Magnetovoltage Measurements and Hysteresis Effects in Polycrystalline Superconducting Y1Ba2Cu3O7−x/Ag in Weak Magnetic Fields

• Published in: Journal of superconductivity and novel magnetism 2013-10, Vol.26 (10), p.3085-3098
• Main Authors: Altinkok, A., Kiliç, K., Olutaş, M., Kiliç, A.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cuprates superconductors (high tc and insulating parent compounds); Exact sciences and technology; Magnetic Materials; Magnetism; Original Paper; Physics; Physics and Astronomy; Properties of type I and type II superconductors; Proximity effects, weak links, tunneling phenomena, and josephson effects, adreev effect, sn and sns junctions; Strongly Correlated Systems; Superconductivity; Vortex lattices ,flux pinning, flux creep; Y-based cuprates
• ISSN: 1557-1939; 1557-1947
• DOI: 10.1007/s10948-013-2139-y

The magnetovoltage measurements ( V – H curves) with different sweeping rates ( dH / dt ) of the external magnetic field in Ag-added polycrystalline YBa 2 Cu 3 O 7− x sample (YBCO/Ag) were investigated. The measurements of V – H curves were carried out as functions of the transport current ( I ) and temperature ( T ). Upon cycling  H , all V – H curves measured for different values of I exhibit a clockwise hysteresis effects in forward region. The hysteresis effects in the V – H curve were interpreted in terms of two-level magnetic system, which considers the superposition of the external magnetic field and the local magnetic fields in the intergrain boundaries induced by magnetic dipole moment of neighbor superconducting grains. The analysis of magnetovoltage data showed that the flux trapping in the junction network has a negligible effect on the evolution of the V – H curves and the irreversibilities arise mainly from the flux trapping inside the grains. It is shown that the width of V – H curves shows a universal scaling behavior with respect to the applied current below the critical temperature  T c . The comparison of V – H curves of the YBCO/Ag sample with those of YBCO shows that adding Ag to the superconducting structure weakens the pinning properties of Josephson medium and provokes the instabilities in measured dissipation. The presence of Ag in the superconducting matrix causes marked decrease in hysteresis effects and makes the V – H curves d H /d t dependent. At high values of dH / dt , the instabilities and plateau regions in V – H curves increase significantly as compared to those of observed in YBCO. In addition, the interrelation between the evolution of V – H curves obtained for different values of I and the critical current I c was demonstrated experimentally.