Suspension effect of BiPbSrCaCuO ceramics

Magnetic flux measurements of a toroidal magnet revealed a concave shaped field distribution with a single minimum value and a null field along the axis of the torus at the point where the field was reversed. The non-linear magnetic field of the toroidal magnet perpendicular to the Ag2O-doped superconducting disk sample with the trapped magnetic flux distorted the field line distribution. As a result, the interaction force between the magnet and sample exhibited regions of repulsive, null, attractive, null, and finally repulsive force. The asymmetrical concave shaped force pattern along the axis with two null force points indicates that the magnetic force exerted form the sample changed direction which resulted in the transition from repulsive force to attractive force at the null force point, and the force becomes repulsive again beyond the second null force point as the distance along the axis increases. The lateral stability of the suspended sample under the toroidal magnet is provided by the characteristics of the symmetrical nature of the field line with respect to the axis of the magnet. The magnetic moment of an undoped and 2% Ag2O-doped sample was shown to be m=0.043 and 0.06 emu, respectively. The measured suspension force exerted form the doped sample agreed well with the suspension force calculated from magnetostatic force distribution.