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Journal Articles

$$^{239}$$Pu nuclear magnetic resonance in the candidate topological insulator PuB$$_4$$

Dioguardi, A. P.*; Yasuoka, Hiroshi*; Thomas, S. M.*; Sakai, Hironori; Cary, S. K.*; Kozimor, S. A.*; Albrecht-Schmitt, T. E.*; Choi, H. C.*; Zhu, J.-X.*; Thompson, J. D.*; et al.

Physical Review B, 99(3), p.035104_1 - 035104_6, 2019/01

 Times Cited Count:2 Percentile:22.92(Materials Science, Multidisciplinary)

We present a detailed nuclear magnetic resonance (NMR) study of $$^{239}$$Pu in bulk and powdered single-crystal plutonium tetraboride (PuB$$_4$$), which has recently been investigated as a potential correlated topological insulator. The $$^{239}$$Pu NMR spectra are consistent with axial symmetry of the shift tensor showing for the first time that $$^{239}$$Pu NMR can be observed in an anisotropic environment and up to room temperature. The temperature dependence of the $$^{239}$$Pu shift, combined with a relatively long spin-lattice relaxation time ($$T_1$$), indicate that PuB$$_4$$ adopts a nonmagnetic state with gaplike behavior consistent with our density functional theory calculations. The temperature dependencies of the NMR Knight shift and $$T^{-1}$$ imply bulk gaplike behavior confirming that PuB$$_4$$ is a good candidate topological insulator.

Journal Articles

Emergent Weyl fermion excitations in TaP explored by $$^{181}$$Ta quadrupole resonance

Yasuoka, Hiroshi; Kubo, Tetsuro*; Kishimoto, Yasuki*; Kasinathan, D.*; Schmidt, M.*; Yan, B.*; Zhang, Y.*; To, Hideki*; Felser, C.*; Mackenzie, A. P.*; et al.

Physical Review Letters, 118(23), p.236403_1 - 236403_6, 2017/07

 Times Cited Count:23 Percentile:86.13(Physics, Multidisciplinary)

The $$^{181}$$Ta quadrupole resonance (NQR) technique has been utilized to investigate the microscopic magnetic properties of the Weyl semi-metal TaP. We found three zero-field NQR signals associated with the transition between the quadrupole split levels for Ta with $$I$$=7/2 nuclear spin. A quadrupole coupling constant, $$nu_Q$$ = 19.250 MHz, and an asymmetric parameter of the electric field gradient, $$eta$$= 0.423 were extracted, in good agreement with the theoretical calculations. In order to examine the magnetic excitations, the temperature dependence of the spin lattice relaxation rate (1/$$T_1T$$) has been measured for the $$f_2$$-line ($$pm 5/2 leftrightarrow pm 3/2$$ transition). We found that there exist two regimes with quite different relaxation processes. Above $$T$$*$$approx$$K, a pronounced ($$1/T_1T) propto T^2$$ behavior was found which is attributed to the magnetic excitations at the Weyl nodes with temperature dependent orbital hyperfine coupling. Below $$T$$*, the relaxation is mainly governed by Korringa process with (1/$$T_1T$$) = constant, while we have to include a $$T^{-1/2}$$ type dependence in order to reproduce our experimental data. We show that Ta-NQR is a novel probe for the bulk Weyl fermions and their excitations.

Journal Articles

Local moments in the heterogeneous electronic state of Cd-substituted CeCoIn$$_5$$; NQR relaxation rates

Sakai, Hironori; Ronning, F.*; Hattori, Takanori; Tokunaga, Yo; Kambe, Shinsaku; Zhu, J.-X.*; Wakeham, N.*; Yasuoka, Hiroshi; Bauer, E. D.*; Thompson, J. D.*

