Ko-ichi Magishi

Antiferro-Quadrupole Ordering of CeB6 Studied by Resonant X-Ray Scattering

Under zero magnetic field, a quadrupolar order parameter at \(\mbi{q}_{Q}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})\) in a typical antiferro-quadrupole (AFQ) ordering compound CeB 6 has been observed f...

Antiferro-quadrupole Ordering of CeB

Under zero magnetic field, a quadrupolar order parameter at \(\mbi{q}_{Q}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})\) in a typical antiferro-quadrupole (AFQ) ordering compound CeB 6 has been observed f...

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We report the results of 121,123 Sb-nuclear quadrupole resonance (NQR) and 139 La-NMR measurements on a filled skutterudite antimonide LaFe 4 Sb 12 in order to investigate the magnetic properties at low temperatures from a microscopic point of view. The nuclear spin–lattice relaxation time T 1 of Sb nuclei deviates from the relation T 1 T = constant above 4.2 K, where 1/ T 1 T has a Curie–Weiss temperature dependence 1/ T 1 T = C /( T +θ) with θ∼30 K. The temperature dependence of the Knight shift of 139 La nuclei, which is related to the susceptibility at q = 0, is scaled to that of 1/ T 1 T above 40 K. This relation strongly suggests that ferromagnetic fluctuations are predominant in LaFe 4 Sb 12 . We also point out that LaFe 4 Sb 12 is situated close to the ferromagnetic instability due to the small Weiss temperature in the Curie–Weiss behavior of 1/ T 1 T and the Knight shift.

Studied by Resonant X-ray Scattering

We have synthesized the polycrystalline samples of Ge-based filled skutterudites R Pt 4 Ge 12 ( R =La, Ce, Pr, Nd) and investigated the lattice constant, electrical resistivity, magnetic susceptibility and nuclear magnetic resonance (NMR) systematically. LaPt 4 Ge 12 is confirmed to be a conventional BCS-type superconductor by the NMR measurements. Additional contribution ascribed to the rattling motion of the La ions has been observed in the nuclear relaxation at the La site at high temperatures. Temperature dependence of the magnetic susceptibility of CePt 4 Ge 12 shows a broad peak around 80 K, which is a typical feature of valence fluctuation systems, whereas PrPt 4 Ge 12 and NdPt 4 Ge 12 show the well-localized nature of 4 f -electrons. The NMR measurements in CePt 4 Ge 12 revealed that the nuclear spin–lattice relaxation rate 1/ T 1 shows an activation-type temperature dependence 1/ T 1 ∝exp (-Δ/ k B T ) with an energy gap Δ/ k B =150 K above 100 K, whereas it is proportional to the temperature belo...

Evidence for Ferromagnetic Fluctuations in Filled Skutterudite LaFe4Sb12:Sb-NQR and La-NMR

We report the results of 87Rb NMR measurements on RbOs2O6, a new member of the family of the superconducting pyrochlore-type oxides with a critical temperature Tc = 6.4 K. In the normal state, the nuclear spin-lattice relaxation time T1 obeys the Korringa-type relation T1T = constant and the Knight shift is independent of temperature, indicating the absence of strong magnetic correlations. In the superconducting state, T1^{-1}(T) exhibits a tiny coherence enhancement just below Tc, and decreases exponentially with further decreasing temperatures. The value of the corresponding energy gap is close to that predicted by the conventional weak-coupling BCS theory. Our results indicate that RbOs2O6 is a conventional s-wave-type superconductor.

Electrical, Magnetic and NMR Studies of Ge-Based Filled Skutterudites RPt4Ge12 (R = La, Ce, Pr, Nd)

Abstract 63 Cu NMR measurements have been carried out in HgBa 2 Ca 2 Cu 3 O 8+δ (Hg1223) with the highest transition temperature, T c = 133 K, to date. The narrow NMR spectrum and the small residual density of states (DOS), N res , at the Fermi level in the superconducting state indicate that the Hg1223 possesses good quality.

Evidence fors-wave superconductivity in theβ-pyrochlore oxideRbOs2O6

Results of our NMR measurements of highTc superconductors are reviewed. From systematic measurements of NQR frequency, Knight shift, nuclear spin lattice relaxation rate and nuclear transverse relaxation rate over a wide hole concentration range from light to heavy doped compounds together with the impurity and pressure effect, following results are concluded. The numbers of the holes at the respective sites of Cu and O site in the CuO2 plane govern the several physical properties of the system. There are optimum values of these hole numbers to produce highestTc. The superconducting properties are well explained consistently by thed-wave pairing model.Tc is found to be correlated intimately with the antiferromagnetic spin fluctuation parameters that governs the nuclear relaxation. The mechanism for the superconductivity is magnetic in origin.

63Cu NMR investigation of HgBa2Ca2Cu3O8+δ

Based on experimental

NMR of highT c superconductors

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Localized versus itinerant magnetic moments in Na0.7CoO2

-NMR data in the temperature range between 0.1 and