Jung-Hae Park

Raman studies on single-phasic HgBa2CuO4+δ superconductors

Abstract Polycrystalline samples of HgBa 2 CuO 4+δ superconductors were prepared by solid state reaction of HgO and Ba 2 CuO 3+ x precursor in an evacuated silica tube. The HgBa 2 CuO 4+ δ has a T c of 92 K and has a tetragonal cell (P 4/mmm) with lattice parameters a and c with the values of 3.8868 (2) A and 9.4886 (1) A, respectively. Raman spectra of polycrystalline HgBa 2 CuO 4+δ show four peaks at 108 cm −1 , 158 cm −1 , 570 cm −1 and 592 cm −1 . Using a factor group analysis and Raman spectral data of the cuprate superconductors, these modes are assigned as E g and A 1g modes of Ba atoms and O(2) oxygens. The higher peaks at 570 cm −1 and 592 cm −1 are assigned to E g and A 1g modes of O(2) oxygen, respectively. The lower two modes at 108 cm −1 and 158 cm −1 are ascribed to vibrations of Ba atoms. Details of mode assignments are discussed based on symmetry and local structure.

Raman spectra of HgBa2Ca2Cu3O8+d superconductors

Abstract We have measured Raman spectra of HgBa2Ca2Cu3O8+d (Hg-1223) superconductors. The spectra show peaks at 92, 127, 138, 230, 479, 538, 574, and 585 cm-1. From a factor group analysis and the structural information about Hg-1223, we assign the modes at 92, 574, and 585 cm-1 to be A1g modes of Ba, O(2) and O(3) atoms, respectively. The modes at 479 and 538 cm-1 are proposed to be Eg modes of O(3) bending and O(2) stretching vibrations, respectively. Details of mode assignments are given in the discussion.

Infiltration-reaction process for fabricating YBa2Cu3O7−δ superconductor

Abstract A new process for fabricating YBa2Cu3O7−δ superconductor was developed using infiltration-reaction process. A stack of Y2BaCuO5 and YBa2Cu3O7−δ compacts was heated at 1000–1200 °C and then cooled. By the infiltration-reaction process YBa2Cu3O7−δ superconductor where Y2BaCuO5 dispersions under 5 ωm were densely and evenly distributed has been fabricated without residual liquid phase. The resulting YBa2Cu3O7−δ superconductor showed large hysteresis and Jc from magnetization measurement.

A low-noise integrated SQUID gradiometer for biomagnetic sensors

We developed a low-noise and compact SQUID gradiometer for biomagnetic multichannel applications. The SQUID is based on a double relaxation oscillation SQUID and provides very large flux-to-voltage transfer coefficients, allowing simple flux-locked loop electronics to be used for SQUID operation. The pickup coil is a first-order planar gradiometer integrated on the same wafer as the SQUID and has a baseline of 40 mm. The field gradient noise of the SQUID gradiometer in flux-locked loop mode is around 1 fT/cm/spl radic/Hz at 100 Hz, measured inside a magnetically shielded room.

Critical dynamics of superconducting Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ single crystal

The magnetization and resistivity of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ (Bi-2212) single crystals have been measured as a function of magnetic field H and temperature T. The extracted fluctuation part of the magnetization and conductivity exhibit critical behavior consistent with the three dimensional XY model. The dynamic critical exponent z is 1.6/spl plusmn/0.1, which is close to the value for YBCO. The static critical exponent v is 0.769 and 0.909 respectively for the magnetization and conductivity data. The values of v are larger than that of YBCO. The results indicate that the weak interlayer coupling along the c-axis of Bi-2212 does not influence the dynamic critical exponent z but significantly increases the static critical exponent v.

Magnetization and flux creep in YBa2Cu3Ox superconductor prepared by infiltration-reaction process

Abstract Magnetization and flux creep have been investigated in YBa 2 Cu 3 O x superconductor fabricated by infiltration-reaction process. The YBa 2 Cu 3 O x sample including fine Y 2 BaCuO 5 particles was prepared by infiltrating the liquid of YBa 2 Cu 3 O x into Y 2 BaCuO 5 compact at 1030 °C for 30 min. Experimental results of the temperature dependence of magnetization and the magnetization hysteresis showed that there was the enhancement of flux pinning in the sample. From the flux creep measurement, 0.55 eV of pinning energy was obtained.

Superconducting properties versus oxygen content in a Sr-doped HgBa2Ca1−xSrxCu2O6+δ

Abstract Polycrystalline samples of HgBa2Ca1−xSrxCu2O6+δ were prepared by solid state reaction of HgO, Ba2CuO3+δ and Ca1−xSrCuO2 (x=0.14) in an evacuated silica tube. The as-synthesized sample has a Tc of 120 K and has tetragonal symmetry ( P4 mmm ) with lattice parameters of a =3.8584(1) A and c =12.6646(5) A . After annealing under O2 at 250 °C for 8 h, the Tc was enhanced to 124 K. The content of oxygen uptakes is about 0.11, which was estimated by a TGA analysis. However, the X-ray powder diffraction data and the Raman spectra of both as-synthesized and oxygen-annealed samples did not show any substantial difference.