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

The effects of different field cooling processes on the levitation force and attractive force of single-domain YBa2Cu3O7-x (YBCO) bulk have been investigated. The forces were measured at 77 K by changing the field cooling distance Zfc between the YBCO bulk and a permanent magnet. We found that the stiffness between the YBCO and magnet increases with the decrease of Zfc; the maximum levitation force (Fmlf) of the sample decreases from 74 N to 48 N with a decrease of the Zfc from 7 cm to 0.7 cm; but the maximum attractive force (Fmaf) increases from 2.96 N to 30.6 N with a decrease of Zfc from 7 cm to 0.1 mm. Both of them obey the first decreasing exponential law. It is also found that the distance Zmaf, corresponding to Fmaf, decreases in an exponential law with the decrease of Zfc. The Fmlf, Fmaf and Zmaf are all saturated in the range of Zfc from 3 to 4 cm. All the relations between Fmlf, Fmaf and Zfc are closely related with the axial magnetic field distribution of the magnet, which allow us to easily predict the values between the Fmlf, Fmaf and Zfc, which is very helpful for practical designing and for applications. (author)