The effect of different field cooling processes on the levitation force and attractive force of single-domain YBa₂Cu₃O7 xbulk

The effects of different field cooling processes on the levitation force and attractive force of single-domain YBa 2 Cu 3 O 7− x (YBCO) bulk have been investigated. The forces were measured at 77 K by changing the field cooling distance Z fc between the YBCO bulk and a permanent magnet. We found that the stiffness between the YBCO and magnet increases with the decrease of Z fc ; the maximum levitation force ( F mlf ) of the sample decreases from 74 N to 48 N with a decrease of the Z fc from 7 cm to 0.7 cm; but the maximum attractive force ( F maf ) increases from 2.96 N to 30.6 N with a decrease of Z fc from 7 cm to 0.1 mm. Both of them obey the first decreasing exponential law. It is also found that the distance Z maf , corresponding to F maf , decreases in an exponential law with the decrease of Z fc . The F mlf , F maf and Z maf are all saturated in the range of Z fc from 3 to 4 cm. All the relations between F mlf , F maf and Z fc are closely related with the axial magnetic field distribution of the magnet, which allow us to easily predict the values between the F mlf , F maf and Z fc , which is very helpful for practical designing and for applications.