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Journal Articles

Universal scaling behavior under pressure in the heavy-fermion antiferromagnet CeRh$$_2$$Si$$_2$$; $$^{29}$$Si NMR study

Sakai, Hironori; Matsumoto, Yuji*; Haga, Yoshinori; Tokunaga, Yo; Kambe, Shinsaku

Physical Review B, 103(8), p.085114_1 - 085114_8, 2021/02

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

The microscopic origin of a magnetic phase diagram under pressure in a heavy fermion antiferromagnet CeRh$$_2$$Si$$_2$$ was investigated using the $$^{29}$$Si nuclear magnetic resonance (NMR) technique. We investigated the temperature and pressure dependencies of $$q$$-independent local fluctuations caused by the single-site Kondo effect. A universal scaling behavior observed on the energy scale of the local fluctuations in an entire pressure region demonstrates that a characteristic energy scale $$T_0$$ of Kondo interactions monotonically increases by applying pressure without a critical anomaly around the quantum critical pressure $$P_{rm c}$$ of antiferromagnetism. Our NMR result agrees with the Doniach picture of the heavy-fermion phase diagram, where the progressive delocalization of the $$f$$-electrons occurs across $$P_{rm c}$$, accompanied by the development of antiferromagnetic correlations among the $$f$$-electrons.

Journal Articles

Novel universality class for the ferromagnetic transition in the low carrier concentration systems UTeS and USeS exhibiting large negative magnetoresistance

Tateiwa, Naoyuki; Haga, Yoshinori; Sakai, Hironori; Yamamoto, Etsuji

Physical Review B, 100(6), p.064413_1 - 064413_7, 2019/08

 Times Cited Count:1 Percentile:10.83(Materials Science, Multidisciplinary)

We report the novel critical behavior of magnetization in low carrier concentration systems UTeS and USeS that exhibit the large negative magnetoresistance around the ferromagnetic transition temperatures $$T_{rm C}$$ $$sim$$ 85 and 23 K, respectively. We determine the critical exponents, $$beta$$ for the spontaneous magnetization $$M_{rm s}$$, $$gamma$$ for the magnetic susceptibility $$chi$$, and $$delta$$ for the magnetization isotherm at $$T_{rm C}$$ with several analytical methods. The ferromagnetic states in UTeS and USeS have strong uniaxial magnetic anisotropy. However, the critical exponents in the two compounds are different from those in the three-dimensional Ising system. Similar exponents have been reported for the uranium ferromagnetic superconductors UGe$$_2$$ and URhGe. An important finding is that the novel critical phenomenon appears regardless of the charge carrier density or the degree of the itinerancy of the $$5f$$ electrons.

Journal Articles

$$^{125}$$Te-NMR study on a single crystal of heavy fermion superconductor UTe$$_2$$

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Hattori, Taisuke; Higa, Nonoka; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 88(7), p.073701_1 - 073701_4, 2019/07

 Times Cited Count:29 Percentile:95.25(Physics, Multidisciplinary)

We report $$^{125}$$Te-NMR studies on a newly discovered heavy fermion superconductor UTe$$_2$$. Using a single crystal, we have measured the $$^{125}$$Te-NMR Knight shift $$K$$ and spin-lattice relaxation rate $$1/T_1$$ for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static ($$K$$) and dynamical susceptibilities ($$1/T_1$$) in the paramagnetic state above about 20 K. Around 20 K, however, we have observed a sudden loss of NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation rate $$1/T_2$$, when the field is applied along the easy axis of magnetization (=$$a$$ axis). This behavior suggests the development of longitudinal magnetic fluctuations along the $$a$$ axis at very low frequencies below 20 K.

Journal Articles

High-field phase diagram of the heavy-fermion metal CeIn$$_3$$; Pulsed-field NMR study on single crystals up to 56 T

Tokunaga, Yo; Orlova, A.*; Bruyant, N.*; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Higa, Nonoka; et al.

Physical Review B, 99(8), p.085142_1 - 085142_5, 2019/02

 Times Cited Count:3 Percentile:33.95(Materials Science, Multidisciplinary)

The heavy-fermion antiferromagnet CeIn$$_3$$ exhibits a field-induced anomaly associated with Fermi surface reconstruction at $$H^*sim$$ 45 T, well below the antiferromagnetic (AFM) critical field that exceeds 60 T. In order to explore the origin of this anomaly, we have measured $$^{115}$$In NMR spectra in pulsed magnetic fields up to 56 T using high-quality single crystals. To within experimental resolution, we do not detect any change in the NMR spectra that could suggest a modification in either the character of the hyperfine field or the electric field gradient at In sites through $$H^*$$. This strongly suggests that the 45 T anomaly cannot be simply ascribed to a field-induced change in the magnetic structure of the AFM state.

