Vortex dynamics study on an uniaxially textured YBCO/MgO superconducting film from magnetic measurements

The vortex dynamics of an undoped uniaxially textured YBa2Cu3O7-δ (YBCO) superconducting film grown onto a MgO (100) substrate was inspected by applying the vortex glass and collective-pinning models. The texture and structural characterization studied by XRD revealed a uniaxially (00l) YBCO layer, which coexists with minor Y2BaCuO5 and CuO phases. The temperature dependence of the magnetization in the superconducting state reveals a critical temperature TC = 88 K. By measuring the hysteresis loops (M(H)) at 10 - 70 K, the critical fields HC1, HC2, HP and Hirr were estimated and a vortex matter diagram is sketched. By using the Bean model, the critical current density values JC(T,H) are obtained and the typical peak effect is observed. The vortex dynamics mechanism is discussed taking into account four vortex feature regimes in the double-logarithmical JC(H) curves. The vortex pinning mechanism is discussed by obtaining the pining force, FP, its normalization, f(h), and magnetic relaxation M(t) measurements taken in field cooling (FC) mode at 10 – 60 K. The glassy exponent μ and the characteristic energy U(J, T) in the vortex glass model were estimated following the Maley method. The collective-pinning model is used to discuss the possible vortex regimes mechanism (individual flux lines, small bundles and large bundles of pinned flux). Eventually, the E(J) curves, expressed from the swept field and creep measurements, show a power-law behaviour, in agreement with the vortex matter.