Enhancement of the Critical Current Densities and Trapped Flux of Gd-Ba-Cu-O Bulk HTS Doped With Magnetic Particles

For bulk HTS rotating machines, enhancement of the trapped flux is a crucial task to achieve practical applications with high torque density. The increase of critical current density J_c using artificial pinning centers is an efficient technique for the enhancement of the flux trapping properties. We attempted to enhance both J_c and the trapped flux in bulk HTS with magnetic/ferromagnetic particles additions. Fe-B-Si-Nb-Cr-Cu amorphous alloy, Fe₂O₃ and CoO particles were introduced into the Gd123 matrix. The melt growth of the single-domain bulks with different magnetic particles was performed in air. Enhancement of the critical current density J_c at 77 K was derived in the bulks with Fe₂O₃ and Fe-B-Si-Nb-Cr-Cu additions, while the superconducting transition temperature of 93 K was not degraded significantly. The experiment of the magnetic flux trapping was then conducted under static magnetic field magnetization with liquid nitrogen cooling. In the bulk with 0.4 mol% of Fe-B-Si-Nb-Cr-Cu, the integrated trapped flux exceeds over 35% compared to the one without magnetic particle addition. On the other hand, the addition of CoO particles resulted in a reduction of both J_c and trapped magnetic flux. Present results indicate that the introduction of magnetic particles gives a significant effect to the flux pinning performance.