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Measurements of the dependences of the magnetization relaxation and the magnetization hysteresis on the Au mole fraction in Y 1 Ba 2 Cu 3± ±3x Au 3x O 7± ±d superconductors have been performed to investigate the flux pinning effects. As the Au mole fraction increases, the density of the Y 1 Ba 2 Cu 3± ±3x Au 3x O 7± ±d superconductor becomes larger due to its decreased porosity. The zero-field-cooled and the fieldcooled measurements show that the critical temperatures are independent of the Au mole fraction but that the Meissner effects increase slightly with increasing Au mole fraction. The values obtained for the flux pinning potential and for the width of the magnetization decrease with increasing Au mole fraction except the Au mole fraction of 0.01. These results indicate that the flux pinning effects are decreased by substituting Au into Y 1 Ba 2 Cu 3± ±3x Au 3x O 7± ±d superconductors.

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