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

Phenomenological approach to study the degree of the itinerancy of the 5$$f$$ electrons in actinide ferromagnets with spin fluctuation theory

Tateiwa, Naoyuki; Posp$'i$$v{s}$il, J.*; Haga, Yoshinori; Sakai, Hironori; Matsuda, Tatsuma*; Yamamoto, Etsuji

Progress in Nuclear Science and Technology (Internet), 5, p.104 - 107, 2018/11

Uranium ferromagnetic superconductors UGe$$_2$$, URhGe and UCoGe have attracted much attention from both theoretical and experimental sides since the same 5$$f$$ electrons underlie carry both the ferromagnetism and superconductivity. Recently, we have analysed 69 uranium, 7 neptunium, and 4 plutonium ferromagnets with spin fluctuation theory originally developed for researches on itinerant ferromagnets in the 3$$d$$ transition metals and their intermetallics. The applicability of the spin fluctuation theory to the actinide 5$$f$$ system has been confirmed and the itinerant character of the 5f electrons is suggested in the actinide ferromagnets. In this conference, two results will be shown. One is the results of the analyses on 80 actinide ferromagnets and the other is the pressure dependence of the spin fluctuation parameters in UGe$$_2$$.

Journal Articles

Occupation sites and valence states of Co dopants in (La, Co)-codoped M-type Sr ferrite; $$^{57}$$Fe and $$^{59}$$Co nuclear magnetic resonance studies

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ueda, Hiroaki*; Tanioku, Yasuaki*; Michioka, Chishiro*; Yoshimura, Kazuyoshi*; Takao, Kenta*; Shimoda, Aiko*; et al.

Physical Review B, 98(6), p.064403_1 - 064403_10, 2018/08

 Times Cited Count:6 Percentile:45.58(Materials Science, Multidisciplinary)

To specify preferential occupation sites of Co substituents and to clarify charge and spin states of Co ions in (La, Co)-cosubstituted hexagonal magnetoplumbite-type (M-type) Sr ferrite, $$^{57}$$Fe and $$^{59}$$Co nuclear magnetic resonance (NMR) spectra are measured under zero and external magnetic fields using powdered and single crystalline specimens. To a considerable degree, the charge compensation between La$$^{3+}$$ and Co$$^{2+}$$ works in the equal (La, Co)-codoped case, where more than half of the Co ions are considered to be present in the minority spin $$4f_1$$ sites at the center of the oxygen tetrahedra, with the $$S$$ = 3/2 state carrying a small orbital moment owing to spin-orbit interaction. The remaining small number of high-spin Co$$^{2+}$$ ($$S$$ = 3/2, $$L$$ = 1) ions with unquenched orbital moments would be distributed to the other octahedral $$12k$$, $$2a$$, and $$4f_2$$ sites.

Journal Articles

Easy-plane XY spin fluctuations in the cycloidal magnet UPtGe studied via field orientation-dependent $$^{195}$$Pt NMR

Tokunaga, Yo; Nakamura, Ai*; Aoki, Dai*; Shimizu, Yusei*; Homma, Yoshiya*; Honda, Fuminori*; Sakai, Hironori; Hattori, Taisuke; Kambe, Shinsaku

Physical Review B, 98(1), p.014425_1 - 014425_5, 2018/07

 Times Cited Count:1 Percentile:8.26(Materials Science, Multidisciplinary)

$$^{195}$$Pt NMR measurements have been performed on a single crystal of the uranium-based compound UPtGe, which is the only 5f system known to possess an incommensurate helical (cycloidal) structure below TN = 50 K. Knight shift measurement confirmed the isotropic character of the static spin susceptibilities in hexagonal-like ac crystal planes of the EuAuGe-type crystal structure. The hyperfine coupling constants were also found to be isotropic in the planes. Nuclear relaxation rate measurement revealed the development of the antiferro-magnetic spin fluctuations with XY character confined to the hexagonal-like plane below 200 K. The results present a clear contrast to the Ising anisotropy of the fluctuations in ferromagnetic superconductors UCoGe and URhGe.

