V.A. Rybachuk

Temperature dependences of lower critical fields in TmBa2 Cu3O7−x single-crystals

Abstract Temperature dependences of lower critical fields Hc1 of the monodomain single crystals TmBa2 Cu3 O7−x were measured for different magnetic fields orientations with respect to the crystallographic axes. The linear Hc1 (T) behaviour for T> 10 K and a saturation for lower temperatures were found. The Meissner magnetic susceptibilitys and Hc1s angular dependences in the (bc)-plane were studied. The expression derived in the ellipsoid approximation shows a good agreement with these dependencis.

Shielding currents and current-voltage characteristics of Bi2Sr2Ca1Cu2O8+δ single crystal

Abstract The dependence of the irreversible magnetization on the external magnetic field sweep rate, d H e /d t , and its time relaxation are studied in a Bi 2+ x Sr 2+ y Ca 1+ z Cu 2 O 8+δ ( x =0.11, y =0.12, z =-0.25) single crystal. Two characteristic regions are found with a transition temperature T ∗ between 15 and 20 K depending on d H e /d t and relaxation time. Below T ∗ the magnetic field dependence of the shielding currents follows a scaling law J s ( H e , T )/ J s (0, T )= f [ H e / J s (0,T)] with a universal function f independent of temperature and sweep rate of magnetic field. Voltage-current characteristics are described quite well by a power-like law E / E c =( J s / J c ) n with n ∼1/ T . Above T ∗ a deviation from the J s ( H e ) scaling behavior and a transition to much steeper voltage-current characteristics are observed. Possible reasons of these different shielding current behaviours are discussed.

Magnetic properties of La2Cu1−xZnxO4+δ

Abstract A study of the magnetic properties of La 2 Cu 1 − x Zn x O 4 + δ (0 ≤ x ≤ 0.13; δ = 0.02) by means of magnetization measurements ( M vs T , H ) is reported. The Neel temperature of the 3D antiferromagnetic order (AF) is found to decrease with Zn substitution much more rapidly than in samples without excess oxygen. The effect of Zn substitution on the metamagnetic M vs. H transition is discussed, analyzing the temperature dependence of both the critical field H c and the weak ferromagnetic moment M s for different compositions x .

The influence of relativistic 12C ions irradiation of different critical current components in TmBa2Cu3Ox single crystals

Abstract The additional pinning, provided by 12 C ion tracks, has been found to be nearly the same for different critical current components in TmBa 2 Cu 3 O x single crystals.

Investigation on different contributions to the magnetic irreversibility in Bi2Sr2CaCu2O8 single crystals

Hysteresis cycles and relaxation measurements as a function of temperature and field are reported for a very thin Bi2Sr2CaCu2O8 single crystal (thickness=5 μm). A fishtail effect was observed between 15 and 26 K at a field of ≈400 Oe, at which the relaxation rate was found to rapidly increase. The observed behaviour gives evidence of a field-induced 3d-2d dimensional crossover in the vortex lattice in presence of different sources of irreversibility (point and extended planar defects, surface barriers), each of them dominating in different regions of the B-T phase diagram.

Flux creep, shielding current and irreversibility field in Kr irradiated Bi2Sr2CaCu2Ox single crystals

Abstract The influence of high energy Kr irradiation on the shielding current, irreversibility field and flux creep rate in Bi 2 Sr 2 CaCu 2 O x single crystals has been studied. For B « B Ψ = φ 0 ·Ψ the pinning and creep behavior is approximately independent of fluence but significantly different from the virgin state. For high magnetic fields three temperature regions were distinguished. Small changes of the irreversibility field spite of a large increase of the shielding current with fluence point that plastic deformations dominate in the low temperature regime. The high T region is determined by the single vortex-single track interaction, whereas at intermediate temperatures the pinning of several vortices by one track becomes important.

Current voltage characteristics of Bi2Sr2Ca1Cu2O8 single crystals - possible plastic deformations of the vortex lattice

Abstract The J-E curves (JEC) for Bi2+xSr2+yCa1+zCu2O8+t single crystals have been extracted from the results of VSM magnetic measurements. The obtained data show the existence of two temperature regions with a transition temperature T∗ between 15 and 20 K being dependent on the voltage criteria. Below T∗, JECs are described quite well by a power-like law E/E c = ( J/ J c ) n with n∝1/T. For high magnetic fields it is found that 1/n ∝B. A model considering the “pancake” vortex-antivortex pair excitation provides good consistency with the experimental data.

The critical current and magnetization anisotropy in TmBa2Cu3Ox and Bi2Sr2CaCu2Oy single crystals

Abstract The relations between critical current and magnetisation were derived for anisotropic superconductors The critical current and magnetisation anisotropy for TmBa2Cu3Ox and Bi2Sr2CaCu2Oy single crystals was studied.