Izumi Tomeno

63Cu(2) nuclear spin-spin relaxation in YBa2Cu3O6.98, YBa2(63Cu)3O7-δ, and YBa2Cu4O8

We have measured the temperature dependence of the transverse relaxation time of 63 Cu(2) nuclear spin in YBa 2 Cu 3 O 6.98 , YBa 2 ( 63 Cu) 3 O 7 , and YBa 2 Cu 4 O 8 . After subtraction of the T 1 process, the decay curve of the spin-echo envelope for YBa 2 Cu 4 O 8 in a strong H 1 followed a single Gaussian form from 280 K to 4.2 K, while for YBa 2 Cu 3 O 6.98 it follows only above T c . The absolute value and the temperature dependence of the decay rate 1/ 63 T G could be understood by the combined contributions of the direct dipole-dipole and the temperature-dependent indirect nuclear spin-spin coupling via χ( q ). From the temperature dependence of 1/ 63 T G for YBa 2 Cu 4 O 8 below T c , we considered that χ( Q ) even below T c remains enhanced. In a viewpoint of the 63 Cu(2) nuclear spin-spin relaxation experiments, so far as YBa 2 Cu 4 O 8 is concerned, the high- T c superconductivity seems to exhibit the d -wave pairing.

Nuclear spin-lattice relaxation and Knight shift in YBa2Cu4O8

Abstract The temperature dependences of the 63Cu nuclear spin-lattice relaxation rate 1/T1 and Knight shift K in YBa2Cu4O8 have been measured by nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) techniques. In the normal state, both the 1 T 1 for the Cu(2) sites and the in-plane component of the Knight shift K2⊥ increase rapidly with temperature from Tc up to about 250 K. Approximate T-linear temperature dependence of 1 T 1 was observed in a wide temperature range between 250 and 680 K, that is in general accord with previous analyses.

Elastic and Dielectric Properties of LiNbO3

Elastic constants C 11 , C 33 , C 44 , and C 66 , and dielectric susceptibilities χ 11 and χ 33 in LiNbO 3 , were determined over the temperature range from 300 to above 1030 K. The elastic-constant difference between constant polarization and constant field \(C^{P}_{\imath\imath}-C^{E}_{{\imath}i}\), and the inverse-susceptibility difference between constant strain and constant stress\((\chi^{x}_{i{\imath}})^{-1}-(\chi^{X}_{\imath\imath})^{-1}\) are interpreted in terms of both electrostrictive and higher-order interaction between strain and polarization. The results for χ 33 indicate that LiNbO 3 undergoes nearly second-order phase transition at T C =1410 K. Above T C , χ 33 showed dispersion in the frequency range between 1 and 13 MHz. A comparison of these results with soft-mode frequency implies that the soft mode couples with a low frequency relaxation process near T C .

Magnetic neutron scattering study of ordered Mn3Ir

Neutron-diffraction measurements were made on an ordered Mn3Ir single crystal in a wide temperature range up to 1030 K. The ordered Mn3Ir alloy was found to maintain an antiferromagnetic (AF) triangular spin structure up to the Neel temperature TN=960±10 K. The lattice parameter a shows a continuous change in the temperature range including TN. In contrast to the isostructural ordered Mn3Pt alloy, these observations indicate that an AF–AF phase transition is absent in the ordered Mn3Ir alloy.

Single crystal growth and characterization of Bi2Sr2Ca1-xYxCu2Oy by TSFZ method

Abstract Single crystals of Bi2Sr2Ca1−xYxCu2Oy were grown by means of the Traveling Solvent Floating Zone (TSFZ) method. Several single crystals with an average size of 0.5mm×2mm× 10μm were obtained by cleaving the boules. Observation by EPMA shows that the ab-plane of the samples are smooth and of single phase. X-ray diffraction data show that the lattice constant along the c-axis decreases with increasing the Y content as reported for sintered materials.

