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 Zmaf 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.