engleski

Irreversibility line of Bi2223/Ag tape in high magnetic fields

The magnetoresistance of a (Bi,Pb)$_{2}$Sr$_{2}$ CaCu$_{2}$O$_{8+y}$ Ag sheathed tape was measured in the temperature range 15 K$\leq T\leq $120 K and magnetic field $B\leq 15$ T applied perpendicular to the broader surface of tape. Throughout the explored field range, the onset of resistivity shows Arrhenius behavior $\rho \propto \exp (-U^{\ast }(1-T/T_{cs})/k_{B}TB^{0.5})$ where $U^{\ast }$ is the sample dependent constant, and $T_{cs}$ is the temperature somewhat higher than the temperature of the resistivity onset. The observed resistance variation can be attributed to a thermally activated flux flow in a highly viscous vortex-liquid regime characterized by a plastic deformation of vortices. Experimentally determined resistive irreversibility line $B_{irr}$ vs. $T_{irr}$ follows the power-law dependence $B_{irr}(T_{irr})\propto (T_{cs}/T_{irr}-1)^{2}$ which can be derived from the exponential behavior of resistivity. Our $B_{irr}(T_{irr})$ data can also be fitted to the combination of the Josephson coupling model and depinning of pancake vortices. This fit provides very reasonable values for $B_{c2}$, $B_{c1}$, $B_{c}$, $\xi _{ab}$, $\lambda _{ab}$ and anisotropy constant $\gamma $ of Bi2212 compound, and removes the unphysical divergence of $B_{irr}(T\rightarrow 0)$ resulting from the above power-law fit.

(Bi;Pb)2Sr2Ca2Cu3O10+y Ag sheathed tape; magnetoresistance; viscous vortex-liquid regime; resistive irreversibility line

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