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Journal Articles

Resonant X-ray magnetic diffraction experiments on SmB$$_2$$C$$_2$$

Inami, Toshiya; Homma, Tetsuo*; Tsutsui, Satoshi*; Indo, Kentaro*; Onodera, Hideya*; Ishii, Kenji; Owada, Kenji; Kuzushita, Kaori*; Nakao, Hironori*; Murakami, Yoichi*

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.748 - 750, 2007/03

We investigated successive phase transitions in SmB$$_2$$C$$_2$$ at $$T_{rm N2}$$=37K and $$T_{rm N1}$$=51K by means of resonant X-ray diffraction. Strong resonant diffraction signal is observed at the 101 reflection below $$T_{rm N2}$$ at the Sm $$L_3$$ edge, whereas in the intermediate phase signals appear at incommensurate positions $${vec Q}$$=(1$$pmdelta$$, $$pmdelta$$,1) where $$delta$$=0.13. Accordingly, the successive phase transitions in SmB$$_2$$C$$_2$$ is found to be commensurate-to-incommensurate magnetic phase transitions.

Journal Articles

Fractal dimension in percolating Heisenberg antiferromagnets

Ito, Shinichi*; Kajimoto, Ryoichi; Adams, M. A.*; Bull, M. J.*; Iwasa, Kazuaki*; Aso, Naofumi*; Yoshizawa, Hideki*; Takeuchi, Tetsuya*

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.1549 - 1551, 2007/03

We investigated static and dynamical properties in the three-dimensional percolating Heisenberg antiferromagnets, RbMn$$_c$$Mg$$_{1-c}$$F$$_3$$, with the magnetic concentration close to the percolation threshold, $$c_P = 0.312$$, around the superlattice point well below $$T_N$$. In neutron diffraction experiment, the wave number dependence of the elastic scattering component was well fitted to $$q^{-x}$$. Magnetic fractons were also studied using inelastic neutron scattering, and the observed fractons showed the dispersion relation of $$q^z$$. The determined exponents, $$x = 2.43 pm 0.05$$ and $$z = 2.5 pm 0.1$$, were in good agreement with the fractal dimension ($$D_f = 2.48$$).

Journal Articles

Magnetic penetration depth and self-induced irradiation effects in superconducting PuCoGa$$_5$$ probed by muon spin rotation

Oishi, Kazuki; Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Bauer, E. D.*; Morales, L. A.*; Sarrao, J. L.*; MacLaughlin, D. E.*; Shu, L.*; Ito, Takashi; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.566 - 568, 2007/03

no abstracts in English

Journal Articles

NMR observation of quadrupolar order parameter in NpO$$_2$$

Tokunaga, Yo; Aoki, Dai*; Homma, Yoshiya*; Kambe, Shinsaku; Sakai, Hironori; Ikeda, Shugo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Shiokawa, Yoshinobu*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.735 - 737, 2007/03

In this paper, we present recent and detailed $$^{17}$$O-NMR results obtained in a single crystal. From the analysis of the field-angle dependence of the NMR spectrum,the appearance of a hyperfine interaction with field-induced antiferro-octupole (AFO) moment has been confirmed. This field-induced AFO moment appears as a result of the longitudinal triple-$$vec{q}$$ antiferro-quadrupole (AFQ) structure in the ordered state. We have also observed spin echo modulations caused by quadrupole interactions between the $$^{17}$$O nuclei and the Np-5f quadrupole moments. This reveals that the AFQ structure is directly observable by NMR. Our NMR results provide further insight into the microscopic nature of multipole phase transitions in f-electron systems.

Journal Articles

NMR/NQR study of the quadrupole orders in binary uranium-palladium intermetallic compound

Fujimoto, Tatsuya; Haga, Yoshinori; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Onuki, Yoshichika*

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.746 - 747, 2007/03

UPd$$_3$$ shows the successive quadrupole orders at $$T_{rm Q0}=7.5$$ K, $$T_{rm Q1}=6.8$$ K and $$T_{rm Q2}=4.5$$ K. The phase transition at $$T_{rm Q0}$$ comes from the (1/2,0,1/2)-type quadrupole orders on quasi-cubic uranium-sublattice. On the other hand, the quadrupole states below $$T_{rm Q1}$$ are still controversial; while the Polarized Neutron Diffraction suggested the triple-$$q$$ structure, the Resonant X-ray Scattering assumed the canted quadrupole order. In addition, below $$T_{rm Q2}$$, an antiferromagnetic order has been suggested, but the magnetic structure and so on are not still identified. To investigate the local symmetry of the quadruple order in UPd$$_3$$, we tried the nuclear quadrupole resonance, and we succeeded to find the first spin-echo signals from the UPd$$_3$$ probed by $$^{105}$$Pd nuclei. In this paper, we report the nuclear properties of $$^{105}$$Pd isotope and discuss the characteristics of the quadrupole orders emerging in each temperature phases.