Journal of Physics; Conference Series, 807(3), p.032001_1 - 032001_6, 2017/04

 Times Cited Count:1 Percentile:41.97

We have used nuclear quadrupole resonance (NQR) to probe microscopically the response of a prototypical quantum critical metal CeCoIn$$_5$$ to substitutions of small amounts of Cd for In. Approximately half of the Cd substituents induce local Ce moments in their close proximity, as observed by site-dependent longitudinal nuclear spin relaxation rates $$1/T_1$$. To reaffirm that localized $$f$$ moments are induced around the Cd substituents, we find a Gaussian spin-echo decay rate $$1/T_{rm 2G}$$ of transverse nuclear spin relaxation. Further, $$T_1T/T_{rm 2G}^2$$ for the NQR subpeak is found to be proportional to temperatures, again indicating local moments fluctuations around the Cd substituents, while that for the NQR main peak shows a $$T^{0.7}$$-dependence. The latter temperature dependence is close to 0.75 in pure CeCoIn$$_5$$ and indicates that the bulk electronic state is located close to a two dimensional quantum critical instability.

Journal Articles

Chiral magnetism in an itinerant helical magnet, MnSi; An Extended $$^{29}$$Si NMR study

Yasuoka, Hiroshi; Motoya, Kiyoichiro*; Majumder, M.*; Witt, S.*; Kerllner, C.*; Baenitz, M.*

Journal of the Physical Society of Japan, 85(7), p.073701_1 - 073701_4, 2016/07

 Times Cited Count:3 Percentile:33.69(Physics, Multidisciplinary)

Journal Articles

Microscopic investigation of electronic inhomogeneity induced by substitutions in a quantum critical metal CeCoIn$$_5$$

Sakai, Hironori; Ronning, F.*; Zhu, J.-X.*; Wakeham, N.*; Yasuoka, Hiroshi; Tokunaga, Yo; Kambe, Shinsaku; Bauer, E. D.*; Thompson, J. D.*

Physical Review B, 92(12), p.121105_1 - 121105_5, 2015/09

 Times Cited Count:14 Percentile:59.87(Materials Science, Multidisciplinary)

Chemical substitutions are used commonly to tune a magnetic transition to zero temperature, but the resulting non-Fermi liquid (NFL) behavior is non-universal. We have used nuclear quadrupole resonance (NQR) to probe microscopically the response of a prototypical quantum-critical metal CeCoIn$$_5$$ to substitutions of small amounts of Sn and Cd for In. These substituents induce very different local electronic environments as observed by site dependent spin lattice relaxation rates $$1/T_1$$ that influence the NFL behavior. The effects found here illustrate the need for care in interpreting NFL properties determined by macroscopic measurements.

Journal Articles

Observation of Barnett fields in solids by nuclear magnetic resonance

Chudo, Hiroyuki; Ono, Masao; Harii, Kazuya; Matsuo, Mamoru; Ieda, Junichi; Haruki, Rie*; Okayasu, Satoru; Maekawa, Sadamichi; Yasuoka, Hiroshi; Saito, Eiji

Applied Physics Express, 7(6), p.063004_1 - 063004_4, 2014/06

 Times Cited Count:35 Percentile:84.13(Physics, Applied)

A magnetic field is predicted to emerge on a particle in a rotating body even if the body is electrically neutral. This emergent field is called a Barnett field. We show that nuclear magnetic resonance (NMR) enables direct measurement of the Barnett field in solids. We rotated both a sample and an NMR coil synchronously at high speed and found an NMR shift whose sing reflects that of the nuclear magnetic moments. This result provides direct evidence of the Barnett field. The use of NMR for Barnett field measurement enables the unknown signs of nuclear magnetic moments in solids to be determined.

Journal Articles

Microscopic properties of the heavy-fermion superconductor PuCoIn$$_5$$ explored by nuclear quadrupole resonance

Koutroulakis, G.*; Yasuoka, Hiroshi; Chudo, Hiroyuki; Tobash, P. H.*; Mitchell, J. N.*; Bauer, E. D.*; Thompson, J. D.*

New Journal of Physics (Internet), 16, p.053019_1 - 053019_12, 2014/05

 Times Cited Count:6 Percentile:49.45(Physics, Multidisciplinary)