Journal Articles

Odd-parity electronic multipolar ordering in URu$$_2$$Si$$_2$$; Conclusions from Si and Ru NMR measurements

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Hattori, Taisuke; Higa, Nonoka; Matsuda, Tatsuma*; Haga, Yoshinori; Walstedt, R. E.*; Harima, Hisatomo*

Physical Review B, 97(23), p.235142_1 - 235142_10, 2018/06


 Times Cited Count:16 Percentile:77.41(Materials Science, Multidisciplinary)

Journal Articles

Ruderman-Kittel interaction between Si in URu$$_{2}$$Si$$_{2}$$

Kambe, Shinsaku; Hattori, Taisuke; Tokunaga, Yo; Sakai, Hironori; Matsuda, Tatsuma*; Haga, Yoshinori; Walstedt, R. E.*

Journal of Physics; Conference Series, 969(1), p.012033_1 - 012033_6, 2018/03

 Times Cited Count:1 Percentile:64.34

High quality URu$$_{2}$$Si$$_{2}$$ enriched in $$^{29}$$Si isotope, which is an NMR nucleus, by 52% was prepared. Since the natural abundance ratio of $$^{29}$$Si isotope is about 4%, the accumulated measurement time can be shortened to about one hundredth by this concentration. Results of the Si-NMR linewidth of hidden ordered phase using this single crystal sample have already been reported. In this report, we will report more detailed analysis on the magnetic field, temperature and angle of this line width We also discuss the possibility of distribution of magnetic susceptibility in two-fold symmetry by RKKY model.

Journal Articles

Evidence for spin singlet pairing with strong uniaxial anisotropy in URu$$_2$$Si$$_2$$ using nuclear magnetic resonance

Hattori, Taisuke; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Matsuda, Tatsuma*; Haga, Yoshinori

Physical Review Letters, 120(2), p.027001_1 - 027001_5, 2018/01

 Times Cited Count:10 Percentile:72.43(Physics, Multidisciplinary)

Journal Articles

Anisotropy of spin fluctuations in a tetragonal heavy fermion antiferromagnet CeRhAl$$_4$$Si$$_2$$

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ghimire, N. J.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Journal of Physics; Conference Series, 868(1), p.012012_1 - 012012_5, 2017/07

 Times Cited Count:1 Percentile:57.57

$$^{27}$$Al NMR experiments have been performed using a single crystal of CeRhAl$$_4$$Si$$_2$$. In the paramagnetic state, Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which has a local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. The relaxation rates suggest that 4$$f$$ electrons behave as local moments in the high temperatures. From the NMR spectral analyses, the antiferromagnetic structures are discussed.

Journal Articles

Nature of distributed two-fold ordering in URu$$_2$$Si$$_2$$

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Hattori, Taisuke; Walstedt, R. E.*

Journal of Physics; Conference Series, 868(1), p.012003_1 - 012003_7, 2017/07


 Times Cited Count:0 Percentile:0.04

In the hidden-ordered state of URu$$_2$$Si$$_2$$, a modest breaking of the fourfold symmetry was suggested in previous $$^{29}$$Si NMR basal-plane field rotation measurements. Based on the detail analysis of $$^{29}$$Si NMR linewidth, the occurrence of a distribution of twofold local fields at the Si sites is suggested even in a high-quality single crystal. A possible picture for the distributed two-fold ordering will be discussed.

Journal Articles

Itinerant ferromagnetism in actinide $$5f$$-electron systems; Phenomenological analysis with spin fluctuation theory

Tateiwa, Naoyuki; Posp$'i$$v{s}$il, J.*; Haga, Yoshinori; Sakai, Hironori; Matsuda, Tatsuma*; Yamamoto, Etsuji

Physical Review B, 96(3), p.035125_1 - 035125_15, 2017/07

 Times Cited Count:16 Percentile:72.62(Materials Science, Multidisciplinary)

We have carried out an analysis of magnetic data in 69 uranium, 7 neptunium and 4 plutonium ferromagnets with the spin fluctuation theory developed by Takahashi (Y. Takahashi, J. Phys. Soc. Jpn. ${bf 55}$, 3553 (1986)). The basic and spin fluctuation parameters of the actinide ferromagnets are determined and the applicability of the spin fluctuation theory to actinide $$5f$$ system has been discussed. Itinerant ferromagnets of the $$3d$$ transition metals and their intermetallics follow a generalized Rhodes-Wohlfarth relation $${p_{rm eff}}/{p_{rm s}}{,}{propto}{,}({T_{rm C}}/{T_0})^{-3/2}$$. Here, $$p_{rm s}$$, $$p_{rm eff}$$, $$T_{rm C}$$, and $$T_0$$ are the spontaneous and effective magnetic moments, the Curie temperature and the width of spin fluctuation spectrum in energy space, respectively. The same relation is satisfied for $${T_{rm C}}/{T_0}< 1.0$$ in the most of the actinide ferromagnets.

