Akihiko Hisada

Fabrication and efficiency evaluation of a hybrid NiCrAl pressure cell up to 4 GPa

A hybrid NiCrAl pressure cell was fabricated to measure magnetic quantities under high pressure above 3 GPa. A pressure of 4.0 GPa was achieved and the pressure cell was found to be reusable even after a pressurizing trial up to 4.0 GPa. Pressure was monitored using (63)Cu nuclear quadrupole resonance of Cu(2)O and ruby fluorescence. The pressure efficiency of a fresh cell was maintained at 96%, and no appreciable deformation was observed at pressures below 3 GPa; on the other hand, the efficiency after pressurizing trials decreased gradually and reached 75% at 4 GPa accompanied by a maximum expansion inside the cylinder of 2%.

Superconductivity on a Crossover Phenomenon of Spin–Ladder System SrCa13Cu24O41 Single Crystals

Electrical resistivity and alternating current susceptibility measurements were performed for the spin–ladder compound SrCa13Cu24O41 under hydrostatic pressure up to 8 GPa. The superconducting transition was observed below TC = 14.7 K at pressures above 2 GPa. By using high-quality single crystals, the bulk superconductivity with a volume fraction of 50% and temperature quadratic behavior of the normal state resistivity were observed above 3.7 GPa. They suggest that a strong interladder interaction induces the bulk superconductivity and transforms the system into a Fermi-liquid-like state. The optimal pressure was in a crossover region and the highest TC was observed without going through the bulk superconducting state. Our results suggest that the superconducting state on the crossover phenomenon presents the feature of the doped two-leg spin–ladder system because the spin gap was observed in this compound.

Fabrication of a NiCrAl pressure cell and the application to a two-leg ladder compound Sr2Ca12Cu24O41

A hybrid NiCrAl pressure cell was fabricated to measure magnetic quantities above 3 GPa. A pressure of 4 GPa was achieved and the pressure cell was found to be reusable even after pressurizing trial up to 4GPa. The inner diameter of the cylinder expanded 2.5% at 4 GPa. The pressure cell was applied to the 63Cu-NMR measurement at an optimum pressure of 3.8 GPa in a pressure-induced superconductor Sr2Ca12Cu24O41.

The effect of pressure on the nuclear quadrupole resonance and ruby fluorescence in a NiCrAl pressure cell

A pressure of 4.0 GPa was achieved using a piston-cylinder-type NiCrAl pressure cell which possesses a large sample space of 4.4 mm diameter x 15 mm length at ambient pressure. As monitors of the pressure, the 63 Cu nuclear quadrupole resonance (NQR) of Cu 2 O and ruby fluorescence were studied at the same time. The relation between the NQR frequency and the R1 line of the ruby fluorescence was investigated at pressures below 3.2 GPa.

Nuclear magnetic relaxation in a quasi-one-dimensional conductor β-Ag0.33V2O5

51V nuclear-magnetic-resonance (NMR) measurements were performed on β-Ag0.33V2O5, a quasi-one-dimensional conductor with three crystallographically inequivalent V sites (V1, V2, and V3). We observed the site difference between the V1 and V2 sites. The nuclear quadrupole frequency (νQ) shows different temperature dependence between the V1 and V2 sites, and the values of the relaxation rate (1/T1) are also different between the two sites in the metallic phase. These facts suggest that a non-uniform metallic state is realized: a 3d electron shared within a V1–V3 or V2–V2 rung in the CO phase could move in the quasi-one-dimensional direction in the metallic phase.

Local Electric Properties of β-Ag0.33V2O5 Studied by 51V NMR

The local electric properties of β-Ag 0.33 V 2 O 5 , a pressure-induced superconductor, were studied at ambient pressure using a nuclear magnetic resonance (NMR) technique. Three crystallographically inequivalent V i sites ( i =1, 2, and 3) were identified from 51 V-NMR spectra. We determined the principal axes of the electric-field-gradient (EFG) tensor, electric quadrupole frequency, asymmetric parameter, and Knight shift for each V i site in the metallic phase and the subsequent charge-ordering (CO) phase at low temperatures. The results suggest that the electric properties for the V1 sites are similar to those for the V3 sites, whereas those for the V2 sites are different from those for the V1 and V3 sites. The peculiarity in the metallic phase reflects the electric properties in the CO phase and is attributable to the diagonal structure of the V i orbitals.