We report $$^{115}$$In nuclear quadrupolar resonance (NQR) measurements on the heavy-fermion superconductor PuCoIn$$_5$$, in the temperature range 0.29 K $$leq Tleq$$75 K. The NQR parameters for the two crystallographically inequivalent In sites are determined, and their temperature dependence is investigated. A linear shift of the quadrupolar frequency with lowering temperature below the critical value $$T_c$$ is revealed, in agreement with the prediction for composite pairing. The nuclear spin-lattice relaxation rate $$T_1^{-1}(T)$$ clearly signals a superconducting (SC) phase transition at $$T_c simeq $$ 2.3 K, with strong spin fluctuations, mostly in-plane, dominating the relaxation process in the normal state near to $$T_c$$. Analysis of the $$T_1^{-1}$$ data in the SC state suggests that PuCoIn$$_5$$ is a strong-coupling $$d$$-wave superconductor.

Journal Articles

Weak itinerant antiferromagnetism in PuIn$$_3$$ explored using $$^{115}$$In nuclear quadrupole resonance

Chudo, Hiroyuki; Koutroulakis, G.*; Yasuoka, Hiroshi; Bauer, E. D.*; Tobash, P. H.*; Mitchell, J. N.*; Thompson, J. D.*

Journal of Physics; Condensed Matter, 26(3), p.036001_1 - 036001_5, 2014/01

 Times Cited Count:5 Percentile:27.7(Physics, Condensed Matter)

The results of $$^{115}$$In nuclear quadrupole resonance (NQR) measurements on PuIn$$_3$$ are reported. Three of the four NQR lines of $$^{115}$$In expected for nuclear spin $$I$$=9/2 are observed. The equal spacing of these lines at 20 K yields the NQR frequency of $$nu_{rm Q}$$=10.45 MHz, and the asymmetry parameter of the electric field gradient, $$eta$$=0. The NQR line profile and the nuclear spin-lattice relaxation rate $$1/T_1$$ display an abrupt change at 14 K, which is associated with the onset of long-range antiferromagnetic order. The temperature dependences of the staggered magnetization $$M_{rm Q}(T)$$, extracted from the NQR spectra, and $$1/T_1$$ below $$T_{rm N}$$=14 K are well explained by the self-consistent renormalization (SCR) theory for spin fluctuations. In addition, scaling between $$T_1T$$ and $$M_{rm Q}(T)/M_{rm Q}(0)$$ is also consistent with the predictions of SCR theory, providing further evidence that PuIn$$_3$$ is a weak itinerant antiferromagnet in which spin fluctuations around the antiferromagnetic wave vector play a major role in the system's behavior at finite temperatures.

Journal Articles

Observation of $$^{239}$$Pu nuclear magnetic resonance

Yasuoka, Hiroshi; Koutroulakis, G.*; Chudo, Hiroyuki; Richmond, S.*; Veirs, D. K.*; Smith, A. I.*; Bauer, E. D.*; Thompson, J. D.*; Jarvinen, G. D.*; Clark, D. L.*

Science, 336(6083), p.901 - 904, 2012/05

 Times Cited Count:42 Percentile:86.45(Multidisciplinary Sciences)

Journal Articles

CeRu$$_2$$Al$$_2$$B; A Local-moment 4$$f$$ magnet with a complex $$T$$-$$H$$ phase diagram

Raumbach, R. E.*; Chudo, Hiroyuki; Yasuoka, Hiroshi; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Physical Review B, 85(9), p.094422_1 - 094422_7, 2012/03

 Times Cited Count:27 Percentile:75.89(Materials Science, Multidisciplinary)

Journal Articles

$$^{237}$$Np nuclear relaxation rate in heavy fermion superconductor NpPd$$_5$$ Al$$_2$$

Chudo, Hiroyuki; Tokunaga, Yo; Kambe, Shinsaku; Sakai, Hironori; Haga, Yoshinori; Matsuda, Tatsuma; Onuki, Yoshichika; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; et al.

