent, an effect attributed to a cross-relaxation process from the 100%-abundant, I = 5/2 $$^{237}$$Np nuclear spins. Analysis of this relaxation component leads to quantitative estimates of $$T_{1Np}$$ (40ns) and of anomalously enhanced values of the $$^{17}$$O-$$^{237}$$Np nuclear spin-spin coupling. These effects as well as future prospects for actinide NMR studies are discussed.

Journal Articles

$$^{31}$$P-NMR study of the uranium-based filled skutterudite compound UFe$$_4$$P$$_{12}$$

Tokunaga, Yo; Matsuda, Tatsuma; Sakai, Hironori; Kato, Harukazu*; Kambe, Shinsaku; Walstedt, R. E.; Haga, Yoshinori; Onuki, Yoshichika; Yasuoka, Hiroshi

Physical Review B, 71(4), p.045124_1 - 045124_5, 2005/01

https://doi.org/10.1103/PhysRevB.71.045124
 Times Cited Count：10 Percentile：42.74(Materials Science, Multidisciplinary)

$$^{31}$$P NMR measurements have been performed on the uranium-based ferromagnetic insulator UFe$$_4$$P$$_{12}$$ with $$T_C= 3.15$$ K. The field-orientation dependence of the hyperfine interaction has been measured using a single crystal, and the results compared with a point-dipolar field calculation assuming local moments at the U sites. We have also measured the field and temperature dependence of the nuclear spin-lattice relaxation rate ($$1/T_1$$) in several fields between 1.0 and 5.5 T at temperatures between 1.4 and 300 K. The results are discussed on the basis of a localized picture for the uranium 5f electrons.

Journal Articles

Direct observation of $$^{235}$$U NMR in an itinerant 5${it f}$ electron system, USb$$_{2}$$

Kato, Harukazu*; Sakai, Hironori; Ikushima, Kenji*; Kambe, Shinsaku; Tokunaga, Yo; Aoki, Dai*; Haga, Yoshinori; Onuki, Yoshichika; Yasuoka, Hiroshi; Walstedt, R. E.

Journal of the Physical Society of Japan, 73(8), p.2085 - 2088, 2004/08

https://doi.org/10.1143/JPSJ.73.2085
 Times Cited Count：12 Percentile：57.62(Physics, Multidisciplinary)

Diret AFNMR studies of $$^{235}$$U, $$^{121}$$Sb and $$^{123}$$Sb nuclear spins have been carried out in the antiferromagnetic state of USb$$_{2}$$. The central $$^{235}$$U transition have been found as 217.2MHz based on several tests. The $$^{235}$$U hyperfine coupling constant is estimated as 147T/mB. This is the first observation of $$^{235}$$U NMR in a metallic compound.

Journal Articles

Magnetism of uranium dioxide UO$$_{2}$$ under high pressure

Sakai, Hironori; Kato, Harukazu; Tokunaga, Yo; Kambe, Shinsaku; Walstedt, R. E.; Nakamura, Akio; Tateiwa, Naoyuki*; Kobayashi, Tatsuo*

Journal of Magnetism and Magnetic Materials, 272-276(Suppl.), p.e413 - e414, 2004/05

https://doi.org/10.1016/j.jmmm.2003.11.307
 Times Cited Count：2 Percentile：13.76(Materials Science, Multidisciplinary)

The d.c. magnetization of insulating UO$$_{2}$$ under high pressure up to about 1 GPa has been measured using a piston-cylinder cell. Pressure-induced weak ferromagnetism was found to appear at low pressure (about 0.2 GPa). Both the remanent magnetization and the coercive force increase as pressure increases. This weak ferromagnetism may come from spin canting or from uncompensated moments around grain boundaries.

Journal Articles

NQR measurements of UTGa$$_{5}$$

Kato, Harukazu; Sakai, Hironori; Kambe, Shinsaku; Walstedt, R. E.; Tokiwa, Yoshifumi; Onuki, Yoshichika

Acta Physica Polonica B, 34(2), p.1063 - 1066, 2003/09

http://www.actaphys.uj.edu.pl/_cur/store/vol34/pdf/v34p1063.pdf

We performed $$^{69,71}$$Ga-NMR/NQR studies for UPtGa$$_{5}$$, which is a 5$$f$$-itinerant antiferromagnets with Neel temperature $$T_{N}$$ = 26 K and an electronic specific coefficient $$gamma$$ = 57 mJ/mol K$$^{2}$$. From the NMR spectrum in the paramagnetic temperature region, the hyperfine coupling constants $$A_{hf}^{para}$$ in the paramagnetic state have been evaluated. The magnitude of the transferred field has been evaluated from the zero-applied-field spectrum, yielding a value for the hyperfine coupling constant $$A_{hf}^{AF}$$ in the antiferromagnetic state. The estimated value of $$A_{hf}^{AF}$$ is an order of magnitude larger than that of $$A_{hf}^{para}$$. This implies the existence of a long-ranged hyperfine interaction path. The mechanism of the hyperfine interaction will be discussed in terms of RKKY interactions.

