The levitation force of bulk RE-Ba-Cu-O (RE: rare earth elements) superconductors can be drastically increased by increasing the strength of the external field. We have studied the effects of the temperature and magnetic field on the levitation force and its time relaxation in the field range of 0-2 T by using a superconducting magnet as a magnetic field source. The samples we used were bulk Y-Ba-Cu-O and Sm-Ba-Cu-O superconductors 46 mm in diameter and 15 mm in thickness, which were fabricated with a top-seeded melt-growth process. The levitation forces were measured by applying the magnetic fields of 0-2 T at 10-80 K. It was found that the levitation force increased with decreasing temperature in both Y-Ba-Cu-O and Sm-Ba-Cu-O. The time relaxation of the levitation force was also reduced with lowering temperature. Sm-Ba-Cu-O exhibited better performance in the levitation force and its time relaxation only in a high temperature and high field region.
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