Physical Review B, 84(9), p.094402_1 - 094402_5, 2011/09

 Times Cited Count:6 Percentile:31.79(Materials Science, Multidisciplinary)

Journal Articles

Spin pumping efficiency from half metallic Co$$_2$$MnSi

Chudo, Hiroyuki; Ando, Kazuya*; Saito, Kesami*; Okayasu, Satoru; Haruki, Rie; Sakuraba, Yuya*; Yasuoka, Hiroshi; Takanashi, Koki; Saito, Eiji

Journal of Applied Physics, 109(7), p.073915_1 - 073915_4, 2011/04

 Times Cited Count:16 Percentile:59.6(Physics, Applied)

We present spin pumping using a Heusler alloy Co$$_2$$MnSi/Pt bilayer film. A spin current is produced by a ferromagnetic resonance (FMR) technique. The pure spin current injected into the Pt layer from the Co$$_2$$MnSi layer is detected by the inverse spin-Hall effect (ISHE), which converts the spin current into an electric current. We estimated a damping constant of the Co$$_2$$MnSi/Pt bilayer film from an angular dependence of FMR spectra. Using the damping constant efficiency of spin pumping from the Co$$_2$$MnSi layer is evaluated. We found that a mixing conductance at the Co$$_2$$MnSi/Pt interface is comparable to that at a permalloy/Pt interface.

Journal Articles

Low temperature structure of FeSr$$_{2}$$YCu$$_{2}$$O$$_{6+delta}$$ magnetic superconductor

Mochiku, Takashi*; Hata, Yoshiaki*; Wuernisha, T.*; Igawa, Naoki; Hoshikawa, Akinori*; Ishigaki, Toru*; Yasuoka, Hiroshi*; Hirata, Kazuto*

Physica C, 470(Suppl.1), p.S158 - S159, 2010/12

 Times Cited Count:2 Percentile:13.13(Physics, Applied)

We have performed neutron powder diffraction of the superconducting FeSr$$_{2}$$YCu$$_{2}$$O$$_{6+}$$$$_{delta}$$ and the nonsuperconducting FeSr$$_{2}$$Y(Cu$$_{0.95}$$Zn$$_{0.05}$$)$$_{2}$$O$$_{6+}$$$$_{delta}$$ samples at low temperature and room temperature to investigate the relation between the crystal structure ant the physical properties. Neutron diffraction study indicates that the magnetic order in this compound is not long-range order because we observed no extra reflection due to the magnetic superstructure. We have observed structural anomaly related to Cu in the superconducting sample around 30 K although we could not observe it in the nonsuperconducting sample. There is possibility of the change of the charge distribution around 30 K in the superconducting sample.

Journal Articles

La substitution effect and hyperfine-enhanced $$^{141}$$Pr nuclear spin dynamics in PrPb$$_3$$; $$^{139}$$La NMR study in Pr$$_{0.97}$$La$$_{0.03}$$Pb$$_3$$

Tokunaga, Yo; Sakai, Hironori; Chudo, Hiroyuki; Kambe, Shinsaku; Yasuoka, Hiroshi; Suzuki, Hiroyuki*; Walstedt, R. E.*; Homma, Yoshiya*; Aoki, Dai*; Shiokawa, Yoshinobu*

Physical Review B, 82(10), p.104401_1 - 104401_6, 2010/09

 Times Cited Count:5 Percentile:28.15(Materials Science, Multidisciplinary)

$$^{139}$$La NMR studies have been performed on PrPb$$_3$$ substituted with 3% La. The temperature dependence of the local magnetic susceptibility around La ions has been extracted from the $$^{139}$$La Knight shift. These data show that the non-magnetic $$Gamma_3$$ crystalline-electric-field (CEF) ground state (GS) is preserved even at the nearest neighboring Pr ions, although their CEF level scheme is slightly modified due to the La substitution. On the other hand, the temperature dependence of the nuclear spin-lattice relaxation rate $$1/T_1$$ is found to be well reproduced by assuming the same CEF level scheme over a wide temperature range. However, $$1/T_1$$ shows a strong upturn below 10 K, which is not expected from the non-magnetic CEF GS. We show that the low temperature anomaly can be quantitatively understood in terms of a cross-relaxation process between $$^{141}$$Pr and $$^{139}$$La nuclear spins.

