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A simple measurement technique for critical current density by using a permanent magnet

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8 Author(s)
S. Ohshima ; Fac. of Eng., Yamagata Univ., Yonezawa, Japan ; K. Takeishi ; A. Saito ; M. Mukaida
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We developed a novel nondestructive and contactless method for measurements of critical current density (Jc) in high-temperature superconductor (HTS) thin films by using a permanent magnet (Sm2Co17). This measurement technique is based on a repulsive force (Fr) and attractive force (Fa) between the magnet and HTS film caused by the shielding currents and pinning forces. The Fr and Fa were measured by using a high-resolution load sensor changing the distance (L) between the magnet and HTS film. An effective maximum repulsive force (Fm,eff) could be determined from an extrapolated value of the Fr vs. L curve for L=0 mm. We investigated the relationship of the Jc to the Fm,eff in many HTS (YBa2Cu3O7-δ and ErBa2Cu3O7-δ) samples. The standard Jc of HTS films was measured by using an inductive measurement system produced from THEVA GmbH. We found that the Jc is almost proportional to the two-thirds power of the Fm,eff normalized by the film thickness. This result indicates that the simple permanent magnet technique can be easily estimate the Jc of the HTS films. This system has good reproducibility for the Jc measurements and is useful to provide a rapid, routine characterization of the superconductivity in the HTS materials.

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IEEE Transactions on Applied Superconductivity  (Volume:15 ,  Issue: 2 )