A quantitative study of magnetic interactions between a micro-magnet array and individual magnetic micro-particles by scanning particle force microscopy

Magnetic particle force microscopy has been used to measure magnetic interactions between an array of thermomagnetically patterned hard micro-magnets and both hard magnetic and superparamagnetic microspheres. Maximum interaction forces are experienced when the microspheres scan over the interface between reversed and non-reversed zones, where the stray magnetic field produced by the micro-magnet array is maximum. Comparison of experimental and simulated force maps of the hard spheres is used to validate assumptions concerning the remanent magnetisation and depth of the reversed zones. This information is in turn used to deduce the content of magnetic nanoparticles in the superparamagnetic spheres. Asymmetries in the experimental force maps of hard spheres are attributed to (i) the existence of a weak in-plane component of the force and (ii) the fact that the transition between two regions with opposite magnetization direction is not abrupt.