J. Igalson

Ferromagnetism of (Pb, Sn, Mn) Te under high pressure

Abstract Results of measurements of the magnetic susceptibility in the p-type diluted magnetic semiconductor [(PbTe)1-x(SnTe)x]1-y(MnTe)y with x = 0.72, y = 0.03 are presented. The temperature of the ferromagnetic ordering Tc increases (for hole concentration 3×1020 cm-3) 7 × 1020 cm-3) as hydrostatic pressure is applied. The pressure causes an increase in the concentration of carriers responsible for the interactions between Mn ions. The observed shift of Tc with pressure is interpreted on the basis of the RKKY interaction mechanism and points out the importance of the band structure behavior in consideration of magnetic properties of the semiconductor.

Magnetic properties of the high Tc superconductor YBa2Cu3O7−δ

Abstract Magnetic measurements have been performed on the YBa 2 Cu 6 O 7−δ superconducting system in the temperature range 4.2–320 K. A hystereris loop indicating a coexistence of the superconducting and magnetic ordering below H c1 at 4.2 K has been recorded.

Tunneling observation of the superconducting energy gap in the palladium hydride thin films

Abstract Superconductivity in hydrogen charged palladium thin films has been studied. Using niobium based tunneling junctions the energy gap in PdHx samples, with different values of x and hence of Tc have been observed.

Tunneling structures of high-Tc superconductors La1.8Sr0.2CuO4 and YBa2Cu3O7−d

Abstract Tunneling characteristics dV/dI vs V of superconducting ceramics La 1.8 Sr 0.2 CuO 4 and YBa 2 Cu 3 O 7-d were measured and discussed in terms of granular superconductivity. The temperature dependences of peaks in dV/dI curves are described.

Raman spectra of the high-Tc superconductor Y-Ba-Cu-O

Abstract The Raman scattering experiments on the high- T c superconducting material Y-Ba-Cu-O have been performed at room temperature. Two strong lines at 600 and 1100 cm -1 have been observed and discussed.

PRESSURE EFFECTS ON NEW HIGH- T c SUPERCONDUCTORS

Abstract The pressure dependence of the superconducting transition temperature T c for La 1.8 Sr 0.2 CuO 4 , YBa 2 Cu 3 O 7-δ and EuBa 2 Cu 3 O 7−δ systems was measured under hydrostatic pressure up to 10 kbar. It is found that T c linearly increases with pressure for the La and Eu based systems. A nonlinear decrease of T c has been observed for the Y system.

Magnetic properties of oxygen-deficient GdBa2Cu3Oy single crystals

Abstract Magnetisation measurements have been performed on a series of GdBa2Cu3Oy crystals with varying oxygen content y = 6.2 − 6.4. The measurements have been done at a temperature range T = 5 − 60 K for two magnetic field orientations: H ⊥ ab and H ⊥ ab. We have observed two contributions to the measured dc magnetisation: a paramagnetic contribution related to the Gd ions and a diamagnetic contribution related to superconductivity with Tc = 26 − 40 K. The diamagnetic contribution is strongly anisotropic. we discuss a possibility of existence of the 2D-type superconductivity in the studied samples. Another possible explanation of our results is an inhomogeneous oxygen distribution in the studied crystals.

Flux trapping in high Tc superconductor single crystals in a tilted magnetic field

Abstract Zero-field-cooled, field-cooled and remanent magnetization of Pb 2 Sr 2 Y 0.3 Ca 0.7 Cu 3 O 8 single crystals has been studied for various orientations between the applied magnetic field and the crystallographic axes. One of the crystals demonstrated a demagnetizing factor that was nearly angle-independent. We therefore separated the material anisotropy from the sample shape anisotropy in our measurements. It is shown that the field-cooled magnetization is independent of the shape of the sample and reflects the anisotropy of the magnetic flux trapping. We observe that the vortices are mostly trapped in the direction parallel to the Cu-O planes. We have found a similar qualitative character of the anisotropy in a YBa 2 Cu 3 O 6 + x crystals. Our results are consisdent with the anisotropy of the irreversibility line observed in high- T c superconductors.

Pressure dependence of Tc in solid solutions of M-Ba-Cu-O (M = Y, Eu, Ho)

Pressure dependence of T c in solid solutions of MBa 2 Cu 3 O x ceramic material have been measured resistively and inductively by means of a.c. magnetic susceptibility. The observed sequence of T c shifts with pressure depends on the chemical formula of the superconducting sample as well as on the method of measurements. It is proposed to treat separately contributions of the interand intea-grain regions to the measured responses.

Influence of annealing on anisotropy of flux trapping in polycrystalline Nb samples

Flux trapping in polycrystalline Nb samples has been studied for various field orientations. Annealing of the Nb samples changes the character of anisotropy of flux trapping, depending on the annealing temperature. It is shown that the anisotropy of flux trapping is a result of the sample geometry as well as of the distribution of defects in the samples. Possible mechanisms of the rearrangement of defects during annealing are discussed.