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Superconductivity
Effect of temperature and magnetic field on the evolution of a vortex structure of the granular YBa$_2$Cu$_3$O$_{7-\delta}$ high-temperature superconductor
V. V. Derevyanko,
T. V. Sukhareva,
V. A. Finkel,
Yu. N. Shakhov National Science Centre Kharkov Institute of Physics and Technology
Abstract:
The temperature dependences of the electrical resistivity
$\rho(T)_{H=\operatorname{const}}$ have been measured in external magnetic fields
$\mathbf{H}_{\mathrm{ext}}$ (0
$\le H_{\mathrm{ext}}\le$ 1420 Oe) at temperatures ranging from 70 to 273 K for samples of the granular YBa
$_2$Cu
$_3$O
$_{7-\delta}$ high-temperature superconductor (HTSC). Cooling of the samples to the minimum temperature
$T_{\mathrm{min}}$ (70 K) has been performed in external magnetic fields (FC mode) and in the absence of a magnetic field (ZFC mode). Moreover, the dependences
$\rho(T)_{H=0}$ for samples cooled in the FC mode have been measured in a zero field. The curves
$\rho(T)_{H=\operatorname{const}}$ have been converted into isotherms of the magnetore-sistance
$\rho(H_{\mathrm{ext}})_{T=\operatorname{const}}$. A comparative analysis of the specific features in the behavior of the curves
$\rho(H)_{T=\operatorname{const}}$ for samples with different “magnetic prehistories” has made it possible to elucidate the nature and mechanisms of the influence of the particular scenario of the magnetic treatment of granular HTSCs on the behavior of their galvanomagnetic properties. The temperature dependences of the critical magnetic fields of superconducting grains
$(H_{c1g}$,
$H_{c2g}$) and Josephson weak links
$(H_{c2J})$ have been determined, and the
$H$–
$T$ phase diagrams of granular YBa
$_2$Cu
$_3$O
$_{7-\delta}$ HTSCs have been recovered.
Received: 15.07.2013
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