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

Parisi function for the ising spin glass in cluster approximations

Yokota, Terufumi

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.e518 - e519, 2007/03

The Ising spin glass is investigated close to the spin glass transition temperature. Parisi's order parameter function and the de Almeida-Thouless (AT) line are obtained in various cluster approximations. A class of cluster approximations introduced by Baviera, Pasquini, and Serva, the Bethe approximation and cactus approximations are used to study effects of fluctuations on the replica symmetry breaking. Fluctuations seem to cause reduction in the slope of the order parameter function. The locus of the AT line for a cluster approximation changes from that for the Sherrington-Kirkpatrick (SK) model and the change seems to be affected by the existence of a loop in a cluster.

Journal Articles

Magnetic property of a single crystal UCu$$_2$$Ge$$_2$$

Matsuda, Tatsuma; Haga, Yoshinori; Ikeda, Shugo; Yamamoto, Etsuji; Onuki, Yoshichika

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.422 - 424, 2007/03

We succeeded in growing a single crystal of UCu$$_2$$Ge$$_2$$ with the tetragonal crystal structure by the Sn-flux method and measured the temperature dependence of electrical resistivity, magnetization and magnetic susceptibility. UCu$$_2$$Ge$$_2$$ orders ferromagnetically below $$T_{rm C}$$ = 109 K. The magnetic properties are highly anisotropic. An easy-axis of the magnetization is found to be the [001] direction(c-axis), while the [100] direction (a-axis) corresponds to the hard-axis in magnetization, indicating Ising-type ferromagnetism. The saturation moment is determined as 1.75$$mu$$$$_{B}$$/U.

Journal Articles

Effect of Hund's rule coupling on SU(4) spin-orbital system

Onishi, Hiroaki; Hotta, Takashi

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.790 - 792, 2007/03

By using a density-matrix renormalization group method, we analyze a one-dimensional spin-orbital model, which is derived from an SU(4) symmetric Hubbard model perturbed by the Hund's rule coupling $$J$$. At $$J$$=0, both spin and orbital correlations have a peak at $$q$$=$$pi$$/2 in the ground state due to the SU(4) singlet state with a four-site periodicity. On the other hand, for large values of the Hund's rule coupling, it is found that the peak position of orbital correlation changes to $$q$$=$$pi$$, while that of spin correlation remains at $$q$$=$$pi$$/2.

Journal Articles

Superconductivity in f-electron systems controlled by crystalline electric fields

Kubo, Katsunori; Hotta, Takashi

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.572 - 574, 2007/03

To elucidate the mechanism and controlling parameter of the superconductivity in CeTIn$$_5$$ (T=Co, Rh, and Ir), we study an $$f$$-electron model based on a $$j$$-$$j$$ coupling scheme on a square lattice. In this study, we consider electrons with total angular momentum $$j$$=5/2. These states split into one $$Gamma_6$$ and two $$Gamma_7$$ doublets under a tetragonal CEF. By choosing appropriate CEF potential, we can control the CEF wave-functions without changing the level splitting. Although the Fermi surface does not change so much as long as the splitting is fixed, the ground state changes depending on the CEF wave-function among paramagnetic, antiferromagnetic, and $$d$$-wave superconducting states. Thus, in addition to the Fermi-surface topology and the carrier density, the wave-function of the CEF state is an important ingredient to control the appearance of superconductivity in such systems. We will discuss possible relevance of our scenarioto the superconductivity in CeTIn$$_5$$.

Journal Articles

Development of a hybrid-anvil type high-pressure device and its application to magnetic neutron scattering studies

Osakabe, Toyotaka; Kakurai, Kazuhisa; Kawana, Daichi*; Kuwahara, Keitaro*

Journal of Magnetism and Magnetic Materials, 310(2, Part3), p.2725 - 2727, 2007/03

no abstracts in English

Journal Articles

Enhancement of relaxation rates in the normal state of superconductor PuRhGa$$_5$$:NQR relaxation study

Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.e118 - e119, 2007/03

The spin-lattice relaxation rates ($$1/T_1$$) have been measured under zero fieldusing nuclear quadrupole resonance (NQR) linesin superconductor PuRhGa$$_5$$ and Pauli-paramagnet LuCoGa$$_5$$. In the reference LuCoGa$$_5$$ with fully-occupied $$4f$$ shell, the $$1/T_1$$ shows the constant behavior of $$(T_1T)^{-1}=0.495pm0.002$$ (sec$$cdot$$K)$$^{-1}$$. On the other hand, in PuRhGa$$_5$$, $$1/T_1$$ is much larger than in LuCoGa$$_5$$and the $$1/T_1propto T$$ behavior below $$sim$$30 K is seen, where its $$(T_{1}T)^{-1}$$ value is 3.27 $$pm$$ 0.005 (sec$$cdot$$K)$$^{-1}$$. These results suggest a development of coherent Fermi liquid stateincorporated with $$5f$$ electronsbelow $$sim$$30 K in PuRhGa$$_5$$.

