Effective activation energy and phase diagram in the Er-doping MTG-YBa 2Cu 3O 7− δ crystal

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The resistivity of melted textured growth (MTG) Y 0.8Er 0.2Ba 2Cu 3O 7− δ (YErBCO) crystal has been measured as a function of temperature T, applied magnetic field H and the angle θ between the applied magnetic field and ab-plane. Based on the Yeshurun–Malozemoff model [Phys. Rev. Lett. 60 (1988) 2202], we investigated the vortex dynamic behavior from the Arrhenius form ρ( T, H)= ρ 0exp(− U 0/ T) and found that the model can explain the dissipation in the vortex liquid state for the Er-doped YBa 2Cu 3O 7− δ (YBCO) crystal. The effective activation energies for H∥ c in the Er-doped MTG-YBCO are about 2.7×10 3 K (7.5 T) and 5.6×10 4 K (0.5 T) less than that for H∥ c in pure YBCO. The anisotropy factor γ=10 obtained from the angular dependencies of effective activation energy U( θ) and the zero resistance temperature T c0( θ) for Er-doped YBCO crystal are larger those that for YBCO crystal. The field dependence of the effective activation energy U e follows a power law, U e∝ H − α , with α=1.0 for H∥ c and for various angles θ at a fixed magnetic field of 4 T. The phase diagram of the Er-doped YBCO crystal is presented and discussed.