INTERACTION BETWEEN A MAGNETIC DIPOLE AND A SUPERCONDUCTING SPHERE

On the basis of the Meissner effect and the London theory of supercond uctivity, we theoretically studied the interaction between a magnetic point dipole and a superconducting sphere. Furthermore, the force acti ng on the tip of a magnetic force microscope from a superconducting sp here was derived on the basis of the London theory of superconductivit y. For a micro-system, we derived an analytical expression of the repe lling forces as a function of the London penetration depth lambda(T) a nd suggest an experimental method to measure lambda(T) as a function o f temperature T. From the model study, we show the invalidity of the f requency used image method for some superconductor-magnet systems. (C) 1998 Elsevier Science Ltd. All rights reserved.