Carrier concentration dependences of the nuclear spin-lattice relaxation rate and the Knight shift in Y1−xCaxBa2Cu4O8

Abstract The temperature dependences of the 63 Cu nuclear spin-lattice relaxation rate T 1 -1 and the Knight shift K ab at the planar Cu(2) site in Ca substituted YBa 2 Cu 4 O 8 have been measured by the nuclear quadrupole resonance (NQR) and the nuclear magnetic resonance (NMR) techniques. The notation “ ab ” means that the external field is perpendicular to the c -axis. The temperature dependence of K ab in the Ca substituted sample becomes weaker compared with the non-substituted sample, indicating that the electronic state in the CuO 2 plane turned more metallic with Ca substitution. On the other hand, ( T 1 T ) -1 in the non-substituted sample increased rapidly with increasing temperature and showed a maximum value at 160 K, the so-called spin-gap temperature, T S . Subsequently, ( T 1 T ) -1 decreased with increasing temperature above the spin-gap temperature as in the Curie-Weiss law. While the behaviors of ( T 1 T ) -1 in Ca substituted samples were similar to that in the non-substituted YBa 2 Cu 4 O 8 , the spin-gap temperature decreased with increasing Ca (hole carrier) content. From the decrease of T S with the carrier concentration, we conclude to the existence of a negative linear relation between the spin-gap temperature and the superconducting transition temperature.

Lattice Dynamics of Disordered Perovskite Pb(Zn1/3Nb2/3)O3

Inelastic-neutron-scattering experiments were performed to investigate the phonon-dispersion relations in the cubic relaxor Pb(Zn 1/3 Nb 2/3 )O 3 . The transverse acoustic (TA) phonon branches have flat and isotropic dispersion curves. The zone-boundary [ζζ0]-TA 2 phonon energy is approximately 6 meV, considerably lower than the values reported for simple perovskites. The low-lying transverse optical (TO) branches drop sharply with decreasing ζ, similar to the behavior observed for the complicated system Pb(Zn 1/3 Nb 2/3 ) 0.92 Ti 0.08 O 3 . The constant- Q scans reveal the absence of the well-defined TO phonon spectra in the range 0≤ζ≤0.1, in contrast with the sharp TA spectra. The TA, TA 2 and TO phonon energies at ζ=0.1 and 0.2 decrease with increasing temperature up to 673 K. The phonon hardening toward the transition temperature contradicts the usual soft mode behavior in simple perovskites.

Relaxor as heterophase fluctuation

Abstract A neutron diffuse scattering experiment on the relaxor ferroelectric PZN(PbZn1/3Nb2/3O3) has been carried out. The diffuse scatterings show strongly anisotropic distributions around the reciprocal lattice points, whose patterns change drastically depending on the index of the reciprocal lattice point. These experimental results are analyzed based on the G-L type free energy functional including electrostrictive energy. It is verified that the observed diffuse scattering is due to the strain field produced by polar micro clusters which are characterized as the heterophase fluctuations of polarization.

Ultrahigh vacuum STM/STS studies of the Bi-O surface in Bi2Sr2CuOy single crystals

Abstract Scanning tunneling microscopic and spectroscopic studies were made on cleaved of Bi 2 Sr 2 CuO y single crystals using an ultrahigh-vacuum scanning tunneling microscope (UHV-STM). The modulation structures of the BiO surface were observed at room temperature with atomic resolution. The tunneling spectra showed electronic gap structures similar to those observed for the BiO surface of superconducting Bi2212 single crystals. This suggests that superconductivity is not directley related to the electronic structure observed in the BiO plane.

Dynamical Spin Susceptibility and Bi-Layer Coupling in YBa2Cu4O8

We have extracted the T -dependence of the dynamical susceptibility at q ∼0 and q ∼ Q from the spin-lattice and the spin-spin relaxation measurements at the Cu and O sites in the normal state of YBa 2 Cu 4 O 8 . The estimated dynamical susceptibility suggests that the relation of T 1 T K spin =const does not hold around q =0. We have measured the temperature ( T )-dependence of the Knight shift and the spin-lattice relaxation time at the Y site in the same sample. Based on the comparison between the observed T -dependence of T 1 at the Y site and the calculated one using the extracted single layer dynamical susceptibility, we have suggested the development of the singlet or antiferromagnetic bi-layer coupling in the YBa 2 Cu 4 O 8 .