Journal Articles

Ga and Pt NMR study of UPtGa$$_{5}$$ and UNiGa$$_{5}$$

Kato, Harukazu; Sakai, Hironori; Tokunaga, Yo; Tokiwa, Yoshifumi; Ikeda, Shugo; Onuki, Yoshichika; Kambe, Shinsaku; Walstedt, R. E.

Journal of the Physical Society of Japan, 72(9), p.2357 - 2363, 2003/09

https://doi.org/10.1143/JPSJ.72.2357
 Times Cited Count：17 Percentile：66.96(Physics, Multidisciplinary)

Ga and Pt NMR measurements have been carried out for two isomorphs compounds, UPtGa$$_{5}$$ and UNiGa$$_{5}$$, which indicate different magnetic structures below T$$_{N}$$. Knight shift K measurements in the paramagnetic region are reported here. Transferred hyperfine coupling constants at Ga and Pt sites are determined. The temperature independent part K$$_{0}$$ of K, which probes the conduction electron polarization at the ligand site, has successfully evaluated. An nearly identical conduction electron structure in the paramagnetic region is suggested for the both compounds. The origin of the different magnetic structure is discussed.

Journal Articles

Pressure-induced weak ferromagnetism in uranium dioxide, UO$$_{2}$$

Sakai, Hironori; Kato, Harukazu; Tokunaga, Yo; Kambe, Shinsaku; Walstedt, R. E.; Nakamura, Akio; Tateiwa, Naoyuki*; Kobayashi, Tatsuo*

Journal of Physics; Condensed Matter, 15(28), p.S2035 - S2037, 2003/07

https://doi.org/10.1088/0953-8984/15/28/321
 Times Cited Count：3 Percentile：21.33(Physics, Condensed Matter)

The cubic-fluorite type uranium dioxide UO$$_2$$ is an ionically bounded insulator with localized magnetic moments of U$$^{4+}$$ (5$$f^{2}$$) ions. Under atmospheric pressure, UO$$_2$$ exhibits a first order antiferromagnetic transition at $$T_{rm N}$$=30.8 K accompanied by a small lattice distortion. In order to clarify the interrelation between QQ and exchange interactions in this system, we performed d.c. magnetization measurement under high pressure up to about 1 GPa by a piston-cylinder-type cramped cell. From the d.c. magnetization measurements under high pressure ($$ge$$ 0.1 GPa), it is found that UO$$_2$$ shows a weak-ferromagnetic-like transition at $$sim$$ 30 K, where the transition temperature is almost independent of external pressure up to 1 GPa. The ferromagnetic component per uranium atom is very small ($$sim 0.05 mu_{rm B}$$), although its component is dependent of pressure. This small ferromagnetic component may come from a canted antiferromagnetic ordering.

Journal Articles

Ga nuclear magnetic resonance study of UTGa$$_{5}$$(T=Ni, Pt)

Kato, Harukazu; Sakai, Hironori; Tokunaga, Yo; Tokiwa, Yoshifumi; Ikeda, Shugo; Onuki, Yoshichika; Kambe, Shinsaku; Walstedt, R. E.

Journal of Physics; Condensed Matter, 15(28), p.S2001 - S2005, 2003/07

https://doi.org/10.1088/0953-8984/15/28/314
 Times Cited Count：4 Percentile：26.93(Physics, Condensed Matter)

UPtGa$$_{5}$$ and UNiGa$$_{5}$$ are 5$$f$$-itinerant antiferromagnets with N$'{e}$el temperature $$T_{N}$$ = 26 K (Pt), 86 K (Ni). Remarkably, although the two compounds show almost identical Fermi surface properties in the paramagnetic state, recent neutron scattering experiments reveal that UPtGa$$_{5}$$ and UNiGa$$_{5}$$ are quite different in magnetic structure below $$T_{N}$$. In the microscopic viewpoint, we have carried out $$^{69,71}$$Ga NMR/NQR measurements for the both coumpounds. We have suceeded in separating the temperature independent term and the Curie-like-temperature-dependent term of the Knight shift $$K$$. This should be a good starting point in considering the magnetism of this system.