Journal Articles

Magnetic structural characterization of Mg-Co-Cr ferrite by neutron diffraction

Yunus, S. M.*; Yamauchi, Hiroki; Zakaria, A. K. M.*; Igawa, Naoki; Hoshikawa, Akinori; Ishii, Yoshinobu

Journal of Magnetism and Magnetic Materials, 310(2, Part3), p.2722 - 2724, 2007/03

 Times Cited Count:2 Percentile:12.76(Materials Science, Multidisciplinary)

Temperature dependent neutron diffraction studies were done on the spinel oxide system Mg$$_x$$Co$$_{1-x}$$Cr$$_x$$Fe$$_{2-x}$$O$$_4$$ ($$x=0.0$$, 0.25, 0.50, 0.75 and 1.0). Neutron diffraction data recorded in the temperature range 10,$$-$$,810 K were analyzed in the Rietveld method. Ordered sublattice magnetic moments of the five compositions of the spinel series at various temperatures were deduced from the analysis. A decreasing ordered moment with increasing substitution ($$x$$) was found indicating a gradual weakening of ferrimagnetic order. Huge diffuse signals around the 1,1,1 Bragg diffraction peak were found in the neutron patterns of the composition $$x$$,=,1.0 below the Curie temperature manifesting a build-up of short-range magnetic spin clusters. The observed features suggest a canted ferrimagnetic structure in the composition range $$x$$,$$leq$$,0.75 and a semi-spin glass like transition at $$x$$,=,1.0.

Journal Articles

Resonant X-ray scattering of PrRu$$_4$$P$$_{12}$$

Ishii, Kenji; Tsutsui, Satoshi*; Hao, L.*; Hasegawa, Tomoo*; Iwasa, Kazuaki*; Tsubota, Masami; Inami, Toshiya; Murakami, Yoichi*; Saha, S. R.*; Sugawara, Hitoshi*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.e178 - e180, 2007/03

PrRu$$_4$$P$$_{12}$$ shows a metal-insulator (MI) transition at $$T_{mathrm MI} simeq$$ 62 K accompanied by a structural phase transition. Because LaRu$$_4$$P$$_{12}$$ without $$4f$$ electrons does not shows the MI transition, $$4f$$ electrons in the Pr atom plays an important role in the transition. In order to elucidate a modulation of electronic states of Pr, we have carried out a resonant X-ray scattering study of PrRu$$_4$$P$$_{12}$$ at Pr $$L_2$$- and $$L_3$$-edges. Below $$T_{mathrm MI}$$, resonant signal at the absorption main-edge was successfully observed at the superlattice reflections of the modulation vector $$vec{q}=(1,0,0)$$ in addition to the energy-independent component from the lattice distortion. Because the reflection contains the difference of anomalous scattering factors between two Pr atoms in the unit cell, two different electronic states are actually ordered below $$T_{MI}$$. Furthermore we found that the polarization of X-ray is mostly unrotated even at the resonance, which indicates that the resonant scattering in PrRu$$_4$$P$$_{12}$$ is almost isotropic.

Journal Articles

AC calorimetry study on the pressure-induced superconductor UIr

Tateiwa, Naoyuki; Haga, Yoshinori; Yamamoto, Etsuji; Matsuda, Tatsuma; Ikeda, Shugo; Onuki, Yoshichika*

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.637 - 639, 2007/03

We have measured the heat capacity of the pressure-induced superconductor UIr by ac calorimetry under pressures up to 1.6 GPa. The heat capacity shows an anomaly at the Curie temperature $$T_{rm C1}$$, and this anomaly shifts to lower temperatures with increasing pressure. The present pressure dependence of $$T_{rm C1}$$ was consistent with the results obtained by the previous resistivity and magnetization measurements.

