2D transport of superparamagnetic microbeads on a ferromagnetic hexagonal nanolattice

Summary form only given. Surface-functionalized superparamagnetic (SPM) beads have been widely used to detect and manipulate chemical and biological agents in lab-on-a-chip systems. Recently, it has been shown that by exploiting the stray field generated by domain walls in magnetic nanostructures, it is possible to capture and couple a SPM bead to a domain wall. To store the captured bead, the domain walls can be pinned by fabricating geometrical defects on the nanotracks. Furthermore, the position of the coupled SPM bead can be pinpointed by measuring the magnetoresistance across nanotrack sections. However, studies on such systems have so far been limited to 1D transport. In this work, we develop a novel structure to manipulate SPM beads across a substrate surface. While domain wall trajectory under a constant field has been studied, we found that by applying a bias field in the direction of a branch, the domain wall can be forced to propagate in the direction of the selected branch. Replicating the structure into a lattice of 120° V-branches similar to a honeycomb pattern, we can finally shuttle the SPM beads across a 2D surface. By changing the width and thickness of the nanowire, the pinning potential energies of different domain boundaries were investigated. To verify the simulation results, a unit cell of the hexagonal lattice was fabricated using a combination of electron beam lithography and magnetron sputtering. A V-branch fabricated to study the amount of bias field needed to force the domain wall to propagate in the intended direction is shown. Our results show that it is indeed possible to shuttle SPM beads across a 2D surface with the application of a pulsed magnetic field with varying in-plane directions.