Journal Articles

Orbital ordering in UGa$$_{3}$$; Detection by 69Ga NMR

Kambe, Shinsaku; Kato, Harukazu; Sakai, Hironori; Walstedt, R. E.; Aoki, Dai*; Haga, Yoshinori; Onuki, Yoshichika

Physical Review B, 66(22), p.220403_1 - 220403_4, 2002/12

https://doi.org/10.1103/PhysRevB.66.220403
 Times Cited Count：9 Percentile：45.24(Materials Science, Multidisciplinary)

69Ga NMR has been measured in the paramagnetic and antiferromagnetic states of UGa$$_{3}$$(TN=67K). The temperature dependence of Knight shift has been determined. Based on the temperature dependence of static susceptibility, K- chi ploy is obtained. The slope of the plot corresponds to the hyperfine coupling constant. The hyperfine coupling constant is changed at TN and the second transition 40K. This fact indicates that the electronic sturcture is changed drastically at the transitions.

Journal Articles

Low-temperature structural change and magnetic anomaly in superconducting Cd$$_{2}$$Re$$_{2}$$O$$_{7}$$

Sakai, Hironori; Kato, Harukazu; Kambe, Shinsaku; Walstedt, R. E.; Ono, Hiroyuki*; Kato, Masaki*; Yoshimura, Kazuyoshi*; Matsuhata, Hirofumi*

Physical Review B, 66(10), p.100509_1 - 100509_4, 2002/09

https://doi.org/10.1103/PhysRevB.66.100509
 Times Cited Count：25 Percentile：72.83(Materials Science, Multidisciplinary)

The structural phase transition at $$T^{*}sim$$ 200 K in the superconducting pyrochlore oxide Cd$$_{2}$$Re$$_{2}$$O$$_{7}$$ has been investigated using X-ray and electron diffraction experiments and $$^{111}$$Cd NMR measurements. The susceptibility for Cd$$_{2}$$Re$$_{2}$$O$$_{7}$$ in the high temperature region ($$Tgg T^{*}$$) obeys a Curie-Weiss law with a large and negative Weiss temperature, which indicates that this system possesses a localized moment nature with antiferromagnetic interactions, leading to geometrical frustration. X-ray and electron diffraction measurements suggest the tetramerization of Re below $$T^{*}$$, which induces a nano-sized stripe structure. From $$^{111}$$Cd NMR experiments, a large orbital susceptibility is identified by means of a $$K$$-$$chi$$ plot. Both the spin susceptibility and $$(T_{1}T)^{-1}$$ are found to decrease sharply below $$T^{*}$$, signaling a decrease in density of states which is apparently caused by a developing partial energy gap at the Fermi surface.

Journal Articles

Ga and Pt NMR study of UPtGa$$_{5}$$

Kato, Harukazu; Sakai, Hironori; Tokiwa, Yoshifumi; Kambe, Shinsaku; Walstedt, R. E.; Onuki, Yoshichika

Journal of Physics and Chemistry of Solids, 63(6-8), p.1197 - 1200, 2002/06

https://doi.org/10.1016/S0022-3697(02)00010-0
 Times Cited Count：11 Percentile：50.72(Chemistry, Multidisciplinary)

no abstracts in English

Journal Articles

NMR study of the ordered state in UGa$$_{3}$$

Kambe, Shinsaku; Kato, Harukazu; Sakai, Hironori; Walstedt, R. E.; Haga, Yoshinori; Aoki, Dai*; Onuki, Yoshichika*

Physica B; Condensed Matter, 312-313, p.902 - 903, 2002/03

https://doi.org/10.1016/S0921-4526(01)01521-6
 Times Cited Count：6 Percentile：34.98(Physics, Condensed Matter)

We have measuered NMR in the paramagnetic and antiferromagnetic states of UGa$$_{3}$$ in order to discuss the spin structure in the antiferromagnetic state.

Oral presentation

Rh substitution effect of CeRu$$_{2}$$Al$$_{10}$$

Kobayashi, Riki; Kawamura, Yukihiro*; Hirai, Daishi*; Nishioka, Takashi*; Kato, Harukazu*; Matsumura, Masahiro*; Matsubayashi, Kazuyuki*; Uwatoko, Yoshiya*; Kaneko, Koji

no journal, , 

no abstracts in English

Oral presentation

Rh substitution effect of Ru-site for single crystals of CeRu$$_2$$Al$$_{10}$$

Kobayashi, Riki; Kawamura, Yukihiro*; Nishioka, Takashi*; Kato, Harukazu*; Matsumura, Masahiro*; Matsubayashi, Kazuyuki*; Uwatoko, Yoshiya*; Kaneko, Koji

no journal, , 

no abstracts in English

20 (Records 1-20 displayed on this page)
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