K Magishi

Superconducting Characteristics of Filled Skutterudites LaPt4Ge12 and PrPt4Ge12: 73Ge-NQR/NMR Studies

We report on the superconducting characteristics of the filled skutterudites LaPt 4 Ge 12 ( T c =8.3 K) and PrPt 4 Ge 12 ( T c =7.9 K) by 73 Ge-nuclear quadrupole resonance (NQR) at a zero field. In PrPt 4 Ge 12 , the nuclear spin–lattice relaxation rate 73 (1/ T 1 ) has revealed a coherence peak just below T c , indicating that the superconductivity of PrPt 4 Ge 12 is accounted for in terms of the conventional BCS regime. The result was consistently reproduced by not only an isotropic s -wave gap model but also an anisotropic s -wave gap model with a point node. In the conventional superconductor LaPt 4 Ge 12 , the coherence peak in 73 (1/ T 1 ) is markedly suppressed owing to some damping effect of quasiparticles. We note that the T c s of LaPt 4 Ge 12 and PrPt 4 Ge 12 being higher than that of other R Pt 4 Ge 12 may be attributed to the larger density of states, not to some local anharmonic phonon modes derived from the possible rattling of R ions.

NMR Study of Layered Transition Metal Ditelluride (Ir,Pt)Te2

We report the results of 125Te and 195Pt NMR measurements on (Ir,Pt)Te2 in order to elucidate the characteristic electronic states. For PtTe2, the NMR spectrum exhibits a sharp line, which shows the uniaxially symmetric powder pattern due to the anisotropic Knight shift. The Knight shift is almost independent of temperature and is larger than that for IrTe2. Also, the nuclear spin-lattice relaxation rate 1/T1 of PtTe2 is proportional to the temperature in a wide temperature range, that is, obeys the Korringa relation as expected for simple metallic systems. From the analyses of the Knight shift and 1/T1, it is suggested that the antiferromagnetic correlations slightly exist.

NMR study of filled skutterudite NdOs4P12

We have succeeded in growing the single crystals of NdOs4P12 and investigated the electrical resistivity, magnetic susceptibility and nuclear magnetic resonance (NMR). NdOs4P12 shows metallic behavior in the electric resistivity and undergoes a ferromagnetic transition at 1.15 K. The Knight shift increases upon cooling, similar to the magnetic susceptibility, and little depends on the magnetic field except for below 10 K. Also, the nuclear spin-lattice relaxation rate divided by temperature 1/T1T is largely enhanced with decreasing temperature, implying the significant development of the magnetic fluctuations. 1/T1T is strongly suppressd by the magnetic field, in contrast to the Knight shift. It suggests the coexistence of the ferromagnetic and antiferromagnetic spin fluctuations, similar to the results for NdRu4P12.

11B NMR study in the tetragonal compound CeB2C2

Abstract We carried out the 11 B NMR experiments of CeB2C2 and determined the parameters of the electric field gradient and the components of the hyperfine coupling tensors at 11 B site in order to elucidate the magnetic properties. The nuclear quadrupole frequency and the asymmetry parameter are estimated to be ν Q =0.78 MHz and η=0.22. The hyperfine coupling tensors are highly anisotropic and are deduced to be A X =+0.39 kOe / μ B and A Y =−0.51 kOe / μ B , where the anisotropic hyperfine coupling can be explained by the atomic dipolar field from the 4f electrons.

31P NMR Study of Filled Skutterudite CeOs4P12

We report the results of the electrical resistivity ρ(T) and the 31P-NMR measurements on filled skutterudite CeOs4P12 in order to investigate the magnetic properties at low temperatures from a microscopic point of view. For the polycrystalline sample synthesized under high pressure (HP), ρ(T) increases with decreasing temperature. On the other hand, for the single crystal (SC), ρ(T) reveals a positive temperature dependence between room temperature and 200 K, and increases with decreasing temperature below 200 K. Also, 1/T1 obeys the activated temperature dependence 1/T1 ∝ exp(−Δ/kBT) above 160 K with an energy gap Δ/fB ~ 500 K and 540 K for the HP and the SC samples, which are slightly larger than that of a previous report.

73Ge NQR Study of Superconducting Skutterudites MPt4Ge12 (M = Sr, Ba)

We report on the results of the 73 Ge-NQR measurements for M Pt 4 Ge 12 ( M = Sr, Ba) to clarify the microscopic electronic states and the relationship between superconductivity and rattling. In the normal state, 1/ T 1 is proportional to temperature, showing a Korringa relation 1/ T 1 T = 0.020 and 0.016 (sK) -1 for SrPt 4 Ge 12 and BaPt 4 Ge 12 , respectively. Also, in the superconducting state, 1/ T 1 shows a distinct coherence peak just below T C , which suggests a conventional BCS superconductor.

Cu NMR and NQR studies on the magnetic order in Sr2.5Ca11.5Cu24O41

Abstract The magnetic order in a single-crystal Sr 2.5 Ca 11.5 Cu 24 O 41 (Ca11.5) was investigated by Cu nuclear magnetic and quadrupole resonance (NMR/NQR) techniques. The magnetic order was found to be three-dimensional (3D). Small moments ∼0.02 μ B are spontaneously ordered on the ladders. Dissociation of hole pairs into single holes which localize below T L ∼60 K is responsible for the manifestation of the spin degree of freedom on the ladders.