Magnetic levitation force of semi-infinite type-II superconductors

Abstract

The levitation force acting on a point magnetic dipole above a semi-infinite type-II superconductor in both the Meissner and mixed states is studied. A formalism is developed for axisymmetric problems using London theory. The magnetostatic interaction energy and corresponding force can be put into closed form for such problems for arbitrary height of the magnetic point source. The results for stray fields have ready application to magnetic-force microscopy (MFM) with point probes. The results are useful for a range of experiments including the low-temperature MFM imaging of vortices and decoration measurements. Special cases include earlier results and previous approximations are obviated.