Recently, the phenomenology of magnetic particles in aqueous media subject to external excitations has drawn strong attention. The way in which these systems move and self-organize, particularly under time-dependent excitations, has been studied in several works, and the results are of great interest both from the point of view of basic physics and of technological applications, ranging  from biomedicine, directed drug transportation  to microfluid stirring (see, for example, G. Jorge et al. J. Mag. Mag. Mater. 444 (2017) 467–471 and references therein).

In this work, we use three Helmholtz coils to generate variable magnetic fields in time and space. In particular, circularly polarized fields are applied to move micrometer nickel particles located at the bottom of a container filled with an aqueous medium. We study the time dependent displacement of these particles through the analysis of video-microscopy images. The chain structure formations are observed, as well as individual particles or groups of particles whose displacements  can be handled at will, in any spatial direction on the bottom plane  of the vessel. Here we also show that when glass microspheres are added close to the nickel particles, the microspheres motion is induced by the displacement and rotation of the magnetic particles and their hydrodynamic interactions, and this motion may be targeted after certain magnetic particle configurations are self organized.