Jc. Wei et al., MAGNETIC FORCE ACTING ON A MAGNETIC DIPOLE OVER A SUPERCONDUCTING THIN-FILM, Physical review. B, Condensed matter, 54(21), 1996, pp. 15429-15437
The magnetostatic interaction energy and corresponding magnetic force
acting on a magnetic point dipole placed above a type-II thin supercon
ducting film in the mixed state with a single vortex are calculated us
ing electromagnetics coupled with the London theory of superconductivi
ty. If a vortex is trapped by a circular defect of radius b much less
than Lambda, the magnetic forces, caused by the vortex, differ from th
e results of free from defect pinning by the factor (1 - b/Lambda), wh
ere Lambda is the effective penetration depth. The possibility of form
ation of the vortex in the thin film only in the field of the magnetic
point dipole is investigated. The critical position of the dipole for
creating the first vortex under the electromagnetic pinning of a circ
ular defect and that position in the absence of defect pinning are obt
ained for comparison. In particular, in the limit of a/Lambda much gre
ater than 1, where a is the separation between the dipole and the thin
film, the only difference between two results is in the cutoff length
, i.e., in the case of a circular defect the only difference in the cr
itical position calculation is the cutoff at radius b rather than at c
oherence length xi. The pinning force of a single vortex by a circular
defect is also calculated. Further, we investigate the conditions of
the vortex creation for various cases (including the first, second, an
d third vortices) for a free of pinning center in the examining region
. It is found that the creation of a new single vortex in the thin fil
m causes an abrupt change in vertical levitation force: the force chan
ged discontinuously.