高J_c熔融织构YBa_2Cu_3O_y块材的磁性质与钉扎机制

MAGNETIC PROPERTIES AND PINNING MECHANISMOF HIGH Jc MELT-TEXTURED YBa_2C_3OyBULK SAMPLE

在不同温度和磁场下测量了熔融织构YBa_2Cu_3O_y块材的磁衰减和磁滞回线.在20K<T<70K的温区和2T<B<ST的磁场范围内发现样品的磁化强度绝对值随磁场的增强而增大.还发现衰减曲线M(t)与对数律有明显偏离,而相对衰减率s(=dln|M|dlns)的绝对值随温度的升高和磁场的增强而减小.为解释这些现象而对样品的钉扎机制进行了分析.由两种方法在很大的电流密度范围内得到了样品磁通有效热激活能与电流密度的关系U(J)=U_(o)(J_(cs)/J)^(?)-1]/μ 在此基础上,利用合作钉扎理论解释了实验结果,并通过对实验结果的直接拟合得出μ,J_(ca),U.等物理量与磁场的关系.这些关系符合合作钉扎理论的预期.还讨论了织构样品与单晶之间的差异.

The magnetic relaxation and hysteresis loops of melt-textured YBa2Cu3Oy bulk sample were measured at different temperatures and in different fields. The absolute value of magnetization M was found to increases with the applied field B when 2T<B<8T in the temperature range 20K<T<70K. Also found was that the relaxation curve deviates from logarithmic law apparently, the relative relaxation rate decreases rapidly as temperature increases or field increases. The pinning mechanism was investigated in order to explain these properties. The function between the effective activation energy U and current density J over a wide range of J was gained through two meathods, which is of the form U(J)=(U0/μ)[(Jc0/J)μ-1]. Based on this, the collective pinning theory was used to explain the experimental results. The field dependence of μ, Jc0 and U0 was obtained through direct fit of the measured U(J) curves, which is in good agreement with collective pinning theory. Also discussed was the difference between our sample and YBa2Cu3O7 single crystal.