Journal Articles

Anisotropic spin fluctuations in heavy-fermion superconductor NpPd$$_5$$Al$$_2$$

Chudo, Hiroyuki; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Aoki, Dai*; Homma, Yoshiya*; Haga, Yoshinori; Matsuda, Tatsuma; Onuki, Yoshichika; Yasuoka, Hiroshi

Journal of the Physical Society of Japan, 79(5), p.053704_1 - 053704_4, 2010/05

 Times Cited Count:12 Percentile:62.18(Physics, Multidisciplinary)

We present $$^{27}$$Al NMR measurements of the Knight shift and nuclear spin-lattice relaxation rate 1/$$T$$$$_1$$ in the normal state for a single crystal of the heavy-fermion superconductor NpPd$$_5$$ Al$$_2$$ ($$T$$$$_{rm c}$$ = 4.9 K). We report here that 1/$$T$$$$_1$$ shows a large anisotropy with a different temperature dependence for $$H$$ $$parallel$$ $$a$$ and $$H$$ $$parallel$$ $$c.$$ 1/$$T$$$$_1$$ for $$H$$ $$parallel$$ $$c$$ shows a power-law temperature dependence $$sim$$$$T$$$$^{0.38}$$, while 1/$$T$$$$_1$$ for $$H$$ $$parallel$$ $$a$$ shows a $$T$$-linear dependence at low temperatures in fields well above $$H$$$$_{rm c2}$$. From the analysis of 1/$$T$$$$_1$$, $$XY$$-type anisotropy of AFM spin fluctuations is found to become prominent below 20 K.

Journal Articles

Quantum criticality in a uranium heavy fermion system revealed with NMR spin-spin relaxation

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Matsuda, Tatsuma; Haga, Yoshinori; Yasuoka, Hiroshi; Chudo, Hiroyuki; Walstedt, R. E.*

Journal of Physics; Conference Series, 200, p.012076_1 - 012076_4, 2010/02

 Times Cited Count:1 Percentile:49.66

In order to clarify quantum criticality in heavy fermion systems, we propose to use the Gaussian spin-echo decay rate $$1/T_{2G}$$ of the NMR spin-spin relaxation. In contrast to the spin-lattice relaxation rate $$1/T_1$$, which is connected with the dynamical susceptibility Im$$chi(q,omega)$$, $$1/T_{2G}$$ is driven by the static susceptibility Re$$chi(q,0)$$ at finite $$q$$ for an antiferromagnet. The combined quantity $$T_1T/T_{2G}^2$$ is found to provide key information in determining the nature of quantum criticality. The $$T$$-dependence of $$T_1T/T_{2G}^2$$ for the Sn site in the heavy fermion compound USn$$_3$$ is presented as an example.

Journal Articles

$$^{105}$$Pd NQR study on NpPd$$_5$$Al$$_2$$ and CePd$$_5$$Al$$_2$$

Chudo, Hiroyuki; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Aoki, Dai*; Haga, Yoshinori; Matsuda, Tatsuma; Homma, Yoshiya*; Nakano, Yasunori*; Honda, Fuminori*; et al.

Journal of Physics; Conference Series, 200, p.012020_1 - 012020_4, 2010/02

 Times Cited Count:3 Percentile:77.33

We report the results of $$^{105}$$Pd NQR experiments on NpPd$$_5$$Al$$_2$$ and CePd$$_5$$Al$$_2$$. In the normal state at 6 K, the $$^{105}$$Pd NQR spectrum consists of four lines in both systems. These lines can be assigned to two sets of $$pm1/2leftrightarrowpm3/2$$ and $$pm3/2leftrightarrowpm5/2$$ NQR transitions arising from two crystallographically in equivalent Pd sites. From the analysis of the $$^{105}$$Pd NQR spectrum the nuclear quadrupole frequency $$nu_Q$$, asymmetry parameter $$eta$$ and electric field gradient $$V_{zz}$$ have been deduced.

Journal Articles

Hyperfine interactions in the itinerant system UFeGa$$_{5}$$

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Chudo, Hiroyuki; Yasuoka, Hiroshi; Matsuda, Tatsuma; Haga, Yoshinori; Ikeda, Shugo; Nakamura, Akio; Yamamoto, Etsuji; et al.