Journal Articles

$$T$$ dependence of nuclear spin-echo decay at low temperatures in YbRh$$_2$$Si$$_2$$

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Hattori, Taisuke; Lapertot, G.*; Matsuda, Tatsuma*; Knebel, G.*; Flouquet, J.*; Walstedt, R. E.*

Physical Review B, 95(19), p.195121_1 - 195121_8, 2017/05


 Times Cited Count:3 Percentile:23.04(Materials Science, Multidisciplinary)

The authors report $$^{29}$$Si nuclear spin-echo oscillations and decay measurements on a single crystal of YbRh$$_2$$Si$$_2$$. These quantities are found to be $$T$$ independent from 300 K down to $$sim$$20 K, showing, however, a strong $$T$$ dependence below 20 K. These results indicate that electronic states near the Fermi level are modified at low temperatures. The observed spin-echo oscillations can be interpreted with the Ruderman-Kittel and pseudo-dipolar interactions between nearest-neighbor Si nuclei driven by conduction electron scattering at the Fermi surface. Possible modifications to the Fermi surface at low temperatures are discussed.

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

No detectable change in in-plane $$^{29}$$Si knight shift in the superconducting state of URu$$_2$$Si$$_2$$

Hattori, Taisuke; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Matsuda, Tatsuma*; Haga, Yoshinori

Journal of the Physical Society of Japan, 85(7), p.073711_1 - 073711_4, 2016/07

 Times Cited Count:7 Percentile:56.08(Physics, Multidisciplinary)

Using a high-quality single crystal of URu$$_2$$Si$$_2$$, we performed $$^{29}$$Si Knight shift measurements with an applied magnetic field $$H^a$$ along the crystalline $$a$$ axis, i.e., along the magnetic hard axis, for temperatures down to 50 mK. The narrow, single-peak $$^{29}$$Si NMR spectrum obtained from this crystal allowed us to examine the temperature variation of the Knight shift $$K(T)$$, and hence, that of the variation of the spin susceptibility with sensitivity on the order of 0.001%. At this precision, no observable change in $$K(T)$$ was detected from 50 mK up to the superconducting transition at $$T_{rm SC}(H^a)sim$$ 1 K. Our results correspond to either an extremely small spin susceptibility in the hidden-order state along the magnetic hard axis or to possible spin-triplet superconductivity in this system.

Journal Articles

Interplay between quantum fluctuations and reentrant superconductivity with a highly enhanced upper critical field in URhGe

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Hattori, Taisuke; Kambe, Shinsaku; et al.

Physical Review B, 93(20), p.201112_1 - 201112_5, 2016/05

 Times Cited Count:12 Percentile:59.65(Materials Science, Multidisciplinary)

The ferromagnetic superconductor URhGe has been known to exhibit an extremely large enhancement of the upper critical field when the field is confined and rotated in the ($$ab$$) crystal plane. Our high-field $$^{59}$$Co NMR measurements on 10% Co-doped URhGe up to 30 T prove that this unconventional behavior of the superconductivity (SC) is associated with a strong anisotropy of field-dependent quantum fluctuations near a tricritical point. These fluctuations are rapidly suppressed by the field component along the $$c$$ axis, while being unaffected by any field component along the $$a$$ axis. The observed close interplay between the SC and quantum fluctuations strongly supports a pairing mechanism mediated by these fluctuations in URhGe.

Journal Articles

$$^{29}$$Si NMR spin-echo decay in YbRh$$_2$$Si$$_2$$

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Hattori, Taisuke; Lapertot, G.*; Matsuda, Tatsuma*; Knebel, G.*; Flouquet, J.*; Walstedt, R. E.*

Journal of Physics; Conference Series, 683(1), p.012006_1 - 012006_7, 2016/02


 Times Cited Count:1 Percentile:60.83

By means of nuclear magnetic resonance (NMR) spin-lattice relaxation time ($$T_1$$) measurements on a single crystal sample YbRh$$_2$$Si$$_2$$, the magnetic excitations around quantum critical phase transition is investigated. It is revealed that the coexisting Fermi and non-Fermi states appears near the quantum critical phase transition. Such a mottled state is considered to have remained hidden in Ce and U heavy fermion compounds, owing presumably to short lifetimes for the two states. The mottled state is highly anisotropic to applied magnetic field, which is consistent with previous studies. The origin of mottled state will be discussed.

Journal Articles

Mottled electronic state near a quantum critical phase transition

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo

Nihon Butsuri Gakkai-Shi, 71(1), p.22 - 26, 2016/01

By means of nuclear magnetic resonance (NMR) spin-lattice relaxation time measurements on a single crystal YbRh$$_2$$Si$$_2$$ sample, it is revealed that the coexisting Fermi and non-Fermi states appears near the quantum critical phase transition. Such a mottled state has remained hidden in Ce and U heavy fermion compounds, owing presumably to short lifetimes for the two states. Valence and magnetic instabilities are considered to occur at the same time around the quantum critical phase transition.

330 (Records 1-20 displayed on this page)