SQUID法和Campbell法测量超导材料的研究

本文对比研究了超导材料磁测量中的SQUID法和Campbell法; 并用高压PIT法制备的超导材料MgB₂作为测量样品,用两种方法,测量了超导样品的临界电流密度, 分别得到了样品的J_c-B关系曲线; SQUID法测量样品的外磁场可以达到6 T, 此时材料已经处于失超状态,此方法测得的结果是样品各个小区域结果的平均值, SQUID还可以用来进一步标度材料的钉扎力行为,研究材料磁特性. Campbell法测量只能测量到外磁场强度为0.4 T,外磁场的交流部分的频率可以达到800 Hz, 用这种测量方法得到的是整块样品的电流,由于测量计及材料内部微观结构缺陷等影响电流传输因素, 所测结果小于直流磁化法,但更切近材料实际电流,能用来深入研究材料内部结构差别对材料电性能的影响.

Study on SQUID method and Campbell method measure superconductors

The two magnetic measurement methods of superconductors, SQUID method and Campbell method, are introduced briefly. Superconducting properties of MgB₂ bulk samples are prepared by the high-pressure powder in tube (PIT) sintering method. The two measurement methods are employed to measure the critical current density of the sample. The J_c-B curves of the MgB₂ samples are obtained with each method. The SQUID method can be used to measure the magnetic strength field up to 6 T and the material is in normal state, and the result is used to scale F(b) of the pinning through necessary calculation which is used to study the magnetic characteristic of the material. The critical current density (J_c) measured by the SQUID method is the average of the materials different parts. J_c is measured and estimated by the Campbell's method. The magnetic field is only to 0.4 T while the frequency of the AC parts magnetic field is varied from 37 Hz to 797 Hz. The critical current density obtained by Campbell's method is smaller than that obtained by the SQUID measurement, which is due to the existence of various faults and the decrease of the electrical connectivity.