Calculating a parameter space to smoothly transport magnetically-trapped suspended superparamagnetic microbeads with electric-field domain wall control*

We demonstrate the capture and electrically-driven piecewise transport of superparamagnetic microbeads trapped in a magnetostatic potential energy well produced by the magnetic domain walls of Ni microrings on a [Pb(Mg$_{1/3}$Nb$_{2/3})$O$_{3}$]$_{0.66}$-[PbTiO$_{3}$]$_{0.34}$ (PMN-PT) substrate. Here I present micromagnetic simulations that illustrate the formation of field-initialized domain walls in Ni microrings and calculate the approximate force of attraction experienced by superparamagnetic microbeads near the domain walls. This force is estimated as a function of the ring geometry, bead diameter, and distance from the domain wall, and provides an upper bound for the strain-mediated, electrically-induced domain wall velocity that can be implemented to smoothly transport coupled microbeads within a fluidic environment. These results provide an initial estimate for important technological parameters and set a foundation for the optimization of this microfluidic magnetic control scheme. H. Sohn, M. Nowakowski, et al. submitted, 2014.