Peculiarities in galvanomagnetic properties of granular YBa2Cu3O7−δ high-temperature superconductors in very weak magnetic fields

Abstract

The character of the evolution of a system of weak links in granular high temperature supercon ductors under the action of an external magnetic field H ext has been studied by measuring the current-voltage characteristics of YBa 2 Cu 3 O 7 -δ (δ ≈ 0.05) ceramic samples. The measurements have been performed at T = 77.3 K in a range of very weak magnetic fields 0 < H ext Շ 0.5H c2J , where H c2J is the upper critical field of the Josephson weak links. The results have been used to construct the field dependences of the magnetoresistance Δρ(H ext ) of the superconducting ceramics. It has been established that the parameters of the power equation E = A( j -j cJ ) ν and the magnetoresistance Δρ are nonmonotonic functions of the external magnetic field. The presence of extrema in the curves A(H ext ), j cJ (H ext ), ν(H ext ), and Δρ(H ext ) indicates that different systems of weak links between grain boundaries, which are capable of forming extended Josephson contacts, undergo sequential transitions to a resistive state with an increase in H ext .

A study of the dynamics of penetration and trapping of magnetic flux in polycrystalline YBa2Cu3O7−x samples

“…Currently, there is no exact estimate for H c1J (see, for example, Refs. [24][25][26]. For H À > H c1J , the magnetic field penetrates as vortices into the intergranular region through the distributed Josephson junctions.…”

Effect of Direct Transport Current and Heat Treatment on Resistive Properties of Bismuth-Based Ceramic High-Temperature Superconducting Oxides of Various Compositions

“…The presence of inflection points on r(I) curves for sample A implies some changes in the mechanism of weak link break down with the increase of I (Fig. 1) [1,3,4]. At low I, r of sample A is smaller by more than three orders of magnitude than that of sample B (Fig.…”

“…Review of recent works has evidenced the importance of penetration of the self magnetic field of the transport current (I) in the ceramic high-temperature superconducting (HTS) materials [1][2][3][4][5]. The interest in such investigations is caused by the need for high critical currents determined by the structural quality of the HTS samples [1][2][3][4][5][6], which is dependent on the impurity content, geometrical dimensions of the samples as well as on the thermal treatment conditions [7][8][9][10][11][12][13]. When at least two superconducting phases are presented in bismuth samples, the analysis of temperature dependence of resistivity r (T) is much more complicated [5][6][7][8][9][10].…”

“…What is more, the interpretation of these results becomes more difficult, because the ratio of superconducting and normal phases varies nonmonotonically depending on temperature, heat treatment period and impurity composition [5][6][7][8][9][10]. Besides, the peculiarities of Josephson links in weak and very weak magnetic fields [3][4] and, consequently, for small transport currents through these links are poorly known [2,3,14 ,15]. On the other hand, the importance of investigating the resistive properties of high-temperature superconductors depending on transport current is also stipulated by potential opportunity to use the obtained results in the development of high sensitivity detectors of magnetic fields.…”