Journal of Nuclear Materials, 385(1), p.1 - 3, 2009/03

 Times Cited Count:1 Percentile:10.95(Materials Science, Multidisciplinary)

In 5f-electron systems, exotic magnetism and unconventional superconductivity appear at low temperatures owing to strong electron correlations and orbital degeneracy. For example, we have investigated the unconventional superconducting states of recently synthesized NpPd$$_5$$Al$$_2$$ ($$T_c$$=5K) and PuRhGa$$_5$$ ($$T_c$$=9K) in terms of both macroscopic (staticsusceptibility, specific heat, resistivity) and microscopic (NMR) probes. The relation between magnetic fluctuations and unconventional superconductivity in f-electron systems is also discussed. Another exciting topic concerns the series AnO$$_2$$ (An; U, Np, Pu, Am). Besides the importance of AnO$$_2$$ as a nuclear fuel, the magnetic properties of these compounds at low temperatures are particularly interesting. On the basis of $$^{17}$$O-NMR studies, multipolar ordered states have been identified in UO$$_2$$ (dipolar + quadrupolar ordering) and NpO$$_2$$ (quadrupolar + octupolar ordering), in contrast with the non-magnetic ground state of PuO$$_2$$.

Journal Articles

Localized 5$$f$$ antiferromagnetism in cubic UIn$$_3$$; $$^{115}$$In-NMR/NQR study

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Chudo, Hiroyuki; Tokiwa, Yoshifumi*; Aoki, Dai*; Haga, Yoshinori; Onuki, Yoshichika; Yasuoka, Hiroshi

Physical Review B, 79(10), p.104426_1 - 104426_7, 2009/03

 Times Cited Count:6 Percentile:31.42(Materials Science, Multidisciplinary)

$$^{115}$$In nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been performed on an antiferromagnet UIn$$_3$$ with the cubic AuCu$$_3$$-type structure. Under zero field, the observation of the NQR spectrum has led to an estimated $$nu_{rm Q}$$ of 11.8 MHz at 90 K. The temperature variation of the NQR relaxation rates ($$1/T_1$$) far above the N${'e}$el temperature $$T_{rm N}$$=88 K approaches a constant value, which indicates a localized nature for the $$5f$$-electrons in this system. On the other hand, in the antiferromagnetically ordered state, we propose that the most plausible direction of antiferromagnetic U moments may be $$langle 110rangle$$ among the possible orientations of $$langle 100rangle$$, $$langle 110rangle$$, or $$langle 111rangle$$.

Journal Articles

$$^{31}$$P-NMR study of hyperfine interactions and magnetic fluctuations in the neptunium-based filled skutterudite NpFe$$_{4}$$P$$_{12}$$

Tokunaga, Yo; Kambe, Shinsaku; Sakai, Hironori; Chudo, Hiroyuki; Matsuda, Tatsuma; Haga, Yoshinori; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; et al.

Physical Review B, 79(5), p.054420_1 - 054420_7, 2009/02

 Times Cited Count:5 Percentile:27.24(Materials Science, Multidisciplinary)

$$^{31}$$P-NMR measurements have been performed on a single crystal of the neptunium-based filled skutterudite NpFe$$_{4}$$P$$_{12}$$. We have observed transferred hyperfine interactions at the P sites, which lead to an estimate of the local spin density in the P 3$$p$$ orbitals. It is shown that a fraction of the Np 5$$f$$ spin moments is transferred mostly into the P 3$$p$$ orbitals extending toward the inside of a P-cage. The weak hybridization between Np 5$$f$$ and P 3$$p$$ orbitals suggests a localized character for Np 5$$f$$ electrons. We have also measured the field and temperature dependences of the nuclear spin-lattice relaxation rate ($$1/T_1$$). The $$1/T_1$$ data reveal that the low-energy spin fluctuations of Np 5$$f$$ spin moments are strongly suppressed by applied fields over a relatively wide temperature range. The present NMR results demonstrate that the negative magnetoresistance comes from a reduction of the magnetic scattering from Np 5$$f$$ spin moments by an applied field.

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