Aa Gippius

The relaxation of the monodomain TmBa2Cu3Ox single crystal magnetization in the superconducting state

Abstract Measurements of the remanent magnetization relaxation RM ( t ) in the monodomain TmBa 2 Cu 3 O x single crystal are reported. The relaxation rate r ( T ) = d RM ( T , t )/d(ln t ) has a sharp maximum at temperature T = T max . The T max value is about 15 K for H = 2.8 kOe and it strongly depends on the magnitude of the applied magnetic field being shifted to higher temperatures as H is decreased. The normalized rate r ( T )/ RM 0 in contrast to the r ( T ) behavior, is almost isotropic irrespective of the H direction. The r ( T ) maximum is qualitatively reproduced by the calculation taking into account the thermal activated flux creep and Abrikosov vortices distribution according to the Bean model.

Bi-based superconductors and their surface wave velocities

Abstract We have measured the surface hypersound velocity values VR of Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 single crystals by Mandelstamm-Brillouin light scattering spectra. Measurements were performed at room temperature. In case of Bi2Sr2CaCu2O8 crystal considerable difference (20%) of (001) plane VR values along a and b crystallographic directions was manifested. However mentioned VR anisotropy in Bi2Sr2CuO6 crystals was not observed.

EPR spectra in R2BaCuO5 (R=Y, Sm, Eu, Gd, Dy, Ho) oxides

Abstract We studied temperature dependencies (4÷300 K ) of EPR spectra in R 2 BaCuO 5 (R=Y, Sm, Eu, Gd, Dy, Ho) single crystals and ceramics. When R 3+ is nonmagnetic the Cu 2+ ( S = 1 2 ) EPR signal is absent at room temperatures. We computed the (3d) 9 and (3d) 8 configurations crystal field splitting using the ligand field theory. In Gd 2 BaCuO 5 single crystals the anisotropy of resonance field and line width with the 120° period has been observed.

Possible intermediate Jahn-Teller EPR spectra in RBa2Cu3O7−x (R=Sm, Tm) single crystals

Abstract Superconducting (Tc≈80 K) single crystals RBa 2 Cu 3 O 7− x (R123) with R=Sm, Tm were studied at 4÷300 K by EPR. At room temperature spectra are almost isotropic with g=2.10 (2). Significant spectra transformation occurs below 7 K. The Sm123 spectra at 4 K can be approximated by at least three lines: an isotropic line with g≈2.10 (2), Δ H =220 Oe and two less intense anisotropic lines with g≈1.96, Δ H =55 Oe and g≈2.33, Δ H =100 Oe, respectively. The observed transition seems to be caused by the crossover from the dynamic to the intermediate Jahn-Teller (JT) effect.