Relationship between the magnetic field distribution and attractive force of single-domain YBCO bulk under different field cooling processes

The levitation forces under different field cooling states were measured at 77K by changing the field cooling distance Z_fc between a YBCO bulk and a permanent magnet. It is found that the relationship between the absolute maximum attractive force (F_maf) and the corresponding gap distance (Z_maf) 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 is closely related to the constant reduction factor of the axial component of flux density along the axial line of the magnet if Z_maf -Z_0fa is a constant value. These results are very interesting for fundamental research and helpful in practical designing and applications.