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We present a microwave study of the angular dependence of the flux-flow resistivity $rho_{ff}$ and of the pinning constant $k_p$ in YBCO thin films containing BZO nanorods. We find that BZO nanorods are very efficient pinning centers, even in tilted fields. We find that $rho_{ff}$ is a scaling function of a reduced field $H/f(theta)$. We extend a model for the anisotropic motion of vortices in uniaxially anisotropic superconductor, able to describe the experimental $f(theta)$ on the basis of only the intrinsic anisotropy of YBCO. The pinning constant $k_p$, by contrast, exhibits different field dependences in different angular ranges, consistent with pinning by BZO at angles as large as 60$^{circ}$, and with pinning along the $a,b$ planes as originating from the same mechanism as in pure YBCO with the field along the c axis.
56 - N. Pompeo , R. Rogai , M. Ausloos 2011
We report on microwave measurements on DyBa$_2$Cu$_3$O$_{7-rmdelta}$ monodomains grown by the top-seeded melt-textured technique. We measured the field increase of the surface resistance $R_{rm s}(H)$ in the a-b plane at 48.3 GHz. Measurements were p erformed at fixed temperatures in the range 70 K - $T_{rm c}$ with a static magnetic field $mu_0H<0.8$ T parallel to the c-axis. Low field steep increase of the dissipation, typical signature of the presence of weak links, is absent, thus indicating the single-domain behaviour of the sample under study. The magnetic field dependence of $R_{rm s}(H)$ is ascribed to the dissipation caused by vortex motion. The analysis of $X_{rm s}(H)$ points to a free-flow regime, thus allowing to obtain the vortex viscosity as a function of temperature. We compare the results with those obtained on RE-BCO systems. In particular, we consider strongly pinned films of YBa$_2$Cu$_3$O$_{7-rmdelta}$ with nanometric BaZrO$_3$ inclusions.
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