YBa_2Cu_3O_y中氧缺位的磁通钉扎效应

FLUX PINNING EFFECT OF OXYGEN DEFICIENCIES IN YBa_2Cu_3Oy

制备了一组不同氧含量(T_(cmid)>90K)的YBa_2Cu_3O_y单相多晶样品。对其结构、超导电性和磁通钉扎行为的观测结果表明:氧缺位导致临界电流密度J_c和钉扎力密度F_p同时增加,存在一最佳的氧缺位浓度,可使J_c和F_p有最大程度提高。与氧含量y=6.96和6.83时的情况不同,对y=6.94和6.86的样品,其J_c随磁场H非单调变化,M-H曲线上呈现“鱼尾效应”。用标度律作拟合发现,当6.83≤y≤6.94时,f_p(h)曲线的峰值都出现在同一个约化磁场h(≈0.6)处,它表明氧缺位的存在在YBa_2Cu_3O_y中引入了一种新的钉扎中心。

A series of single phase YBa2Cu3Oy samples with various oxygen contents and Tc mid's> 90K were prepared, and their structures, superconductivities, flux pinning behaviors have been determined and investigated. The experimental results show that the oxygen deficiencies result in enhancements of critical current density Jc and flux pinning force density Fp, moreover, there exists an optimal concentration of okygen deficiencies, corresponding to the maximal enhancemenes of Jc and Fp. Different from the cases of y= 6. 96,6. 83,Jc of y= 6.94,6.86 samples vary unmonotonicly with magnetic field H, correpondingly, the magnetization curves exhibit an abnormal peak known as 'fishtail' effect. Fitted with the scaling law, it is found that when 6.83≤y≤6.94, the peak in fp(h) curves appears at the same reduced magnetic field h(≈0. 6). It indicates that the existence of oxygen deficiencies introduces new flux pinning centres in YBa2Cu3Oy.c