Journal Articles

Microscopic aspects of multipole properties of filled skutterudites

Hotta, Takashi

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.1691 - 1697, 2007/03

In order to develop a theory for multipole phenomena in $$f$$-electron materials, we have proposed the construction of a microscopic model for $$f$$-electron systems based on a $$j$$-$$j$$ coupling scheme. By this approach, magnetism and superconductivity of filled skutterudites have been discussed from a microscopic viewpoint. In particular, we can also evaluate physical quantities related to multipoles by treating them as combined spin and orbital degrees of freedom. In this presentation, we will discuss three issues: (1) A concept of optimal multipole susceptibility to clarify the low-temperature properties of filled skutterudites. (2) An effective way to include the crystalline electric field potential of $$T_{rm h}$$ symmetry of filled skutterudites in the $$j$$-$$j$$ coupling scheme. (3) Dynamical Jahn-Teller effects on multipole properties of filled skutterudites.

Journal Articles

Transport properties in the ferromagnet UTeS

Ikeda, Shugo; Sakai, Hironori; Matsuda, Tatsuma; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu*; Haga, Yoshinori; Onuki, Yoshichika*

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.1718 - 1720, 2007/03

no abstracts in English

Journal Articles

Knight shift measurements in the superconducting state of Pr$$_{1-x}$$La$$_x$$Os$$_4$$Sb$$_{12}$$ (X=0.4) probed by $$mu$$SR

Higemoto, Wataru; Aoki, Yuji*; Oishi, Kazuki; Ito, Takashi; Heffner, R. H.; Saha, S. R.*; Koda, Akihiro*; Sato, Hideyuki*; Kadono, Ryosuke*; Kikuchi, Daisuke*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.620 - 622, 2007/03

no abstracts in English

Journal Articles

Electronic structure and magnetism of CaMn$$_{1-x}$$Ru$$_{x}$$O$$_{3}$$ thin films

Terai, Kota; Yoshii, Kenji; Takeda, Yukiharu; Fujimori, Shinichi; Saito, Yuji; Owada, Kenji; Inami, Toshiya; Okane, Tetsuo; Arita, Masashi*; Shimada, Kenya*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.1070 - 1072, 2007/03

We have studied the electronic and magnetic properties of epitaxially grown CaMn$$_{1-x}$$Ru$$_{x}$$O$$_{3}$$ (x = 1.0, 0.5) thin films by X-ray magnetic circular dichroism (XMCD) and hard X-ray photoemission spectroscopy (HXPES). The XMCD studies indicated that the spin moments of Mn and Ru are aligned in the opposite directions. The HXPES spectra indicated the Ru 4d states at around the Fermi edge (E$$_{F}$$) and the Mn 3d states below E$$_{F}$$. From these results, we propose that the localized Mn 3d t$$_{2g}$$ states and the itinerant Ru 4d t$$_{2g}$$ band are antiferromagnetically coupled and give rise to ferromagnetism, in analogy with the mechanism proposed for the double perovskite oxides such as Sr$$_{2}$$FeMoO$$_{6}$$.

Journal Articles

Magnetic property of neptunyl (+2) complex NpO$$_{2}$$(C$$_{6}$$H$$_{7}$$O$$_{2}$$)$$_{2}$$(C$$_{5}$$H$$_{5}$$N)

Nakamura, Akio; Nakada, Masami; Nakamoto, Tadahiro*; Kitazawa, Takafumi*; Takeda, Masuo*

Journal of Magnetism and Magnetic Materials, 310(2, Part2), p.1447 - 1449, 2007/03

Magnetic property of a nitrogen (N)-coordinated neptunyl (+2) (Np(VI)) complex. 1 NpO$$_{2}$$(acac)$$_{2}$$(py) (acac=C$$_{6}$$H$$_{7}$$O$$_{2}$$, py=C$$_{5}$$H$$_{5}$$N) was studied by DC magnetization (M) measurements. While previous $$^{237}$$Np M$"o$ssbauer data of 1 exhibited para magnetic-relaxation spectra similar to other oxo-neptunyls (+1,+2), the DC-$$M$$ data have revealed many strikingly different features of 1 from the latter: first, its reciprocal susceptibility ($$chi$$$$^{-1}$$) vs. $$T$$(K) plots showed a peculiar strongly field ($$H$$)-dependent nonparamagnetic behavior, which suggests the presence of small ferromagnetic component with $$T$$$$_{C}$$$$>$$300 K. In addition, its low-temperature isothermal $$M$$ exhibited anomalous relaxation behavior involving initial over-responsive $$M$$ change and subs equent drift back to its "equilibrium" value ($$M$$$$_{rm eq}$$). Moreover, such $$M$$$$_{rm eq}$$ showed strong perturbation effect from the SQUID-$$M$$ measurement itself. Such novel magnetic features suggest the presence of a largely metastable fluctuating magnetic (spin plus orbital) state in 1 as a collective body of individual Ising-type neptunyl (O=Np=O)$$^{+2}$$ molecular magnets.

47 (Records 1-20 displayed on this page)