Trapped magnetic field and levitation force properties of multi-seeded YBCO superconductors with different seed distance

The performance of large grain (RE)BCO superconducting bulks has the significant potential for magnetic-force based applications such as trapped field magnets and magnetic levitation devices. These materials can trap high magnetic fields of several tesla at temperature below 77 K and also provide stable levitation and high load capacity in magnetic levitation systems. Top seeded melt growth process and multi-seeding technique have been used to enlarge bulk (RE)BCO samples, however many factors affect the growth of multi-seeded bulk (RE)BCO. These include the geometry of sample, the distance between seed crystal, the seed combination and alignment. In this work, we investigated the effects of the distance (d) between two Nd1.8Ba2.4Cu3.4O7 (Nd-123) seed crystals on the characteristics of the (100)//(100) grain junction of top-seeded melt growth (TSMG) processed YBCO bulk superconductors. Four cylindrical shaped Y-Ba-Cu-O samples of dimensions 25 mm in diameter and 7 mm in height with two seed crystals were prepared for this investigation. The fabrication process of these samples is described and their trapped magnetic field and vertical levitation force were measured at 77 K and lower temperatures under Zero-field-cooled (ZFC) and Field-cooled (FC) regimes. We found that both the trapped magnetic field and the vertical levitation force decreased with increasing d value. The trapped field and the vertical levitation force values of the samples with the decreasing the distance between two seed crystals from 16 mm to 1 mm, increased from 0,62 T to 0,78 T and from 13.08 N to 19.41 N, respectively. A peak trapped field value of 4.20 T and vertical levitation force of 19. 41 N has been achieved in this study for YBCO with the distance between two seed crystals of 1 mm. The obtained results can be contributing the properties on improvement of the levitation force and trapped magnetic field and these properties induce widespread usage of multi-seeded YBCO bulks in technological applications. (C) 2020 Elsevier B.V. All rights reserved.