Transport of magnetic microparticles via tunable stationary magnetic traps in patterned wires

Remote manipulation of fluid-borne magnetic particles on a surface is useful to probe, assemble, and sort microscale and nanoscale objects. In this paper, fields emanating from magnetic domain walls in zigzag wires as well as from magnetization distributions in notched Co0.5Fe0.5 wires patterned on a silicon surface are shown to act as effective traps for such objects. Weak (similar to 100 Oe) in- and out-of-plane external magnetic fields modify the energy landscape, allowing for the entrapped objects to be remotely maneuvered along predetermined routes across the surface while the magnetization profiles at the wire vertices and notches remain stationary. In calculating the forces, the net magnetic field and its spatial distribution are determined by modeling the wire magnetization using micromagnetic simulation or by approximating the trap as a point source of fields. The applicability of these models to particle manipulation under the experimental conditions is discussed.