FLUX MEASUREMENTS ON FERROMAGNETIC MICROPROBES BY ELECTRON HOLOGRAPHY

Bulk ferromagnetic microprobes, as commonly used in magnetic force mic roscopy, have been analyzed by electron holography. Using the double e xposure technique, detailed holograms have been obtained from nickel p robes. The resulting two-dimensional interferograms can be well reprod uced by numerical calculations which are based on the assumption that the probes stray field is produced by a macrodipole of several microme ters in length. By treating the dipole charge as a variational free pa rameter to be fitted against the experimental data, it is possible to determine the stray field produced by the probes, their effective leak age flux, and the surface area of a sample which may seriously be affe cted by the probes stray field. The results are considered especially important for those applications of magnetic force microscopy where th e sample is likely to be magnetically perturbed by the stray field whi ch is produced by the imaging probe itself.