The characterization of levitation force and attractive force of single-domain YBCO bulk under different field cooling process

The interaction forces were measured at 77 K by changing the field cooling distance Z_fc between a YBCO bulk and a permanent magnet. It is found that the maximum levitation force (F_mlf), maximum attractive force (F_maf) and the gap distance (Z_maf) corresponding to F _maf can be well described by exponential laws as a function of Z _fc, which allow us to predict these values according to Z _fc. It is also found that the distance between the Z_0fa (gap distance corresponding to the zero force) and Z_maf in the ascending process is a constant value, which can be well interpreted by the constant reduction rate of the axial component magnetic flux density along the axis line of the magnet within the constant distance. These results are very interesting to physical research and helpful for the practical designing and applications.